Electronic Materials and Devices Laboratory

WELCOME to the Electronic Materials & Devices Lab

The Electronic Materials and Devices Lab (EMDL) formed in 1991 by Professor Steve Ringel when he arrived in the Department of Electrical and Computer Engineering at Ohio State as an assistant professor. Since then, EMDL has grown to support the graduation of 25 PhD students, 52 MS students, 11 postdoctoral researchers and many undergraduate research students carrying out research supported by U.S. government agencies, industry and the state of Ohio. EMDL graduates have gone on to become vice presidents of major technology companies, distinguished research scientists at government labs, distinguished faculty at leading universities in the U.S. and overseas, senior engineers, technology entrepreneurs, and even a patent attorney! EMDL students, staff and faculty are engaged in research collaborations across Ohio, the U.S. and many countries in Europe, Asia and Australia.

EMDL research sits at the nexus of device engineering, electronic materials, applied physics and chemistry, with focus areas on photovoltaics, electronic devices, power electronics, and optoelectronics. We routinely partner with industry collaborators through a variety of corporate engagements, some of which are intertwined with the OSU Institute for Materials Research (imr.osu.edu) for which Professor Ringel is the current and founding director (since 2006). EMDL students come from a range of academic backgrounds that include electrical engineering, materials science and engineering, physics, chemistry, mechanical engineering and chemical engineering. Both interdisciplinary research and basic research that has translational impact on technology are strongly encouraged! A sampling of typical EMDL research projects focus on:

III-V compound semiconductor photovoltaics for space and terrestrial applications
III-V/Si heteroepitaxial integration, lattice-mismatched heterostructures
Defect characterization
Epitaxial growth (Molecular beam epitaxy & metalorganic chemical vapor deposition)
ultra-wide bandgap gallium oxide materials and devices
wide bandgap gallium nitride materials, RF devices and power transistors
defects and reliability in UWBG and WBG transistors and CIGS solar cells
radiation effects in semiconductor materials and devices

An idea of what EMDL is all about can be found via the various links on this simple website.

For more information about research opportunities please contact any of the EMDL faculty – Steve Ringel, Tyler Grassman or Aaron Arehart.

Thanks for visiting EMDL!

Steven A. Ringel

ringel.5@osu.edu

Distinguished University Professor

Neal A. Smith Endowed Chair of Electrical Engineering

Associate Vice President for Research, OSU Office of Research

Executive Director, Institute for Materials Research

If you have an update for this page please contact Jennifer Donovan donovan.205@osu.edu

Graduate Student	Year	Degree	Thesis/Dissertation
Daniel Lepkowski	2021	PhD	GaAs0.75P0.25/Si Tandem Solar Cells: Design Strategies and Materials Innovations Enabling Rapid Efficiency Improvements
Jacob Boyer	2020	PhD	Epitaxy and Characterization of Metamorphic Semiconductors for III-V/Si Multijunction Photovoltaics
Wenyuan Sun	2020	PhD	Impact of traps on GaN RF and power transistors performance and reliability
Pran Paul	2019	PhD	Impact of deep traps on CIGS solar cell performance and reliability
Kevin Galiano	2019	PhD	Scanning Probe Microscopy Measurements and Simulations of Traps and Schottky Barrier Heights of Gallium Nitride and Gallium Oxide
Esmat Farzana	2019	PhD	Defects and Schottky Contacts in beta-Ga2O3: Properties, Influence of Growth Method and Irradiation
Daniel Chmielewski	2018	PhD	III-V Metamorphic Materials and Devices For Multijunction Solar Cells Grown Via MBE and MOCVD
Christine Jackson	2018	PhD	Correlations of Electronic Interface States and Interface Chemistry on Dielectric/III-Nitride Heterostructures for Device Applications
Julia Deitz	2018	PhD	Bridging the Gap: Probing Structure-Property Relationships in Functional Materials through Advanced Electron Microscopy Based Characterization
Nathan Vaughn	2016	MS	(Non-Thesis MS)
Zeng Zhang	2015	PhD	Deep Level Defects in Advanced III-Nitride Semiconductors: Presence, Properties and Impact of Proton Irradiation
Anup Sasikumar	2014	PhD	Quantitative spectroscopy of reliability limiting traps in operational gallium nitride based transistors using thermal and optical methods
Christopher Ratcliff	2014	PhD	Growth and Characterization of III-Phosphide Materials and Solar Cells for III-V/Si Photovoltaic Applications
Emre Cinkilic	2013	MS	Comparison of Interface State Spectroscopy Techniques by Characterizing Dielectric – InGaAs Interfaces
Santosh Hariharan	2013	MS	(Non-Thesis MS)
Andrew M. Carlin	2012/2010	PhD/MS	Dissertation: Materials Integration and Metamorphic Substrate Engineering from Si to GaAs to InP for Advanced III-V/Si Photovoltaics Thesis: Growth and Strain Relaxation in Anion-Graded GaxIn1-xAsyP1-y
Krishna Swaminathan	2012	PhD	Multi-spectral Photodetectors on GaAs Substrates using Metamorphic Epitaxy and Hybrid III-V Heterostructures
Mark R. Brenner	2009	MS	GaP/Si Heteroepitaxy (Suppression of Nucleation Related Defects)
Andrew C. Malonis	2009	MS	Quantitative defect spectroscopy on operating AlGaN/GaN high electron mobility transistors
Aaron R. Arehart	2009	PhD	Investigation of electrically active defects in GaN, AlGaN, and AlGaN/GaN high electron mobility transistors
Maria Gonzalez	2009	PhD	Electronic Defects of III-V Compound Semiconductor Materials Grown on Metamorphic SiGe Substrates for Photovoltaic Applications
Yong Lin	2007	PhD	Science and applications of III-V graded anion metamorphic buffers on INP substrates
Katherine L. Dykes	2007	MS	Surface Treatment and Characterization of Alloy SiGe in Preparation for MBE Growth Applications
Andrew M. Armstrong	2006	PhD	Investigation of deep level defects in GaN:C, GaN:Mg and pseudomorphic AlGaN/GaN films
Ojin Kwon	2005	PhD	Monolithic integration of III-V optoelectronics on SI
John J. Boeckl	2005	PhD	Microstructural investigation of defects in epitaxial GaAs grown on mismatched Ge and SiGe/Si substrates
Matthew R. Lueck	2005	MS	Impact of Annealing and Flux Ratio on MBE Grown GaInP Materials and Solar Cells
Carrie L. Andre	2004	PhD	III-V semiconductors on SiGe substrates for multi-junction photovoltaics
Robert J. Kaplar	2002	PhD	Characterization of deep-level defects in indium-gallium-arsenic-nitride
Piyush M. Sinha	2002	MS	Electron Transport Properties of MBE Grown InAsP
John A. Carlin	2001/2000	PhD/MS	Dissertation: Investigation and development of high quality gallium arsenide-on-silicon for space photovoltaics using a graded germanium silicon buffer Thesis: Role of Al Content on Surface Roughening and Critical Thickness of Low Temperature AlxGa1-xAs
Adrian Hierro	2001	PhD	Electrical characterization of defects in n-gallium nitride
Robert M. Sieg	1998/1994	PhD/MS	Dissertation: Critical issues in III-V compound semiconductor epitaxy on group IV (silicon, germanium) substrates for optoelectronic applications Thesis: A PL Study of Heavily Doped InP
Basab Chatterjee	1997	PhD	Hydrogen passivation of heteroepitaxial indium phosphide
William C. Davis	1997	MS	Digital Deep Level Transient Spectroscopy: Improved Data Analysis and Semiconductor Device Characterization through Linear Predictive Modeling
Patrick N. Grillot	1996/1993	PhD/MS	Dissertation: Defects induced by strain-relaxation in heteroepitaxial germanium-silicon alloys Thesis: Analysis of the Electronic Properties of Dislocations in Heteroepitaxial Germanium-Silicon
Rafael A. Mena	1995	PhD	Novel measurement techniques for the characterization of advanced HEMT structures for communication applications

Post Doctoral Researchers	Years
Christine Jackson	2018-2019
Drew Cardwell	2013-2015
Santino Carnevale	2013-2015
Javier Grandal	2010-2012

Visiting Scholars	Years
Alicia Gonzalo Martin	2016
Alejandro Kurtz de Griñó	2014
Elisa Garcia-Tabarés	2013
Beatriz Galiana-Blanco	2011-2012
Emre Gur	2009-2012

Undergraduate Students	Year		Undergraduate Degree
Allison Whitney	2020		BS, Materials Science and Engineering
Luke (Shining) Xu	2018		BS, Materials Science and Engineering
Amber Silvaggio	2017		BS, Electrical and Computer Engineering
Deep Shah	2015		BS, Chemical and Biomolecular Engineering
Austin Speelman	2012		BS, Electrical and Computer Engineering

2022

E. C. Hettiaratchy, B. Wang, A. Dheenan, J. McGlone, N. K. Kalarickal, N. Bagués, S. Ringel, D. W. McComb, S. Rajan, and R. C. Myers, “Quantitative x-ray diffraction analysis of strain and interdiffusion in β-Ga2O3 superlattices of μ-Fe2O3 and β-(AlxGa1−x)2O3,” Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, vol. 40, no. 6, p. 062708, Nov. 2022. DOI: 10.1116/6.0002207
A. V. Dheenan, J. F. McGlone, N. K. Kalarickal, H.-L. Huang, M. Brenner, J. Hwang, S. A. Ringel, and S. Rajan, “β-Ga₂O₃ MESFETs with insulating Mg-doped buffer grown by plasma-assisted molecular beam epitaxy,” Appl. Phys. Lett., vol. 121, no. 11, p. 113503, Sep. 2022. DOI: 10.1063/5.0103978
Hemant Ghadi, Joe F. McGlone, Evan Cornuelle, Zixuan Feng, Yuxuan Zhang, Lingyu Meng, Hongping Zhao, Aaron R. Arehart, and Steven A. Ringel, "Deep level defects in low-pressure chemical vapor deposition grown (010) β-Ga2O3", APL Materials 10, 101110 (2022) https://doi.org/10.1063/5.0101829
Kevin Goodman, Sam McHenry, Jeff Titus, Robert Cooper, Hemant Ghadi, Steve Ringel, Kazuki Nomoto, Wenshen Li, Dobrin P. Bossev, Debdeep Jena, Huili Grace Xing, Matthew J. Gadage, and Matthew R. Halstead, “Photoelectric Generation Coefficient of B-Gallium Oxide during Exposure to High-Energy Ionizing Radiation,” Phys. Status Solidi A 2022, 279, 2100700 (2022). DOI: 10.1002/pssa.202100700
Andrew J. Green, James Speck, Grace Xing, Peter Moens, Fredrik Allerstam, Krister Gumaelius, Thomas Neyer, Andrea Arias-Purdue, Vivek Mehrotra, Akito Kuramata, Kohei Sasaki, Shinya Watanabe, Kimiyoshi Koshi, John Blevins, Oliver Bierwagen, Sriram Krishnamoorthy, Kevin Leedy, Aaron R. Arehart, Adam T. Neal, Shin Mou, Steven A. Ringel, Avinash Kumar, Ankit Sharma, rishnendu Ghosh, Uttam Singisetti, Wenshen Li, Kelson Chabak, Kyle Liddy, Ahmad Islam, Siddharth Rajan, Samuel Graham, Sukwon Choi, Zhe Cheng, and Masataka Higashiwaki, β-Gallium oxide power electronics,” APL Mater. 10, 029201 (2022); https://doi.org/10.1063/5.0060327

2021

N.K. Kalarickal, Z. Feng, A.F.M. Anhar Uddin Bhuiyan, Z. Xia, W. Moore, J.F. McGlone, A.R. Arehart, S.A. Ringel, H. Zhao and S. Rajan, “Electrostatic engineering using extreme permittivity materials for ultra-wide bandgap semiconductor transistors,” IEEE Trans. Electron Devices 68 (1), pp. 29-35 2021, https://doi.org/10.1109/TED.2020.3037271
D. J. Chmielewski, D. L. Lepkowski, J. T. Boyer, T. J. Grassman and S. A. Ringel, "Metamorphic Tunnel Junctions Grown Via MOCVD Designed for GaAs0.75P0.25/Si Tandem Solar Cells," in IEEE Journal of Photovoltaics, vol. 11, no. 2, pp. 408-414, March 2021, https://doi.org/10.1109/JPHOTOV.2021.3052773
D. L. Lepkowski, T. Kasher, T. J. Grassman and S. A. Ringel, "Designing an Epitaxially-Integrated DBR for Dislocation Mitigation in Monolithic GaAsP/Si Tandem Solar Cells," in IEEE Journal of Photovoltaics, vol. 11, no. 2, pp. 400-407, March 2021, https://doi.org/10.1109/JPHOTOV.2020.3043105
Yuxuan Zhang, Zhaoying Chen, Wenbo Li, Aaron R. Arehart, Steven A. Ringel, Hongping Zhao, “Metalorganic Chemical Vapor Deposition Gallium Nitride with Fast Growth Rate for Vertical Power Device Applications,” in Physica Status Solidi Applied Research, vol. 218, no.6, 2000469 MARCH 2021 https://doi.org/10.1002/pssa.202000469
Daniel L. Lepkowski, Tyler J. Grassman, Jacob T.B oyer, Daniel J. Chmielewski, Chuqi Yi, Mattias K. Juhl, Anastasia H. Soeriyadi, Ned Western, Hamid Mehrvarz, Udo Römer, Anita Ho-Baillie, Christopher Kerestes, Daniel Derkacs, Steven G .Whipple, Alex P. Stavrides, Stephen P.Bremner, Steven A. Ringel, “23.4% monolithic epitaxial GaAsP/Si tandem solar cells and quantification of losses from threading dislocations,” in Solar Energy Materials and Solar Cells, Vol. 230, Sept. 15, 2021, 111299 https://doi.org/10.1016/j.solmat.2021.111299

2020

Hemant Ghadi, Joe F McGlone, Zixuan Feng, AFM Anhar Uddin Bhuiyan, Hongping Zhao, Aaron R Arehart, Steven A Ringel, “Influence of growth temperature on defect states throughout the bandgap of MOCVD-grown β-Ga2O3 editors-pick” Appl. Phys. Lett. 117, 172106; https://doi.org/10.1063/5.0025970. (OCT 2020)
Yuxuan Zhang, Zhaoying Chen, Wenbo Li, Hyunsoo Lee, Md Rezaul Karim, Aaron R Arehart, Steven A Ringel, Siddharth Rajan, Hongping Zhao, “Probing unintentional Fe impurity incorporation in MOCVD homoepitaxy GaN: Toward GaN vertical power devices,” Journal of Applied Physics 127, 215707; https://doi.org/10.1063/5.0008758 (JUNE 2020)
Nidhin Kurian Kalarickal, Zhanbo Xia, Joe F McGlone, Yumo Liu, Wyatt Moore, Aaron R Arehart, Steven A Ringel, Siddharth Rajan. “High electron density β-(Al0.17Ga0.83)2O3/Ga2O3 modulation doping using an ultra-thin (1 nm) spacer layer editors-pick,” Journal of Applied Physics 127, 215706; https://doi.org/10.1063/5.0005531 (JUNE 2020)
Nidhin Kurian Kalarickal, Zixuan Feng, AFM Bhuiyan, Zhanbo Xia, Joe F McGlone, Wyatt Moore, Aaron R Arehart, Steven A Ringel, Hongping Zhao, Siddharth Rajan, “Electrostatic Engineering using Extreme Permittivity Materials for Ultra-wide Bandgap Semiconductor Transistors," arViv, https://arxiv.org/abs/2006.02349v1 (JUNE 2020)
Zixuan Feng A FM Anhar Uddin Bhuiyan Zhanbo Xia Wyatt Moore Zhaoying Chen Joe F. McGlone David R. Daughton Aaron R. Arehart Steven A. Ringel Siddharth Rajan Hongping Zhao, “Probing Charge Transport and Background Doping in Metal‐Organic Chemical Vapor Deposition‐Grown (010) β‐Ga2O3,” Rapid Research Letters, 14:8 https://doi.org/10.1002/pssr.202000145. (MAY 2020)
D. L. Lepkowski, T. Kasher, J. T. Boyer, D. J. Chmielewski, T. J. Grassman and S. A. Ringel, "The Critical Role of AlInP Window Design in III–V Rear-Emitter Solar Cells," in IEEE Journal of Photovoltaics, vol. 10, no. 3, pp. 758-764, https://doi.org/10.1109/JPHOTOV.2020.2978863. (MAY 2020)
Hemant Ghadi, Joe F McGlone, Christine M Jackson, Esmat Farzana, Zixuan Feng, AFM Anhar Uddin Bhuiyan, Hongping Zhao, Aaron R Arehart, Steven A Ringel, “Full bandgap defect state characterization of β-Ga2O3 grown by metal organic chemical vapor deposition,” APL Materials 8, 021111 (2020); https://doi.org/10.1063/1.5142313. (JAN 2020)

2019

D.L. Lepkowski, J.T. Boyer, D.J Chmielewski, A.C. Silvaggio, S.A. Ringel and T.J. Grassman, Investigation of Rear-Emitter GaAs0.75P0.25Top Cells for Application to III–V/SiTandem Photovoltaics,“ IEEE Journal of Photovoltaics 9(6), 1644-1651 (NOV 2019) https://doi.org/10.1109/JPHOTOV.2019.2939069
Z. Xia, H. Chandrasekar, W.Moore, C. Wang, A.J. Lee, J. McGlone, N.K. Kalarickal, A. Arehart, S.A. Ringel, F, Yang and S, Rajan, “Metal/BaTiO3/β-Ga2O3 dielectric heterojunction diode with 5.7 MV/cm breakdown field,”Appl. Phys. Lett. 115, 252104, (DEC 2019) https://doi.org/10.1063/1.5130669
E. Farzana, A. Mauzi, J. B. Varley, T. Blue, J. S. Speck, A. R. Arehart, and S. A. Ringel, “Influence of Neutron Irradiation on Deep Levels in Ge-doped (010) β-Ga2O3 layers grown by plasma-assisted molecular beam epitaxy,” APL Materials 7 (12), 121102 (DEC 2019) https://doi.org/10.1063/1.5126463
N. K. Kalarickal, Z. Xia, J. McGlone, S. Krishnamoorthy, W. Moore, M. Brenner, A. R. Arehart, S. A. Ringel, and S. Rajan, “Mechanism of Si doping in plasma assisted MBE growth of β‑Ga2O3,” Appl. Phys. Lett., 115 (15), 152106 (OCT 2019) https://doi.org/10.1063/1.5123149
J. M. Johnson, Z. Chen, J. B. Varley, C. M. Jackson, E. Farzana, Z. Zhang, A. R. Arehart, H. Huang, A. Genc, S. A. Ringel, C. G. Van de Walle, D. A. Muller, and J. Hwang, “Unusual Formation of Point Defect Complexes in the Ultra-wide Band Gap Semiconductor β-Ga2O3,” Phys. Rev. X, 9 (4), 041027 (NOV 2019) https://doi.org/10.1103/PhysRevX.9.041027
H. Chandrasekar, J. Cheng, T. Wang, Z. Xia, N.G. Combs, C.R Freeze, P.B Marshall, J. McGlone, A. Arehart, S.A. Ringel, A. Janotti, S. Stemmer, W. Lu and S.Rajan, "Velocity saturation in La-doped BaSnO3 thin films,” Appl. Phys. Lett., 115 (15), 092102 (AUG 2019) https://doi.org/10.1063/1.5097791
J. F. McGlone, Z. Xia, C. Joishi, S. Lodha, S. Rajan, S. Ringel, and A. R. Arehart, “Identification of critical buffer traps in Si δ-doped β-Ga2O3 MESFETs,” Appl. Phys. Lett., 115 (15), 153501, (OCT 2019 - Online) https://doi.org/10.1063/1.5118250
C. Joishi, Y. Zhang, Z. Xia, W. Sun, A.R Arehart, S.A. Ringel, S. Lodha and S. Rajan, “Breakdown Characteristics of β -(Al0.22Ga0.78)2O3/Ga2O3 Field-Plated Modulation-Doped Field-Effect Transistors,” IEEE Electron Device Letters 40 (8), 99 (JUNE 2019) https://doi.org/10.1109/LED.2019.2921116
Z. Xia, H. Xue, C. Joishi, J. McGlone, N. K. Kalarickal, S. H. Sohel, M. Brenner, A. Arehart, S. Ringel, S. Lodha, W. Lu, and S. Rajan, “β -Ga2O3 Delta-Doped Field-Effect Transistors With Current Gain Cutoff Frequency of 27 GHz,” IEEE Electron Device Letters, 40 (7), 1052–1055 (JULY 2019) https://doi.org/10.1109/LED.2019.2920366
Y. Zhang, Z. Xia, J. McGlone, W. Sun, C. Joishi, A. R. Arehart, S. A. Ringel, and S. Rajan, “Evaluation of Low-Temperature Saturation Velocity in β‑(AlxGa1–x)2O3/Ga2O3 Modulation-Doped Field-Effect Transistors,” IEEE Transactions on Electron Devices, 66 (3), 1574–1578 (MAR 2019) https://doi.org/10.1109/TED.2018.2889573
D. A. Gleason, K. Galiano, J. L. Brown, A. M. Hilton, S. A. Ringel, A. R. Arehart, E. R. Heller, D. L. Dorsey, and J. P. Pelz, “Local trap spectroscopy on cross-sectioned AlGaN/GaN devices with in situ biasing,” Appl. Phys. Lett., 114, 053510 (FEB 2019) https://doi.org/10.1063/1.5079745
W. Sun, J. Joh, S. Krishnan, S. Pendharkar, C.M Jackson, S.A. Ringel and A.R. Arehart, “Investigation of Trap-induced Threshold Voltage Instability in GaN-on-Si MISHMETs,” IEEE Transactions on Electron Devices 66 (2), 890-895 (JAN 2019) https://doi.org/10.1109/TED.2018.2888840
Esmat Farzana, Max F. Chaiken, Thomas E. Blue, Aaron R. Arehart and Steven A. Ringel, “Impact of deep level defects induced by high energy neutron radiation in -Ga2O3,” APL Materials, 7 (2), 022502 (FEB 2019) https://doi.org/10.1063/1.5054606

2018

P. Altermatt, Zhen Xiong, QiuXiang He, WeiWei Deng, Yang Yang, Yifeng Chen, ZhiQiang Feng, Pierre J. Verlinden, Anyao Liu, Daniel H. Macdonald, Tabea Luka, Dominik Lausch, Marko Turek, Christian Hagendorf, Hannes Wagner-Mohnsen, Jonas Schön, Wolfram Kwapil , Felix Frühauf, Otwin Breitenstein, Erin E.Looney, Tonio Buonassisi, David B.Needleman, Christine M. Jackson, Aaron R. Arehart, Steven A. Ringel, Keith R. McIntosh, Malcolm D. Abbott, Ben A. Sudbury, Annika Zuschlag, Clemens Winter, Daniel Skorka, Giso Hahn, Daniel Chung, Bernhard Mitchell, Peter Geelan-Small and Thorsten Trupkek, “High-performance p-type multicrystalline silicon (mc-Si): Its characterization and projected performance in PERC solar cells,” Solar Energy 175, pp. 68-74 (2018). https://doi.org/10.1016/j.solener.2018.01.073
Daniel J. Chmielewski, Daniel. L. Lepkowski, Jacob T. Boyer, Tyler J. Grassman and Steven A. Ringel, “Comparative Study of ! 2.05 eV Lattice-matched and Metamorphic (Al)GaInP Solar Cells Grown by MOCVD,” IEEE Journal of Photovoltaics 8 (6), 1601-1607 (2018). https://doi.org/10.1109/JPHOTOV.2018.2868032
E. Farzana, H. M. Foronda, C. M. Jackson, T. Razzak, Z. Zhang, J. S. Speck, A. R. Arehart, and S. A. Ringel, “Characterization of traps in InAlN by optically and thermally stimulated deep level defect spectroscopies,” J. Appl. Phys. 124 (14), 145703 (2018). https://doi.org/10.1063/1.5050949
Joe. F. McGlone, Zhanbo Xia, Yuewei Zhang, Chandan Joishi, Saurabh Lodha, Siddharth Rajan, Steven A. Ringel, Aaron R. Arehart, “Trapping Effects in Si δ-Doped β-Ga2O3 MESFETs on an Fe-Doped β-Ga2O3 Substrate,” IEEE Electron Device Letters, vol. 39, no. 7, pp. 1042–1045, Jul. 2018. https://dx.doi.org/10.1109/LED.2018.2843344 https://dx.doi.org/10.1109/LED.2018.2843344
Kevin Galiano, J. I. Deitz, S. D. Carnevale, D. A. Gleason, P. K. Paul, Z. Zhang, B. M. McSkimming, J. S. Speck, S. A. Ringel, T. J. Grassman, A. R. Arehart, and J. P. Pelz, “Spatial correlation of the Ec-0.57 eV trap state with edge dislocations in epitaxial n-type gallium nitride”, Journal of Applied Physics 123, 224504, 2018. https://dx.doi.org/10.1063/1.5022806 ttps://dx.doi.org/10.1063/1.5022806
Esmat Farzana, Elaheh Ahmadi, James S. Speck, Aaron R. Arehart, and Steven A. Ringel, “Deep level defects in Ge-doped (010) β-Ga2O3 layers grown by plasma-assisted molecular beam epitaxy” in Journal of Applied Physics 123 (16), 161410 (2018). https://dx.doi.org/10.1063/1.5010608 (Most cited article on physical properties on semiconductors in Journal of Applied Physics in 2019 that were published in 2018. https://aip-info.org/1XPS-6GW1Q-15KIZX1W2E/cr.aspx)
C. Joishi, Z. Xia, J. McGlone, Y. Zhang, A.R. Arehart, S.A. Ringel, S. Lodha, and S. Rajan, “Effect of Buffer Iron Doping on Delta-doped b-Ga2O3 Metal Semiconductor Field Effect Transistors,” Appl. Phys. Lett 113 (12), 123501 (2018).

2017

E. Farzana, Z. Zhang, P. K. Paul, A. R. Arehart, and S. A. Ringel, "Influence of metal choice on (010) β−Ga2O3 Schottky diode properties", Appl. Phys. Lett. 110, 202102, May 2017 ( APL Editor's Pick) https://dx.doi.org/10.1063/1.4983610
J. Demuth, E. Fahrenkrug, L. Ma, T. Shodiya, J. I. Deitz, T. J. Grassman and S. Maldonado, "Electrochemical Liquid Phase Epitaxy (ec-LPE): A New Methodology for the Synthesis of Crystalline Group IV Semiconductor Epifilms," Journal of the American Chemical Society 139(20), 6960, 2017. DOI: https://dx.doi.org/10.1021/jacs.7b01968
S. Karki et al., “In Situ and Ex Situ Investigations of KF Postdeposition Treatment Effects on CIGS Solar Cells,” IEEE J. Photovolt., vol. 7, no. 2, pp. 665–669, March 2017. https://dx.doi.org/10.1109/JPHOTOV.2016.2637659
C. M. Jackson, A. R. Arehart. T. J. Grassman, B. McSkimming, J. S. Speck, and S. A. Ringel, "Impact of Surface Treatment on Interface States of ALD Al2O3/GaN Interfaces", ECS Journal of Solid State Science and Technology 6 (8), P489-P494, June 2017. https://dx.doi.org/10.1149/2.0041708jss

2016

Z. Zhang, D. Cardwell, A. Sasikumar, E. C. H. Kyle, J. Chen, E. X. Zhang, D. M. Fleetwood, R. D. Schrimpf, J. S. Speck, A. R. Arehart and S. A. Ringel, "Correlation of proton irradiation induced threshold voltage shifts to deep level traps in AlGaN/GaN heterostructures", J. Appl. Phys. 119, 165704, 2016.
T. J. Grassman, D. J. Chmielewski, S. D. Carnevale, J. A. Carlin and S. A. Ringel, "GaAs0.75P0.25/Si Dual-Junction Solar Cells Grown by MBE and MOCVD", IEEE J. Photovolt., vol. 6(1), pp. 326-331, 2016.
E. García-Tabarés, J. A. Carlin, T. J. Grassman, D. Martín, I. Rey-Stolle and S. A. Ringel, "Evolution of silicon bulk lifetime during III–V-on-Si multijunction solar cell epitaxial growth", Prog. Photovoltaics, DOI: 10.1002/pip.2703, 2016.
Z. Zhang, E. Farzana, A. R. Arehart, and S. A. Ringel, "Deep level defects throughout the bandgap of (010) b-Ga2O3 detected by optically and thermally stimulated defect spectroscopy", Appl. Phys. Lett., vol 108(5), pp. 052105, 2016.
X. Liu, C. M. Jackson, F. Wu, B. Mazumder, R. Yeluri, J. Kim, S. Keller, A. R. Arehart, S. A. Ringel, J. S. Speck, and U. K. Mishra, "Electrical and structural characterizations of crystallized Al2O3/GaN interfaces formed by in situ metalorganic chemical vapor deposition," J. Appl. Phys., vol 119, pp. 015303, JAN 7, 2016.
A. Sasikumar, A. R. Arehart, D. W. Cardwell, C. M. Jackson, W. Sun, Z. Zhang, S. A. Ringel, “Deep trap-induced dynamic on-resistance degradation in GaN-on-Si power MISHEMTs,” Microelectronics Reliability, vol. 56, pp. 37-44, JAN, 2016.
A.R. Arehart, A. Sasikumar, G.D. Via, B. Poling, E.R. Heller, S.A. Ringel, "Evidence for causality between GaN RF HEMT degradation and the Ec-0.57 eV trap in GaN," Microelectronics Reliability, vol. 56, pp.45-48, JAN, 2016.
X.S. Nguyen, X. L. Goh, L. Zhang, Z. Zhang, A. R. Arehart, S. A. Ringel, E. A. Fitzgerald, S. J. Chua, “Deep level traps in GaN LEDs grown by metal organic vapour phase epitaxy on an 8 inch Si(111) substrate,” Japanese Journal of Applied Physics, 55, 6, 2016. http://iopscience.iop.org/1347-4065/55/6/060306
J. Chen, Y. Puzyrev, E. Zhang, D. Fleetwood, R. Schrimpf, A. Arehart, S. Ringel, S. Kaun, E. Kyle, J. Speck, P. Saunier; C. Lee, S. Pantelides, “High-Field Stress, Low-Frequency Noise, and Long-term Reliability of AlGaN/GaN HEMTs,” IEEE Transactions on Device and Materials Reliability, PP, 99, 1-1, 2016. http://dx.doi.org/10.1109/TDMR.2016.2581178
J. I. Deitz, T. J. Grassman, and D. W. McComb, “Accessing High Spatial Resolution Low-Loss EELS Information without Cerenkov Radiation,” Microsc. Microanal., 22, S3, pp. 976–977, July 2016
J. I. Deitz, D. W. McComb, and T. J. Grassman, “Advancement of Heteroepitaxial III-V/Si Thin Films through Defect Characterization,” Microsc. Microanal., 22, S3, pp. 1538–1539, July 2016
J. I. Deitz, S. D. Carnevale, M. De Graef, D. W. McComb, and T. J. Grassman, “Characterization of encapsulated quantum dots via electron channeling contrast imaging,” Appl. Phys. Lett., 109, 6, p. 062101, Aug. 2016
E. Gür, Fatih Akyol, Sriram Krishnamoorthy, Siddharth Rajan, Steven A. Ringel, “Deep level defects in N-rich and In-rich InxGa1−XN: in composition dependence,” Superlattices and Microstructures, http://dx.doi.org/10.1016/j.spmi.2016.05.009, May 2016
X.S. Nguyen, HW Hou, P De Mierry, P Vennéguès, F Tendille, AR Arehart, S. A. Ringel, E. A. Fitzgerald, S. J. Chua, “Deep level traps in semi‐polar n‐GaN grown on patterned sapphire substrate by metalorganic vapor phase epitaxy,” physica status solidi (b) 253 (11), 2225-2229, Aug. 2016

2015

Z. Zhang, E. Farzana, W. Y. Sun, J. Chen, E. Zhang, D. Fleetwood, R. Schrimpf, B. McSkimming, E. Kyle, J. Speck, A. Arehart, and S. Ringel, "Thermal Stability of Deep Level Defects Induced by High Energy Proton Irradiation in n-type GaN," J. Appl. Phys., vol 118, pp. 155701, OCT, 2015.
P. K. Paul, D. W. Cardwell, C. M. Jackson, K. Galiano, K. Aryal, J. P. Pelz, S. Marsillac, S. A. Ringel, T. J. Grassman, A. R. Arehart, "Direct nm-Scale Spatial Mapping of Traps in CIGS," IEEE Journal of Photovoltaics, vol. 5(5), pp. 1482, SEP, 2015.
J. I. Deitz, S. D. Carnevale, S. A. Ringel, D. W. McComb, T. J. Grassman, “Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization,” Journal of Visualized Experiments, vol. 101, pp. e52745, JUL 17, 2015.
I. Almansouri, S. Bremner, A. Ho-Baillie, H. Mehrvarz, X. Hao, G. Conibeer, T. J. Grassman, J. A. Carlin, A. Haas, S. A. Ringel and M. A. Green. "Designing Bottom Silicon Solar Cells for Multijunction Devices," IEEE J. Photovolt., vol. 5, pp. 683-690, MAR, 2015.
A. Sasikumar, A. R. Arehart, G. D. Via, B. Winningham, B. Poling, E. Heller,
and S. A. Ringel, "Identification of an RF degradation mechanism in GaN based HEMTs triggered by midgap traps," Microelec. Reliability, vol. 55, pp. 2258-2262, 2015.
J. Chen, Y. S. Puzyrev, R. Jiang, E. X. Zhang, M. W. McCurdy, D. M. Fleetwood, R. D. Schrimpf, S. T. Pantelides, A. R. Arehart, S. A. Ringel, P. Saunier, and C. Lee, "Effects of Applied Bias and High Field Stress on the Radiation Response of GaN/AlGaN HEMTs," IEEE Transactions on Nuclear Science, Nuclear Science, vol. 62, pp. 2423-2430, 2015.
S. D. Carnevale, J. I. Deitz, J. A. Carlin, Y. N. Picard, D. W. McComb, M. De Graef, S. A. Ringel and T. J. Grassman. "Applications of Electron Channeling Contrast Imaging for the Rapid Characterization of Extended Defects in III-V/Si Heterostructures," IEEE J. Photovolt., vol. 5, pp. 676-682, MAR, 2015.
X. S. Nguyen, K. Lin, Z. Zhang, B. McSkimming, A. R. Arehart, J. S. Speck, S. A. Ringel, E. A. Fitzgerald and S. J. Chua. "Correlation of a generation-recombination center with a deep level trap in GaN," Appl. Phys. Lett., vol. 106, pp. 159903, APR 13, 2015.
Z. Zhang, A. R. Arehart, E. C. H. Kyle, J. Chen, E. X. Zhang, D. M. Fleetwood, R. D. Schrimpf, J. S. Speck and S. A. Ringel. "Proton irradiation effects on deep level states in Mg-doped p-type GaN grown by ammonia-based molecular beam epitaxy," Appl. Phys. Lett., vol. 106, pp. 022104, JAN 12, 2015.
J. I. Deitz, S. D. Carnevale, S. A. Ringel, D. W. McComb, and T. J. Grassman, “Extending characterization applications of electron channeling contrast imaging,” in 2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC), pp. 1–4, 2015
E. W. Lee et al., “Layer-transferred MoS2/GaN PN diodes,” Appl. Phys. Lett., 107, 10, p. 103505, Sep. 2015.

2014

S. D. Carnevale, J. I. Deitz, J. A. Carlin, Y. N. Picard, M. De Graef, S. A. Ringel and T. J. Grassman. "Rapid misfit dislocation characterization in heteroepitaxial III-V/Si thin films by electron channeling contrast imaging," Appl. Phys. Lett., vol. 104, pp. 232111, JUN 9, 2014.
D. J. Chmielewski, T. J. Grassman, A. M. Carlin, J. A. Carlin, A. J. Speelman and S. A. Ringel. "Metamorphic GaAsP Tunnel Junctions for High-Efficiency III-V/IV Multijunction Solar Cell Technology," IEEE J. Photovolt., vol. 4, pp. 1301-1305, SEP, 2014.
T. J. Grassman, J. A. Carlin, B. Galiana, F. Yang, M. J. Mills and S. A. Ringel. "MOCVD-Grown GaP/Si Subcells for Integrated III-V/Si Multijunction Photovoltaics," IEEE J. Photovolt., vol. 4, pp. 972-980, MAY, 2014.
Z. Zhang, C. M. Jackson, A. R. Arehart, B. Mcskimming, J. S. Speck and S. A. Ringel. "Direct Determination of Energy Band Alignments of Ni/Al2O3/GaN MOS Structures Using Internal Photoemission Spectroscopy," J Electron Mater, vol. 43, pp. 828-832, APR, 2014.

2013

T. J. Grassman, C. Ratcliff, A. M. Carlin, J. A. Carlin, L. Yang, M. J. Mills and S. A. Ringel, "III-V/GaP Epitaxy on Si for Advanced Photovoltaics and Green Light Emitters," ECS Trans. vol. 50(9), pp. 321, 2013.
A. R. Arehart, A. Sasikumar, S. Rajan, G. D. Via, B. Poling, B. Winningham, E. R. Heller, D. Brown, Y. Pei, F. Recht, U. K. Mishra and S. A. Ringel. "Direct observation of 0.57 eV trap-related RF output power reduction in AlGaN/GaN high electron mobility transistors," Solid-State Electron., vol. 80, pp. 19-22, FEB, 2013.
D. W. Cardwell, A. Sasikumar, A. R. Arehart, S. W. Kaun, J. Lu, S. Keller, J. S. Speck, U. K. Mishra, S. A. Ringel and J. P. Pelz. "Spatially-resolved spectroscopic measurements of E-c-0.57 eV traps in AlGaN/GaN high electron mobility transistors," Appl. Phys. Lett., vol. 102, pp. 193509, MAY 13, 2013.
T. J. Grassman, J. A. Carlin, B. Galiana, L. -. Yang, F. Yang, M. J. Mills and S. A. Ringel. "Nucleation-related defect-free GaP/Si(100) heteroepitaxy via metal-organic chemical vapor deposition," Appl. Phys. Lett., vol. 102, pp. 142102, APR 8, 2013.
C. M. Jackson, A. R. Arehart, E. Cinkilic, B. McSkimming, J. S. Speck and S. A. Ringel. "Interface trap characterization of atomic layer deposition Al2O3/GaN metal-insulator-semiconductor capacitors using optically and thermally based deep level spectroscopies," J. Appl. Phys., vol. 113, pp. 204505, MAY 28, 2013.
R. D. Long, C. M. Jackson, J. Yang, A. Hazeghi, C. Hitzman, S. Majety, A. R. Arehart, Y. Nishi, T. P. Ma, S. A. Ringel and P. C. McIntyre. "Interface trap evaluation of Pd/Al2O3/GaN metal oxide semiconductor capacitors and the influence of near-interface hydrogen," Appl. Phys. Lett., vol. 103, pp. 201607, NOV 11, 2013.
A. Sasikumar, A. R. Arehart, S. Martin-Horcajo, M. F. Romero, Y. Pei, D. Brown, F. Recht, M. A. di Forte-Poisson, F. Calle, M. J. Tadjer, S. Keller, S. P. DenBaars, U. K. Mishra and S. A. Ringel. "Direct comparison of traps in InAlN/GaN and AlGaN/GaN high electron mobility transistors using constant drain current deep level transient spectroscopy," Appl. Phys. Lett., vol. 103, pp. 033509, JUL 15, 2013.
Z. Zhang, A. R. Arehart, E. Cinkilic, J. Chen, E. X. Zhang, D. M. Fleetwood, R. D. Schrimpf, B. McSkimming, J. S. Speck and S. A. Ringel. "Impact of proton irradiation on deep level states in n-GaN," Appl. Phys. Lett., vol. 103, pp. 042102, JUL 22, 2013.

2012

D. W. Cardwell, A. R. Arehart, C. Poblenz, Y. Pei, J. S. Speck, U. K. Mishra, S. A. Ringel and J. P. Pelz. "Nm-scale measurements of fast surface potential transients in an AlGaN/GaN high electron mobility transistor," Appl. Phys. Lett., vol. 100, pp. 193507, MAY 7, 2012.
E. Gur, G. Tabares, A. Arehart, J. M. Chauveau, A. Hierro and S. A. Ringel. "Deep levels in a-plane, high Mg-content MgxZn1-xO epitaxial layers grown by molecular beam epitaxy," J. Appl. Phys., vol. 112, pp. 123709, DEC 15, 2012.
A. Sasikumar, A. Arehart, S. Kolluri, M. H. Wong, S. Keller, S. P. DenBaars, J. S. Speck, U. K. Mishra and S. A. Ringel. "Access-Region Defect Spectroscopy of DC-Stressed N-Polar GaN MIS-HEMTs," IEEE Electron Device Lett., vol. 33, pp. 658-660, MAY, 2012.
Z. Zhang, C. A. Hurni, A. R. Arehart, J. S. Speck and S. A. Ringel. "Influence of V/III growth flux ratio on trap states in m-plane GaN grown by ammonia-based molecular beam epitaxy," Appl. Phys. Lett., vol. 101, pp. 152104, OCT 8, 2012.
Z. Zhang, C. A. Hurni, A. R. Arehart, J. Yang, R. C. Myers, J. S. Speck and S. A. Ringel. "Deep traps in nonpolar m-plane GaN grown by ammonia-based molecular beam epitaxy," Appl. Phys. Lett., vol. 100, pp. 052114, JAN 30, 2012.

2011

A. R. Arehart, A. A. Allerman and S. A. Ringel. "Electrical characterization of n-type Al0.30Ga0.70N Schottky diodes," J. Appl. Phys., vol. 109, pp. 114506, JUN 1, 2011.
A. R. Arehart, A. C. Malonis, C. Poblenz, Y. Pei, J. S. Speck, U. K. Mishra and S. A. Ringel. "Next generation defect characterization in nitride HEMTs," Physica Status Solidi C, vol. 8, 2011.
M. Gonzalez, A. M. Carlin, C. L. Dohrman, E. A. Fitzgerald and S. A. Ringel. "Determination of bandgap states in p-type In0.49Ga0.51P grown on SiGe/Si and GaAs by deep level optical spectroscopy and deep level transient spectroscopy," J. Appl. Phys., vol. 109, pp. 063709, MAR 15, 2011.
E. Gur, Z. Zhang, S. Krishnamoorthy, S. Rajan and S. A. Ringel. "Detailed characterization of deep level defects in InGaN Schottky diodes by optical and thermal deep level spectroscopies", Appl. Phys. Lett., vol. 99, pp. 229906, NOV 28, 2011.
D. N. Nath, E. Guer, S. A. Ringel and S. Rajan. "Growth model for plasma-assisted molecular beam epitaxy of N-polar and Ga-polar InxGa1-xN," J. Vac. Sci. Technol. B, vol. 29, pp. 021206, MAR, 2011.
C. Ratcliff, T. J. Grassman, J. A. Carlin and S. A. Ringel. "High temperature step-flow growth of gallium phosphide by molecular beam epitaxy and metalorganic chemical vapor deposition," Appl. Phys. Lett., vol. 99, pp. 141905, OCT 3, 2011.
K. Swaminathan, T. J. Grassman, L. -. Yang, Q. Gu, M. J. Mills and S. A. Ringel. "Optically-aligned visible/near-infrared dual-band photodetector materials and devices on GaAs using metamorphic epitaxy," J. Appl. Phys., vol. 110, pp. 063109, SEP 15, 2011.
K. Swaminathan, L. -. Yang, T. J. Grassman, G. Tabares, A. Guzman, A. Hierro, M. J. Mills and S. A. Ringel. "Metamorphic In0.20Ga0.80As p-i-n photodetectors grown on GaAs substrates for near infrared applications," Opt. Express, vol. 19, pp. 7280-7288, APR 11, 2011.
K. H. Tan, S. Wicaksono, W. K. Loke, D. Li, S. F. Yoon, E. A. Fitzgerald, S. A. Ringel and J. S. Harris Jr. "Molecular beam epitaxy grown GaNAsSb 1 eV photovoltaic cell," J. Cryst. Growth, vol. 335, pp. 66-69, NOV 15, 2011.

2010

A. R. Arehart, T. Homan, M. H. Wong, C. Poblenz, J. S. Speck and S. A. Ringel. "Impact of N- and Ga-face polarity on the incorporation of deep levels in n-type GaN grown by molecular beam epitaxy," Appl. Phys. Lett., vol. 96, pp. 242112, JUN 14, 2010.
A. R. Arehart, C. Poblenz, J. S. Speck and S. A. Ringel. "Effect of nitrogen plasma power on defect levels in Ni/n-GaN Schottky diodes grown by molecular beam epitaxy," J. Appl. Phys., vol. 107, pp. 054518, MAR 1, 2010.
T. J. Grassman, M. R. Brenner, M. Gonzalez, A. M. Carlin, R. R. Unocic, R. R. Dehoff, M. J. Mills and S. A. Ringel. "Characterization of Metamorphic GaAsP/Si Materials and Devices for Photovoltaic Applications," IEEE Trans. Electron Devices, vol. 57, pp. 3361-3369, DEC, 2010.
D. N. Nath, E. Gur, S. A. Ringel and S. Rajan. "Molecular beam epitaxy of N-polar InGaN," Appl. Phys. Lett., vol. 97, pp. 071903, AUG 16, 2010.
J. H. Warner, C. D. Cress, S. R. Messenger, R. J. Walters, S. A. Ringel and J. Park. "A Deep Level Transient Spectroscopy Study of Electron and Proton Irradiated p(+) n GaAs Diodes," IEEE Trans. Nucl. Sci., vol. 57, pp. 1940-1945, AUG, 2010.
C. K. Yang, P. Roblin, F. De Groote, S. A. Ringel, S. Rajan, J. P. Teyssier, C. Poblenz, Y. Pei, J. Speck and U. K. Mishra. "Pulsed-IV Pulsed-RF Cold-FET Parasitic Extraction of Biased AlGaN/GaN HEMTs Using Large Signal Network Analyzer," IEEE Trans. Microwave Theory Tech., vol. 58, pp. 1077-1088, MAY, 2010.

2009

T. J. Grassman, M. R. Brenner, S. Rajagopalan, R. Unocic, R. Dehoff, M. Mills, H. Fraser and S. A. Ringel. "Control and elimination of nucleation-related defects in GaP/Si(001) heteroepitaxy," Appl. Phys. Lett., vol. 94, pp. 232106, JUN 8, 2009.
M. K. Hudait, M. Brenner and S. A. Ringel. "Metamorphic In0.7Al0.3As/In0.69Ga0.31As thermophotovoltaic devices grown on graded InAsyP1-y buffers by molecular beam epitaxy," Solid-State Electron., vol. 53, pp. 102-106, JAN, 2009.
M. K. Hudait, Y. Lin and S. A. Ringel. "Strain relaxation properties of InAsyP1-y metamorphic materials grown on InP substrates," J. Appl. Phys., vol. 105, pp. 061643, MAR 15, 2009.

2008

A. R. Arehart, A. Corrion, C. Poblenz, J. S. Speck, U. K. Mishra, S. P. DenBaars and S. A. Ringel. "Comparison of deep level incorporation in ammonia and rf-plasma assisted molecular beam epitaxy n-GaN films," Physica Status Solidi C, vol. 5, pp. 1750-1752, 2008.
A. R. Arehart, A. Corrion, C. Poblenz, J. S. Speck, U. K. Mishra and S. A. Ringel. "Deep level optical and thermal spectroscopy of traps in n-GaN grown by ammonia molecular beam epitaxy," Appl. Phys. Lett., vol. 93, pp. 112101, SEP 15, 2008.
A. Armstrong, J. Caudill, A. Corrion, C. Poblenz, U. K. Mishra, J. S. Speck and S. A. Ringel. "Characterization of majority and minority carrier deep levels in p-type GaN : Mg grown by molecular beam epitaxy using deep level optical spectroscopy," J. Appl. Phys., vol. 103, pp. 063722, MAR 15, 2008.
Y. Lin, A. R. Arehart, A. M. Carlin and S. A. Ringel. "Separation of bulk and surface electron transport in metamorphic InAs layers using quantitative mobility spectrum analysis," Appl. Phys. Lett., vol. 93, pp. 062109, AUG 11, 2008.
P. E. Smith, M. Lueck, S. A. Ringel and L. J. Brillson. "Atomic diffusion and interface electronic structure at In0.49Ga0.51P/GaAs heterojunctions," J. Vac. Sci. Technol. B, vol. 26, pp. 89-95, JAN, 2008.

2007

A. Armstrong, A. Corrion, C. Poblenz, U. K. Mishra, J. S. Speck and S. A. Ringel. "Comparison of deep level spectra in p-type and n-type GaN grown by molecular beam epitaxy", Phys. Status Solidi B-Basic Solid State Phys., vol. 244, pp. 4692-4692, DEC, 2007.
Y. Lin, J. A. Carlin, A. R. Arehart, A. M. Carlin and S. A. Ringel. "High-mobility two-dimensional electron gas in InAlAs/InAs heterostructures grown on virtual InAs substrates by molecular-beam epitaxy," Appl. Phys. Lett., vol. 90, pp. 012115, JAN 1, 2007.
D. Liu, M. Hudait, Y. Lin, H. Kim, S. A. Ringel and W. Lu. "Gate length scaling study of InAlAs/InGaAs/InAsP composite channel HEMTs," Solid-State Electron., vol. 51, pp. 838-841, JUN, 2007.
H. L. Mosbacker, S. El Hage, M. Gonzalez, S. A. Ringel, M. Hetzer, D. C. Look, G. Cantwell, J. Zhang, J. J. Song and L. J. Brillson. "Role of subsurface defects in metal-ZnO(0001) Schottky barrier formation," J. Vac. Sci. Technol. B, vol. 25, pp. 1405-1411, JUL-AUG, 2007.
P. E. Smith, M. Lueck, S. A. Ringel and L. J. Brillson. "Atomic diffusion and electronic structure in Al0.52In0.48P/GaAs heterostructures," J. Vac. Sci. Technol. B, vol. 25, pp. 1916-1921, NOV, 2007.

2006

A. R. Arehart, B. Moran, J. S. Speck, U. K. Mishra, S. P. DenBaars and S. A. Ringel. "Effect of threading dislocation density on Ni/n-GaN Schottky diode I-V characteristics," J. Appl. Phys., vol. 100, pp. 023709, JUL 15, 2006.
A. Armstrong, A. Chakraborty, J. S. Speck, S. P. DenBaars, U. K. Mishra and S. A. Ringel. "Quantitative observation and discrimination of AlGaN- and GaN-related deep levels in AlGaN/GaN heterostructures using capacitance deep level optical spectroscopy," Appl. Phys. Lett., vol. 89, pp. 262116, DEC 25, 2006.
A. Armstrong, C. Poblenz, D. Green, U. Mishra, J. Speck and S. Ringel. "Impact of substrate temperature on the incorporation of carbon-related defects and mechanism for semi-insulating behavior in GaN grown by molecular beam epitaxy," Appl. Phys. Lett., vol. 88, pp. 082114, FEB 20, 2006.
M. Gao, S. T. Bradley, Y. Cao, D. Jena, Y. Lin, S. A. Ringel, J. Hwang, W. J. Schaff and L. J. Brillson. "Compositional modulation and optical emission in AlGaN epitaxial films," J. Appl. Phys., vol. 100, pp. 103512, NOV 15, 2006.
M. Gonzalez, C. L. Andre, R. J. Walters, S. R. Messenger, J. H. Warner, J. R. Lorentzen, A. J. Pitera, E. A. Fitzgerald and S. A. Ringel. "Deep level defects in proton radiated GaAs grown on metamorphic SiGe/Si substrates," J. Appl. Phys., vol. 100, pp. 034503, AUG 1, 2006.
M. Gonzalez, C. L. Andre, R. J. Walters, S. R. Messenger, J. H. Warner, J. R. Lorentzen, A. J. Pitera, E. J. Fitzgerald and S. A. Ringel. "Deep level defects in proton radiated GaAs grown on metamorphic SiGe/Si substrates (vol 100, pg 034503, 2006)," J. Appl. Phys., vol. 100, pp. 119901, DEC 1, 2006.
M. K. Hudait, Y. Lin, P. M. Sinha, J. R. Lindemuth and S. A. Ringel. "Carrier compensation and scattering mechanisms in Si-doped InAsyP1-y layers grown on InP substrates using intermediate InAsyP1-y step-graded buffers," J. Appl. Phys., vol. 100, pp. 063705, SEP 15, 2006.
O. Kwon, J. J. Boeckl, M. L. Lee, A. J. Pitera, E. A. Fitzgerald and S. A. Ringel. "Monolithic integration of AlGaInP laser diodes on SiGe/Si substrates by molecular beam epitaxy," J. Appl. Phys., vol. 100, pp. 013103, JUL 1, 2006.
D. Liu, M. Hudait, Y. Lin, H. Kim, S. Ringel and W. Lu. "In0.53Ga0.47As/InAs0.3P0.7 composite channel high electron mobility transistors," Electron. Lett., vol. 42, pp. 307-309, MAR 2, 2006.
M. Lueck, C. Andre, A. Pitera, M. Lee, E. Fitzgerald and S. Ringel. "Dual junction GaInP/GaAs solar cells grown on metamorphic SiGe/Si substrates with high open circuit voltage," IEEE Electron Device Lett., vol. 27, pp. 142-144, MAR, 2006.

2005

C. Andre, J. Carlin, J. Boeckl, D. Wilt, M. Smith, A. Pitera, M. Lee, E. Fitzgerald and S. Ringel. "Investigations of high-performance GaAs solar cells grown on Ge-Si1-xGex-Si substrates," IEEE Trans. Electron Devices, vol. 52, pp. 1055-1060, JUN, 2005.
C. Andre, D. Wilt, A. Pitera, M. Lee, E. Fitzgerald and S. Ringel. "Impact of dislocation densities on n(+)/p and p(+)/n junction GaAs diodes and solar cells on SiGe virtual substrates," J. Appl. Phys., vol. 98, pp. 014502, JUL 1, 2005.
A. Armstrong, A. Arehart, D. Green, J. Speck, U. Mishra and S. Ringel. "A novel method to investigate defect states in MBE grown highly resistive GaN doped with C and Si," Physica Status Solidi C, vol. 2, pp. 2411-2414, 2005.
A. Armstrong, A. Arehart, D. Green, U. Mishra, J. Speck and S. Ringel. "Impact of deep levels on the electrical conductivity and luminescence of gallium nitride codoped with carbon and silicon," J. Appl. Phys., vol. 98, pp. 053704, SEP 1, 2005.
A. Armstrong, A. Arehart and S. Ringel. "A method to determine deep level profiles in highly compensated, wide band gap semiconductors," J. Appl. Phys., vol. 97, pp. 083529, APR 15, 2005.
M. Gao, Y. Lin, S. Bradley, S. Ringel, J. Hwang, W. Schaff and L. Brillson. "Spontaneous compositional superlattice and band-gap reduction in Si-doped AlxGa1-xN epilayers," Appl. Phys. Lett., vol. 87, pp. 191905, NOV 7, 2005.
M. Hudait, Y. Lin, S. Goss, P. Smith, S. Bradley, L. Brillson, S. Johnston, R. Ahrenkiel and S. Ringel. "Evidence of interface-induced persistent photoconductivity in InP/In0.53Ga0.47As/InP double heterostructures grown by molecular-beam epitaxy," Appl. Phys. Lett., vol. 87, pp. 032106, JUL 18, 2005.
O. Kwon, J. Boeckl, M. Lee, A. Pitera, E. Fitzgerald and S. Ringel. "Growth and properties of AlGaInP resonant cavity light emitting diodes on Ge/SiGe/Si substrates," J. Appl. Phys., vol. 97, pp. 034504, FEB 1, 2005.
O. Kwon, Y. Lin, J. Boeckl and S. Ringel. "Growth and properties of digitally-alloyed AlGaInP by solid source molecular beam epitaxy," J Electron Mater, vol. 34, pp. 1301-1306, OCT, 2005.
Y. Lin, M. Hudait, S. Johnston, R. Ahrenkiel and S. Ringel. "Photoconductivity decay in metamorphic InAsP/InGaAs double heterostructures grown on InAsyP1-y compositionally step-graded buffers," Appl. Phys. Lett., vol. 86, pp. 071908, FEB 14, 2005.
P. Smith, S. Goss, M. Gao, M. Hudait, Y. Lin, S. Ringel and L. Brillson. "Atomic diffusion and band lineups at In0.53Ga0.47As-on-InP heterointerfaces," J. Vac. Sci. Technol. B, vol. 23, pp. 1832-1837, JUL-AUG, 2005.
C. Tivarus, J. Pelz, M. Hudait and S. Ringel. "Spatial resolution of ballistic electron emission microscopy measured on metal/quantum-well Schottky contacts," Appl. Phys. Lett., vol. 87, pp. 182105, OCT 31, 2005.
C. Tivarus, J. Pelz, M. Hudait and S. Ringel. "Direct measurement of quantum confinement effects at metal to quantum-well nanocontacts," Phys. Rev. Lett., vol. 94, pp. 206803, MAY 27, 2005.

2004

C. Andre, J. Boeckl, D. Wilt, A. Pitera, M. Lee, E. Fitzgerald, B. Keyes and S. Ringel. "Impact of dislocations on minority carrier electron and hole lifetimes in GaAs grown on metamorphic SiGe substrates," Appl. Phys. Lett., vol. 84, pp. 3447-3449, MAY 3, 2004.
A. Armstrong, A. Arehart, B. Moran, S. DenBaars, U. Mishra, J. Speck and S. Ringel. "Impact of carbon on trap states in n-type GaN grown by metalorganic chemical vapor deposition," Appl. Phys. Lett., vol. 84, pp. 374-376, JAN 19, 2004.
M. Hudait, Y. Lin, M. Palmisiano, C. Tivarus, J. Pelz and S. Ringel. "Comparison of mixed anion, InAsyP1-y and mixed cation, InxAl1-xAs metamorphic buffers grown by molecular beam epitaxy on (100)InP substrates," J. Appl. Phys., vol. 95, pp. 3952-3960, APR 15, 2004.
P. Smith, S. Goss, S. Bradley, M. Hudait, Y. Lin, S. Ringel and L. Brillson. "Atomic layer diffusion and electronic structure at In0.53Ga0.47As/InP interfaces," J. Vac. Sci. Technol. B, vol. 22, pp. 554-559, MAR-APR, 2004.

2003

C. Andre, J. Boeckl, C. Leitz, M. Currie, T. Langdo, E. Fitzgerald and S. Ringel. "Low-temperature GaAs films grown on Ge and Ge/SiGe/Si substrates," J. Appl. Phys., vol. 94, pp. 4980-4985, OCT 15, 2003.
M. Hudait, Y. Lin, M. Palmisiano and S. Ringel. "0.6-eV bandgap In0.69Ga0.31As thermophotovoltaic devices grown on InAsyP1-y step-graded buffers by molecular beam epitaxy," IEEE Electron Device Lett., vol. 24, pp. 538-540, SEP, 2003.
M. Hudait, Y. Lin, D. Wilt, J. Speck, C. Tivarus, E. Heller, J. Pelz and S. Ringel. "High-quality InAsyP1-y step-graded buffer by molecular-beam epitaxy," Appl. Phys. Lett., vol. 82, pp. 3212-3214, MAY 12, 2003.
M. Hudait, Y. Lin, D. Wilt, F. Wu, J. Speck, C. Tivarus, E. Heller, J. Pelz and S. Ringel. "High-quality InAsyP1-y step-graded buffer by molecular-beam epitaxy (vol 82, pg 3212, 2003)," Appl. Phys. Lett., vol. 83, pp. 587-587, JUL 21, 2003.
O. Kwon, M. Jazwiecki, R. Sacks and S. Ringel. "High-performance, metamorphic InxGa1-xAs tunnel diodes grown by molecular beam epitaxy," IEEE Electron Device Lett., vol. 24, pp. 613-615, OCT, 2003.

2002

A. Hierro, A. Arehart, B. Heying, M. Hansen, U. Mishra, S. DenBaars, J. Speck and S. Ringel. "Impact of Ga/N flux ratio on trap states in n-GaN grown by plasma-assisted molecular-beam epitaxy," Appl. Phys. Lett., vol. 80, pp. 805-807, FEB 4, 2002.
M. Hudait, C. Andre, O. Kwon, M. Palmisiano and S. Ringel. "High-performance In0.53Ga0.47 as thermophotovoltaic devices grown by solid source molecular beam epitaxy," IEEE Electron Device Lett., vol. 23, pp. 697-699, DEC, 2002.
R. Kaplar, S. Ringel, S. Kurtz, J. Klem and A. Allerman. "Deep-level defects in InGaAsN grown by molecular-beam epitaxy," Appl. Phys. Lett., vol. 80, pp. 4777-4779, JUN 24, 2002.
S. Ringel, J. Carlin, C. Andre, M. Hudait, M. Gonzalez, D. Wilt, E. Clark, P. Jenkins, D. Scheiman, A. Allerman, E. Fitzgerald and C. Leitz. "Single-junction InGaP/GaAs solar cells grown on Si substrates with SiGe buffer layers," Prog. Photovoltaics, vol. 10, pp. 417-426, SEP, 2002.

2001

J. Carlin, S. Ringel, A. Fitzgerald and M. Bulsara. "High-lifetime GaAs on Si using GeSi buffers and its potential for space photovoltaics," Solar Energy Mater. Solar Cells, vol. 66, pp. 621-630, FEB, 2001.
A. Hierro, A. Arehart, B. Heying, M. Hansen, J. Speck, U. Mishra, S. DenBaars and S. Ringel. "Capture kinetics of electron traps in MBE-grown n-GaN," Phys. Status Solidi B-Basic Res., vol. 228, pp. 309-313, NOV, 2001.
A. Hierro, M. Hansen, J. Boeckl, L. Zhao, J. Speck, U. Mishra, S. DenBaars and S. Ringel. "Carrier trapping and recombination at point defects and dislocations in MOCVD n-GaN," Phys. Status Solidi B-Basic Res., vol. 228, pp. 937-946, DEC, 2001.
R. Kaplar, A. Arehart, S. Ringel, A. Allerman, R. Sieg and S. Kurtz. "Deep levels and their impact on generation current in Sn-doped InGaAsN," J. Appl. Phys., vol. 90, pp. 3405-3408, OCT 1, 2001.
R. Kaplar, D. Kwon, S. Ringel, A. Allerman, S. Kurtz, E. Jones and R. Sieg. "Deep levels in p- and n-type InGaAsN for high-efficiency multi-junction III-V solar cells," Solar Energy Mater. Solar Cells, vol. 69, pp. 85-91, AUG, 2001.

2000

J.A. Carlin, S.A. Ringel, J.J. Boeckl, R.J. Kaplar and E.A. Fitzgerald, “High lifetime GaAs on Si using GeSi buffers and its potential for space applications,” Solar Energy Materials and Solar Cells, vol. 66, pp. 621-630, 2000.
J. Carlin, S. Ringel, E. Fitzgerald and M. Bulsara. "High quality GaAs growth by MBE on Si using GeSi buffers and prospects for space photovoltaics," Prog. Photovoltaics, vol. 8, pp. 323-332, MAY-JUN, 2000.
J. Carlin, S. Ringel, E. Fitzgerald, M. Bulsara and B. Keyes. "Impact of GaAs buffer thickness on electronic quality of GaAs grown on graded Ge/GeSi/Si substrates," Appl. Phys. Lett., vol. 76, pp. 1884-1886, APR 3, 2000.
A. Hierro, D. Kwon, S. Ringel, M. Hansen, U. Mishra, S. DenBaars and J. Speck. "Deep levels in n-type Schottky and p(+)-n homojunction GaN diodes," MRS Internet J. Nitride Semicond. Res., vol. 5, pp. W11.80, 2000.
A. Hierro, D. Kwon, S. Ringel, M. Hansen, J. Speck, U. Mishra and S. DenBaars. "Optically and thermally detected deep levels in n-type Schottky and p(+)-n GaN diodes," Appl. Phys. Lett., vol. 76, pp. 3064-3066, MAY 22, 2000.
A. Hierro, D. Kwon, S. Ringel, S. Rubini, E. Pelucchi and A. Franciosi. "Photocapacitance study of bulk deep levels in ZnSe grown by molecular-beam epitaxy," J. Appl. Phys., vol. 87, pp. 730-738, JAN 15, 2000.
A. Hierro, S. Ringel, M. Hansen, J. Speck, U. Mishra and S. DenBaars. "Hydrogen passivation of deep levels in n-GaN," Appl. Phys. Lett., vol. 77, pp. 1499-1501, SEP 4, 2000.

1999

A. Hierro, D. Kwon, S. Goss, L. Brillson, S. Ringel, S. Rubini, E. Pelucchi and A. Franciosi. "Evidence for a dominant midgap trap in n-ZnSe grown by molecular beam epitaxy," Appl. Phys. Lett., vol. 75, pp. 832-834, AUG 9, 1999.
D. Kwon, R. Kaplar, S. Ringel, A. Allerman, S. Kurtz and E. Jones. "Deep levels in p-type InGaAsN lattice matched to GaAs," Appl. Phys. Lett., vol. 74, pp. 2830-2832, MAY 10, 1999.
S. Ringel and P. Grillot. "Electronic properties and deep levels in germanium-silicon," Germanium Silicon: Physics and Materials, vol. 56, pp. 293-346, 1999.
R. Sacks, L. Qin, M. Jazwiecki, S. Ringel, M. Clevenger, D. Wilt and M. Goorsky. "Growth and characterization of epitaxial FexAl1-x/(In,Al)As/InP and III-V/FexAl1-x/(In,Al)As/InP structures," J. Vac. Sci. Technol. B, vol. 17, pp. 1289-1293, MAY-JUN, 1999.
Q. Xu, J. Hsu, J. Carlin, R. Sieg, J. Boeckl and S. Ringel. "Topographic and electronic studies of wedge-shape surface defects on AlGaAs/GaAs films grown on Ge substrates," Appl. Phys. Lett., vol. 75, pp. 2111-2113, OCT 4, 1999.

1998

B. Anderson, L. Pelz, S. Ringel, B. Clymer and S. Collins. "Photonics laboratory with emphasis on technical diversity," IEEE Trans. Educ., vol. 41, pp. 194-202, AUG, 1998.
J. Carlin, S. Ringel, R. Sacks and K. Yap. "Role of Al content on surface structure evolution of low temperature AlxGa1-xAs and its effect an critical thickness," J. Vac. Sci. Technol. B, vol. 16, pp. 1372-1376, MAY-JUN, 1998.
S. Ringel and B. Chatterjee. "Electrical deactivation of interstitial Zn in heteroepitaxial InP by hydrogen and its effect on electronic properties," J. Appl. Phys., vol. 83, pp. 5904-5912, JUN 1, 1998.
R. Sieg, J. Carlin, J. Boeckl, S. Ringel, M. Currie, S. Ting, T. Langdo, G. Taraschi, E. Fitzgerald and B. Keyes. "High minority-carrier lifetimes in GaAs grown on low-defect-density Ge/GeSi/Si substrates," Appl. Phys. Lett., vol. 73, pp. 3111-3113, NOV 23, 1998.
R. Sieg, S. Ringel, S. Ting, E. Fitzgerald and R. Sacks. "Anti-phase domain-free growth of GaAs on offcut (001) Ge wafers by molecular beam epitaxy with suppressed Ge outdiffusion," J Electron Mater, vol. 27, pp. 900-907, JUL, 1998.
R. Sieg, S. Ringel, S. Ting, S. Samavedam, M. Currie, T. Langdo and E. Fitzgerald. "Toward device-quality GaAs growth by molecular beam epitaxy on offcut Ge/Si1-xGex/Si substrates," J. Vac. Sci. Technol. B, vol. 16, pp. 1471-1474, MAY-JUN, 1998.
S. Ting, E. Fitzgerald, R. Sieg and S. Ringel. "Range of defect morphologies on GaAs grown on offcut (001) Ge substrates," J Electron Mater, vol. 27, pp. 451-461, MAY, 1998.
Q. Xu, J. Hsu, S. Ting, E. Fitzgerald, R. Sieg and S. Ringel. "Scanning force microscopy studies of GaAs films grown on offcut Ge substrates," J Electron Mater, vol. 27, pp. 1010-1016, SEP, 1998.

1997

R. Hoffman, N. Fatemi, V. Weizer, P. Jenkins, M. Stan, S. Ringel, D. Scheiman, D. Wilt and D. Brinker. "High beginning-of-life efficiency p/n InP solar cells," Prog. Photovoltaics, vol. 5, pp. 415-422, NOV-DEC, 1997.
S. Ringel. "Hydrogen-extended defect interactions in heteroepitaxial InP materials and devices," Solid-State Electron., vol. 41, pp. 359-380, MAR, 1997.
S. Ringel, B. Chatterjee and R. Hoffman. "Hydrogen passivation of interstitial Zn defects in hetero-epitaxial InP cell structures and influence on device characteristics," Prog. Photovoltaics, vol. 5, pp. 423-431, NOV-DEC, 1997.
R. Sieg, R. Sacks and S. Ringel. "Application of pyrometric interferometry to the in situ monitoring of In0.52Al0.48As, In0.53Ga0.47As, and quaternary alloy growth on InP substrates," J. Cryst. Growth, vol. 175, pp. 256-261, MAY, 1997.

1996

B. Chatterjee and S. Ringel. "Effect of extended defects on the formation and dissociation kinetics of Zn-H complexes in heteroepitaxial p-type InP layers," Appl. Phys. Lett., vol. 69, pp. 839-841, AUG 5, 1996.
B. Chatterjee, S. Ringel and R. Hoffmann. "Hydrogen passivation of n(+)p and p(+)n heteroepitaxial InP solar cell structures," Prog. Photovoltaics, vol. 4, pp. 91-100, MAR-APR, 1996.
P. Grillot and S. Ringel. "Identification of compositionally invariant deep levels introduced by plastic strain in epitaxial Ge0.30Si0.70 and deformed bulk Si," Appl. Phys. Lett., vol. 69, pp. 2110-2112, SEP 30, 1996.
P. Grillot, S. Ringel and E. Fitzgerald. "Effect of composition on deep levels in heteroepitaxial GexS1-x layers and evidence for dominant intrinsic recombination-generation in relaxed Ge layers on Si," J Electron Mater, vol. 25, pp. 1028-1036, JUL, 1996.
P. Grillot, S. Ringel, J. Michel and E. Fitzgerald. "Structural, electronic, and luminescence investigation of strain-relaxation induced electrical conductivity type conversion in GeSi/Si heterostructures," J. Appl. Phys., vol. 80, pp. 2823-2832, SEP 1, 1996.
R. Sacks, R. Sieg and S. Ringel. "Investigation of the accuracy of pyrometric interferometry in determining AlxGa1-xAs growth rates and compositions," J. Vac. Sci. Technol. B, vol. 14, pp. 2157-2162, MAY-JUN, 1996.
R. Sieg and S. Ringel. "Reabsorption, band-gap narrowing, and the reconciliation of photoluminescence spectra with electrical measurements for epitaxial n-InP," J. Appl. Phys., vol. 80, pp. 448-458, JUL 1, 1996.
R. Sieg, R. Sacks, P. Grillot and S. Ringel. "Improved substrate temperature stability during molecular beam epitaxy growth using indium free mounting of small substrates of various shapes," J. Vac. Sci. Technol. A-Vac. Surf. Films, vol. 14, pp. 3283-3287, NOV-DEC, 1996.

1995

B. Chatterjee and S. A. Ringel. "Hydrogen Passivation and its Effects on Carrier Trapping by Dislocations in Inp/gaas Heterostructures," J. Appl. Phys., vol. 77, pp. 3885-3898, APR 15, 1995.
P. N. Grillot, S. A. Ringel, E. A. Fitzgerald, G. P. Watson and Y. H. Xie. "Electron Trapping Kinetics at Dislocations in Relaxed Ge0.3si0.7/si Heterostructures," J. Appl. Phys., vol. 77, pp. 3248-3256, APR 1, 1995.
P. N. Grillot, S. A. Ringel, E. A. Fitzgerald, G. P. Watson and Y. H. Xie. "Minority- and Majority-Carrier Trapping in Strain-Relaxed Ge0.3si0.7/si Heterostructure Diodes Grown by Rapid Thermal Chemical-Vapor-Deposition," J. Appl. Phys., vol. 77, pp. 676-685, JAN 15, 1995.
R. A. Mena, S. E. Schacham, E. J. Haugland, S. A. Alterovitz, S. B. Bibyk and S. A. Ringel. "Subband Quantum Scattering Times for AlGaAs/GaAs obtained using Digital Filtering," J. Appl. Phys., vol. 78, pp. 3940-3944, SEP 15, 1995.
R. A. Mena, S. E. Schacham, E. J. Haugland, S. A. Alterovitz, P. G. Young, S. B. Bibyk and S. A. Ringel. "Characterization of the Transport-Properties of Channel Delta-Doped Structures by Light-Modulated Shubnikov-De Haas Measurements," J. Appl. Phys., vol. 78, pp. 6626-6632, DEC 1, 1995.
R. M. Sieg, B. Chatterjee and S. A. Ringel. "Evidence for Enhanced Zinc Interstitial Concentration in Strain-Relaxed Heteroepitaxial Indium-Phosphide," Appl. Phys. Lett., vol. 66, pp. 3108-3110, JUN 5, 1995.

1994

B. Chatterjee, S. A. Ringel, R. Sieg, R. Hoffman and I. Weinberg. "Hydrogen Passivation of Dislocations in Inp on Gaas Heterostructures," Appl. Phys. Lett., vol. 65, pp. 58-60, JUL 4, 1994.

1991

S. A. Ringel and A. Rohatgi. "The Effects of Trap-Induced Lifetime Variations on the Design and Performance of High-Efficiency GaAs Solar-Cells," IEEE Trans. Electron Devices, vol. 38, pp. 2402-2409, NOV, 1991.
S. A. Ringel, A. W. Smith, M. H. MacDougal and A. Rohatgi. "The Effects of Cdcl2 on the Electronic-Properties of Molecular-Beam Epitaxially Grown Cdte/cds Heterojunction Solar-Cells," J. Appl. Phys., vol. 70, pp. 881-889, JUL 15, 1991.
A. Rohatgi, R. Sudharsanan, S. A. Ringel and M. H. MacDougal. "Growth and Process Optimization of Cdte and Cdznte Polycrystalline Films for High-Efficiency Solar-Cells," Solar Cells, vol. 30, pp. 109-122, MAY, 1991.

1990

S. A. Ringel, R. Sudharsanan, A. Rohatgi and W. B. Carter. "A Study of Polycrystalline Cd(zn, Mn)te/cds Films and Interfaces," J Electron Mater, vol. 19, pp. 259-263, MAR, 1990.
S. A. Ringel, R. Sudharsanan, A. Rohatgi, M. S. Owens and H. P. Gillis. "Effects of Annealing and Surface Preparation on the Properties of Polycrystalline Cdznte Films Grown by Molecular-Beam Epitaxy," J. Vac. Sci. Technol. A-Vac. Surf. Films, vol. 8, pp. 2012-2019, MAY-JUN, 1990.

1989

S. A. Ringel, A. Rohatgi and S. P. Tobin. "An Approach Toward 25-Percent Efficient Gaas Heteroface Solar-Cells," IEEE Trans. Electron Devices, vol. 36, pp. 1230-1237, JUL, 1989.
A. Rohatgi, S. A. Ringel, R. Sudharsanan, P. V. Meyers, C. H. Liu and V. Ramanathan. "Investigation of Polycrystalline Cdznte, Cdmnte, and Cdte-Films for Photovoltaic Applications," Solar Cells, vol. 27, pp. 219-230, OCT-DEC, 1989.

1988

A. B. Dewald, R. L. Frost, S. A. Ringel, J. P. Schaffer, A. Rohatgi, B. Nielsen and K. G. Lynn. "Positron-Annihilation Spectroscopy of Algaas/gaas Interfaces in Metalorganic Chemical Vapor-Deposition Grown Gaas Heterojunction Solar-Cells," J. Vac. Sci. Technol. A-Vac. Surf. Films, vol. 6, pp. 2248-2252, JUL-AUG, 1988.
A. Rohatgi, S. A. Ringel, J. Welch, E. Meeks, K. Pollard, A. Erbil, C. J. Summers, P. V. Meyers and C. H. Liu. "Growth and Characterization of Cdmnte and Cdznte Polycrystalline Thin-Films for Solar-Cells," Solar Cells, vol. 24, pp. 185-194, MAY-JUN, 1988.

1987

S. A. Ringel and S. Ashok. "Silicon Surface-Barrier Modification by Low-Energy Nitrogen Ion-Implantation," J. Electrochem. Soc., vol. 134, pp. 1494-1499, JUN, 1987.

1986

S. Ashok and S. A. Ringel. "Low-Energy Hydrogen Implantation for Silicon Schottky-Barrier Modification," Vacuum, vol. 36, pp. 917-920, NOV-DEC, 1986.
K. Giewont, S. A. Ringel and S. Ashok. "Synergistic Effects in Ion-Bombardment Modification of Silicon Schottky Contacts," J. Vac. Sci. Technol. A-Vac. Surf. Films, vol. 4, pp. 845-846, MAY-JUN, 1986.
S. A. Ringel, H. C. Chien and S. Ashok. "Evidence for the Formation of Polycrystalline Silicon by Argon Implantation and its Passivation by Atomic-Hydrogen," Appl. Phys. Lett., vol. 49, pp. 728-730, SEP 22, 1986.
S. A. Ringel, X. C. Mu, S. J. Fonash and S. Ashok. "A Study of Target Heating in Low-Energy Ion-Beam Processing," J. Vac. Sci. Technol. A-Vac. Surf. Films, vol. 4, pp. 2385-2388, SEP-OCT, 1986.

2022

Hemant Ghadi, Joe F. McGlone, Zixuan Feng, AFM Anhar Uddin Bhuiyan, Yuxuan Zhang, Hongping Zhao, Aaron Arehart, Steve Ringel, Characterization of Deep Acceptors in β-Ga₂O₃ by Deep Level Optical Spectroscopy, GOX 2022, Washington DC, Invited 2022.
Hemant Ghadi, Joe F. McGlone, Zixuan Feng, Alexander Senckowski, Shivam Sharma, Man Hoi Wong and Uttam Singisetti, Aaron Arehart, Steven Ringel, Formation of Deep Acceptors by Nitrogen Implantation in HVPE Grown β-Ga2O3, Electronic Materials Conference 2022, Columbus Ohio.
A. V. Dheenan, N. K. Kalarickal, Z. Feng, A. Fiedler, C. Joishi, A. Price, D. Sushovan, J. F. McGlone, S. A. Ringel, H. Zhao, and S. Rajan, “β-Ga₂O₃ Lateral FinFETs Formed by Atomic Ga Flux Etching,” presented at the Gallium Oxide Workshop, Washington D.C., 2022.
J. F. McGlone, Z. Feng, N. K. Kalarickal, A. V. Dheenan, S. Rajan, H. Zhao, A. R. Arehart, and S. A. Ringel, “Low-dispersion MOCVD β-Ga₂O₃ δ-doped MESFET with a Mg-doped Buffer,” presented at the Device Reliability Conference (DRC), Columbus, OH, 2022.
N. K. Kalarickal, A. V. Dheenan, J. F. McGlone, A. Fiedler, S. Dhara, M. Brenner, S. A. Ringel, and S. Rajan, “Demonstration of β-Ga₂O₃ self-aligned delta doped MISFETs with current density > 550 mA/mm,” presented at the Electronic Materials Conference (EMC), Columbus, OH, 2022.
A. V. Dheenan, J. F. McGlone, N. K. Kalarickal, H.-L. Huang, M. Brenner, J. Hwang, S. A. Ringel, and S. Rajan, “β-Ga₂O₃ MESFETs with an Insulating Mg-doped Buffer Grown by MBE,” presented at the Electronic Materials Conference (EMC), Columbus, OH, 2022.
S. Dhara, N. K. Kalarickal, C. Joishi, A. Fiedler, J. F. McGlone, A. V. Dheenan, S. A. Ringel, and S. Rajan, “High Breakdown Field Strength in Molecular Beam Epitaxy-grown Al₂O₃/ β-Ga₂O₃ Structures,” presented at the Electronic Materials and Devices (EMC), Columbus, OH, 2022.
A. Bross Price, S. A. Ringel, T. J. Grassman, “Embedded HSQ Nanostructures in GaAs Homoepitaxy by MOCVD and MBE,” 65th International Conference on Electron, Ion and Photon Beam Technology and Nanofabrication, May 31 - June 3, 2022, New Orleans, LA, USA.
T. Kasher, H. Ghadi, J. T. Hart, Z. S. Bittner, A. Espenlaub, D. Derkacs, T. J. Grassman, S. A. Ringel, “Trap Analysis of C vs. Zn-doped 2.1eV AlGaInP irradiated by 3MeV Protons,” 27th Space Photovoltaic Research and Technology Conference, Aug. 2-4, 2022, Cleveland, OH, USA
Steven A. Ringel, Joe F. McGlone, H. Ghadi, A. Arehart, S. Rajan, and H. Zhou,” Perspectives on defects and reliability in UWBG semiconductors,” GOMAC, Feb. 2022, Miami. Invited
Steven A. Ringel, Hemant Ghadi, Joe F McGlone, Alexander Senckowski, Shivam Sharma, Man Hoi Wong and Uttam Singisetti, Investigation and Comparison of Deep Acceptors in β-Ga2O3 using Defect Spectroscopies,”6^th International Conference on Emerging Electronics, Bangalore, India Dec. 2022. Invited

2021

Hemant Ghadi, Joe F. McGlone, Zixuan Feng, A.F.M. Anhar Uddin Bhuiyan, Yuxuan Zhang, Hongping Zhao, Andrew Armstrong, George R. Burns, Gyorgy Vizkelethy, Ed Bielejec, Aaron R. Arehart, and Steven A. Ringel "Detailed investigation of MOCVD-grown β-Ga2O3 through quantitative defect spectroscopies", Proc. SPIE 11687, Oxide-based Materials and Devices XII, 116870T; https://doi.org/10.1117/12.2589947 (March 2021)
Lepkowski, Daniel L. and Kasher, Tal and Boyer, Jacob T. and Blumer, Zak H. and Yi, Chuqi and Juhl, Mattias K. and Soeriyadi, Anastasia H. and Mehrvarz, Hamid and Römer, Udo and Ho-Baillie, Anita and Bremner, Stephen P. and Ringel, Steven A. and Grassman, Tyler J., "Recent Advances in GaAsP/Si Top Cell Enabling 27% Tandem Efficiency," 2021 IEEE 48th Photovoltaic Specialists Conference (PVSC), pp. 1644-1646, doi: 10.1109/PVSC43889.2021.9518768 (June 2021)
J. T. Boyer, Z. H. Blumer, D. L. Lepkowski, S. A. Ringel and T. J. Grassman, "Exploring Multiple Pathways to Low TDD GaP/Si for III-V/Si Photovoltaics," 2021 IEEE 48th Photovoltaic Specialists Conference (PVSC), pp. 2144-2145, doi: 10.1109/PVSC43889.2021.9518431 (June 2021)
Wenbo Li, Yuxuan Zhang, Zhaoying Chen, Hongping Zhao, Steven A. Ringel, and Aaron R. Arehart, “Characterization of Traps in High-Growth-Rate MOCVD-Grown GaN,” 63^rd MRS Electronic Materials Conference (virtual), 2021. Peer-reviewed and extended abstract published.
Evan M. Cornuelle, Hemant Ghadi, Joe F. McGlone, A F M Anhar Uddin Bhuiyan, Zixuan Feng, Hongping Zhao, Aaron R. Arehart, and Steven A. Ringel, “Quantitative Defect Characterization of MOCVD-Grown β-(Al,Ga)2O3 and Comparison with β-Ga2O3,” 63rd MRS Electronic Materials Conference (virtual), 2021. Peer-reviewed and extended abstract published.
Yuxuan Zhang, Zhaoying Chen, Wenbo Li, Steven A. Ringel, Aaron R. Arehart, and Hongping Zhao, “MOCVD GaN epitaxy with fast growth rates,” 63rd MRS Electronic Materials Conference (virtual), 2021. Peer-reviewed and extended abstract published.
Ashok Dheenan, Zixuan Feng, Nidhin Kurian Kalarickal, Sushovan Dhara, Andreas Fiedle1,
Joe F. McGlone, Steven A. Ringel, Hongping Zhao, Siddharth Rajan, “High Current-Density β-Ga2O3 Lateral FinFETs,” Lester Eastman Conference, 2021. Abstract peer reviewed and published.
S.A. Ringel, “Ultra-Wide Bandgap β-Ga2O3: Status, Prospects and the Importance of Atomic Defects for Future Devices,” Spring meeting of the Materials Research Society, 2021. Abstract peer reviewed and published. INVITED

2020

S.A. Ringel, “Comparison of Traps in beta Ga2O3 Grown by MOCVD, MBE, LPCVD and EFG,” Workshop on Compound Semiconductor Materials and Devices (WOCSEMMAD), Palm Springs, CA (FEB 2020)
Jinwoo Hwang, Jared M. Johnson, Joel B. Varley, Aaron Arehart, Steven A. Ringel, and Chris G. Van de Walle "Atomic scale microscopy of point defects and their complexes in β-Ga2O3 (Conference Presentation)", Proc. SPIE 11281, Oxide-based Materials and Devices XI, 1128108 (March 2020) https://doi.org/10.1117/12.2552248
Steven Ringel, Aaron Arehart, Hemant Ghadi, Joseph McGlone, Esmat Farzana, James Speck, Akhil Mauze, Siddharth Rajan, Nidhin Kalarickal, Zhanbo Xia, “Defect Spectroscopy Of Ga2O3,” Bulletin of the American Physical Society 65 (2020). Invited.
D.L. Lepkowski, J.T. Boyer, C. Yi, A. Soeriyadi, Z.H. Blumer, H. Mehrvarz, D. Derkacs, C. Kerestes, A. Stavrides, S. Bremner, S.A. Ringel and T.J. Grassman, “Loss Analysis and Design Strategies Enabling > 23% GaAsP/Si Tandem Solar Cells,” 2020 IEEE 47th Photovoltaic Specialists Conference (PVSC), virtual location, 2020, DOI: 10.1109/PVSC45281.2020.9300787
V. LaSalvia, W. Nemeth, J.T. Boyer, D.L. Lepkowski, E.A. Makoutz, T.E. Saenz, S.A. Ringel, T.J. Grassman and E.L. Warren,“Improving GaAsP/Si Tandem Solar Cells Using Silicon Passivated Contacts,” 2020 IEEE 47th Photovoltaic Specialists Conference (PVSC), virtual location, 2020, DOI: 10.1109/PVSC45281.2020.9300356
J. T. Boyer, A. N. Blumer, Z. H. Blumer, F. A. Rodriguez, D. L. Lepkowski, S. A. Ringel, T. J. Grassman, “Development of Low-TDD GaAsyP1-y/GaP/Si Metamorphic Materials for High-Efficiency III-V/Si Photovoltaics,” 47th IEEE Photovoltaic Specialists Conference, 1680 (2020), DOI: 10.1109/PVSC45281.2020.9300803
Joe F. McGlone, Hemant Ghadi, Andrew Armstrong, George Burns, Zixuan Feng, A F M Anhar Uddin Bhuiyan, Hongping Zhao, Aaron R. Arehart and Steven A. Ringel, “Proton Radiation Effects on Electronic Defect States in High-Mobility MOCVD-Grown (010) β-Ga2O3,” MRS Electronic Materials Conference, virtual location (June 2020)
Hemant Ghadi, Joe F. McGlone, Rachel Adams, Zixuan Feng, A F M Anhar Uddin Bhuiyan, Hongping Zhao, Aaron R. Arehart and Steven A. Ringel, “Temperature Dependence of Electronic Defect States in High-Mobility MOCVD-Grown (010) β-Ga2O3,” MRS Electronic Materials Conference, virtual location (June 2020)
S. Li, R. Farshchi, M. Miller, A. R. Arehart and D. Kuciauskas, "Optical Characterization of Defects in High-efficiency (Ag,Cu)(In,Ga)Se2," 2020 47th IEEE Photovoltaic Specialists Conference (PVSC), Calgary, AB, Canada, 2020, pp. 2567-2569, doi: 10.1109/PVSC45281.2020.9300566.
Hemant Ghadi, Joe F. McGlone, Zixuan Feng, A.F.M. Anhar Uddin Bhuiyan, Yuxuan Zhang, Hongping Zhao, Andrew Armstrong, George R. Burns, Gyorgy Vizkelethy, Ed Bielejec, Aaron R. Arehart, Steven A. Ringel, "Detailed investigation of MOCVD-grown β-Ga2O3 through quantitative defect spectroscopies," Proc. SPIE 11687, Oxide-based Materials and Devices XII, 116870T (5 March 2021); doi.org/10.1117/12.2589947
D. L. Lepkowski, T. Kasher, T. J. Grassman, S. A. Ringel, “Theoretical Evaluation of DBR Structures for Improving Tolerance to Threading Dislocations in GaAsP/Si Tandem Solar Cells,”62nd Electronic Materials Conference, June 2020 (virtual)
T. Kasher, Z. H. Blumer, J. T. Boyer, D. L. Lepkowski, T. J. Grassman, and S. A. Ringel, “Exploration of RF Sputtered Ga2O3 as a Transparent Conductive Oxide for Application to photovoltaics,” 62nd Electronic Materials Conference, June 2020 (virtual)
Yuxuan Zhang, Zhaoying Chen, Wenbo Li, Md Rezaul Karim, Aaron Arehart, Steven A. Ringel and Hongping Zhao, “Probing Deep Acceptors in MOCVD GaN-on-GaN—Toward High Power GaN Vertical Devices,” Materials Research Society (MRS), 2020 (virtual)
Hemant Ghadi, Joe F. McGlone, Zixuan Feng, Yuxuan Zhang, Hongping Zhao, Aaron R. Arehart and Steven A. Ringel, “ Deep level defects in LPCVD-grown β-Ga2O3 (010),” Materials Research Society (MRS), 2020 (virtual)
Joe F. McGlone, Nidhin K. Kalarickal, Zhanbo Xia, Siddharth Rajan, Aaron Arehart, and Steven Ringel, “Radiation Impact on Si δ-Doped β-Ga2O3 MESFETs,” Materials Research Society (MRS), 2020 (virtual)
Nidhin Kurian Kalarickal, Zixuan Feng, Zhanbo Xia, Anhar Uddin, Wyatt Moore, Joe F. McGlone, Hongping Zhao, Aaron R. Arehart, Steven A. Ringel, Siddharth Rajan, “BaTiO3/β-Ga2O3 MESFET with power figure of merit of 376 MW/cm2,” in Electronic Materials Conference, 2020 (virtual)
Zixuan Feng, A F M Anhar Uddin Bhuiyan, Zhanbo Xia, Joe F. McGlone, David R. Daughton, Aaron R. Arehart, Steven A. Ringel, Siddharth Rajan, and Hongping Zhao, “Probing charge transport and background doping in MOCVD grown (010) β-Ga2O3,” in Electronic Materials Conference, 2020 (virtual)
Towhidur Razzak, Hao Xue, Hareesh Chandrasekar, Mohammad K. Hussain, Shahadat H. Sohel, Mohammad Wahidur Rahman, Sanyam Bajaj, Joe F. McGlone, Steven A. Ringel, Asif Khan, Wu Lu, and Siddharth Rajan, “Low-Field Transport in High Al-Composition AlxGa1-xN Channel High Electron Mobility Transistors,” in Electronic Materials Conference, 2020 (virtual)
Siming Li, R. Farshchi, M. Miller, Aaron R. Arehart, D. Kuciauskas, “Optical characterization of defects in high-efficiency (Ag, Cu)(In, Ga)Se2,” Photovoltaics Specialists Conference 47, Banff, Canada, 2020
Michael F. Miller, Siming Li, Pran K. Paul, Darius Kuciauskas, Rouin Farshchi and Aaron Arehart, “Impact of K-Optimization on Trap Concentrations in ACIGS Solar Cells,” 62nd Electronic Materials Conference, Columbus, OH, 2020 (virtual)

2019

S.A. Ringel, D.L. Lepkowski, J.T. Boyer and T.J. Grassman, “High-Efficiency, Defect-Tolerant and High-Reliability III-V/Si Tandem Solar Cells,” XXth Workshop on the Physics of Semiconductor Devices (IWPSD-XX), Calcutta, India (DEC 2019). Invited.
S.A. Ringel, “Trap spectroscopy of beta-Ga2O3 Materials and Transistors,” Indo-US Workshop on “Frontiers of Excellence in Wide and Ultrawide Bandgap Semiconductors and Electronic Systems,” Mumbai, India (DEC 2019). Invited.
Hemant Ghadi, Christine M. Jackson, Esmat Farzana, Joe F. McGlone, Zixuan Feng, A.F.M Anhar Uddin Bhuiyan, Hongping Zhao, Aaron R. Arehart and Steven A. Ringel, “Full-Bandgap Investigation of Electronic Defect States in High-Mobility MOCVD-Grown (010) β-Ga2O3,” 3rd International Workshop on Gallium Oxide (MRS), Columbus, OH (AUG 2019)
Daniel Lepkowski, Tal Kasher, Jacob T. Boyer, Dan J. Chmielewski, Tyler J. Grassman and Steven A. Ringel, “The Critical Role of Window Design in Rear-Emitter Solar Cells,” 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC), Chicago, IL, USA, 2019, pp. 1021-1024 (JUNE 2019) Best Student Poster Award
Jacob T. Boyer, Daniel L. Lepkowski, Daniel Derkacs, Christopher Kerestes, Alex Stavrides, Steven Whipple, Steven A. Ringel and Tyler J. Grassman, “Development and Characterization of III-V/Si Multijunction Photovoltaics for Space Application,” 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC), Chicago, IL, USA, 2019, pp. 2822-2825 (JUNE 2019)
Tyler J. Grassman, Daniel L. Lepkowski, Jacob T. Boyer, Daniel J. Chmielewski, Chuqi Yi, Ned Western, Hamid Mehrvarz, Anita Ho-Baillie, Christopher Kerestes, Daniel Derkacs, Steven G. Whipple, Alex P. Stavrides, Stephen P. Bremner and Steven A. Ringel, “Toward >25% Efficient Monolithic Epitaxial GaAsP/Si Tandem Solar Cells,” 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC), Chicago, IL, USA, 2019, pp. 0734-0737 (JUNE 2019)
Daniel L. Lepkowski, Jacob T. Boyer, Daniel J. Chmielewski, Tyler J. Grassman, Steven A. Ringel,, Chuqi Yi, Ned Western, Hamid Mehrvarz, Anita Ho-Baillie, Stephen P. Bremner, Christopher Kerestes, Daniel Derkacs, Steven G. Whipple and Alex P. Stavrides,“Progress toward >30% Efficient III-V/Si Tandem Photovoltaics,” MRS Electronic Materials Conference, Ann Arbor, MI (JUNE 2019)
A. Arehart, E. Farzana, J. McGlone, C.M. Jackson, S.A. Ringel, “Beta Gallium Oxide Traps: Materials to Devices,” Proc. Electrochemical Society Meeting, Austin TX (MAY 2019) Invited
S.A. Ringel, “Electronic Defects in Gallium Oxide Materials and Devices,” Workshop on Compound Semiconductor Materials and Devices (WOCSEMMAD), Jacksonville, FL (FEB 2019) Invited
S.A. Ringel and A.R. Arehart, “Defects in gallium oxide and their trapping effects in devices,” 3rd UltraWide Bandgap (UWBG) Workshop, Adelphi, MD (MAY 2019) Invited
S.A. Ringel, E. Farzana, J. McGlone, C. Jackson, H. Ghadi, Z. Xia, S. Rajan, T. Blue, A. Mauze, J.S. Speck and A.R. Arehart, “Deep Level Defects and Trapping Effects in Gallium Oxide Materials and Transistors,” SPIE Photonics West, San Francisco, CA (FEB 2019) Invited

2018

Steven Ringel, Esmat Farzana, Joe McGlone, Christine Jackson, Hemant Ghadi, Zhanbo Xia, Siddharth Rajan, Thomas Blue, Akhil Mauze, James S. Speck and Aaron Arehart, “Traps Due to Native Defects and Impurities in Gallium Oxide,” IEEE EDS 4th ICEE (International Conference on Emerging Electronics), Bangalore, India (2018). Invited.
Esmat Farzana, Akhil Mauze, James S. Speck, Aaron R. Arehart, and Steven A. Ringel, “Impact of Neutron Irradiation on Deep Levels in Ge-Doped (010) β-Ga2O3 Layers Grown by Plasma-Assisted Molecular Beam Epitaxy,” Fall Materials Research Society Meeting Boston, MA (2018)
Steven A. Ringel, “Epitaxial Pathways for III-V/Si Photovoltaics,” North American Molecular Beam Epitaxy Conference (24th AVS NAMBE), Banff, Canada (2018). Invited.
Steven A. Ringel, Aaron Arehart, Esmat Farzana, Joe McGlone, Christine Jackson, Zhanbo Xia, Chandan Joishi, Max Chaiken, Tom Blue, Siddharth Rajan, “Gallium oxide electronic Defect Characterization,” 3rd Domestic Gallium Oxide Workshop, Columbus, OH (2018). Invited.
Esmat Farzana, Tom Blue, Aaron R. Arehart and Steven A. Ringel, “Investigation of Neutron Irradiation on Deep Levels in beta-Ga2O3,” LEC2018 (Les Eastman Conference), Columbus, OH (2018.
Daniel L. Lepkowski ; Jacob T. Boyer ; Daniel J. Chmielewski ; Amber C. Silvaggio ; Steven A. Ringel ; Tyler J. Grassman, “Investigation of Rear-Emitter GaAsP Top Cells for use in III-V/Si Tandem Photovoltaics,” Proc. IEEE 45th Photovoltaic Specialists Conf., Waikoloa, HI, pp. 2642-2647 (2018), DOI: 10.1109/PVSC.2018.8547748
Chuqi Yi, Fa-Jun Ma, Hamid Mehrvarz, Daniel Lepkowski, Jacob Boyer, Daniel Chmielewski, John A. Carlin, Steven A. Ringel, Tyler J. Grassman, Anita Ho-Baillie and Stephen Bremner, “Effect of Silicon Front Surface Doping Profile on GaP/Si Heterostructure for III-V/GaP/Si Multi-junction Solar Cells,” Proc. IEEE 45th Photovoltaic Specialists Conf., Waikoloa, HI, pp. 275-278 (2018), DOI: 10.1109/PVSC.2018.8547600
Daniel J. Chmielewski, Daniel L. Lepkowski, Jacob T. Boyer, John A. Carlin, Tyler J. Grassman and Steven A. Ringel, “High Performance Metamorphic Tunnel Junctions for GaAsP/Si Tandem Solar Cells Grown via MOCVD,” Proc. IEEE 45th Photovoltaic Specialists Conf., Waikoloa, HI, pp. 2631-2634 (2018); DOI: 10.1109/PVSC.2018.8547444
Joe McGlone, Chandan Joishi, Zhanbo Xia, Siddharth Rajan, Steven Ringel and Aaron Arehart, “Trapping Effects in Si δ-Doped β-Ga2O3 MESFETs,” Compound Semiconductor Week (CSW), Boston, MA (2018).
S.A. Ringel, T.J. Grassman, D. Lepkowski, J. Boyer and D. Chmielewski, “Recent Advances in III-V/Si Tandem Solar Cells,” Electronic Materials and Nanostructures (EMN) Conf., Singapore (2018). Invited.
Steven Ringel, Esmat Farzana, Joe McGlone, Zhanbo Xia, Yuewei Zhang, Chandan Joishi, Elaheh Ahmadi, Akhil Mauze, Thomas Blue, Siddharth Rajan, James S. Speck and Aaron Arehart, “The Presence and Impact of Deep Level Defects Induced by High Energy Neutron Radiation in Beta-Phase Gallium Oxide,” Proc. 43rd GOMACTEC-2018, Miami, FL, March 12-15, 2018. Invited.
S.A. Ringel “Electronic Defects in Gallium Oxide Materials and Devices,” Workshop on Compound Semiconductor Materials and Devices (WOCSEMMAD), San Diego, CA, Feb. 18-21, 2018. Invited

2017

W. Sun, Z. Zhang, T. Mohsin, E. Farzana, B. McSkimming, C. Lee, P. Saunier, J. Speck, S. A. Ringel, and A. R. Arehart, “General model for irradiation-induced degradation of GaN HEMTs”, ROCS, Indian Wells, CA, May 22 - May 25, 2017.
W. Sun, S. A. Ringel, and A. R. Arehart, “Ec-0.90 eV trap-induced threshold voltage instability in GaN/Si MISHEMTs”, CS MANTECH, Indian Wells, CA, May 22 - May 25, 2017.
Ringel, Tyler J. Grassman, “Development of an Optimized GaAsP Cell for Implementation in a III- V/Si Tandem Structure”, 44th IEEE Photovoltaic Specialist Conference, Washington, DC June 25- 30, 2017.
Daniel J. Chmielewski, Christine Jackson, Jacob Boyer, Daniel Lepkowski, John A. Carlin, Aaron R. Arehart, Tyler J. Grassman, and Steven A. Ringel, “Comparative Study of >2 eV Lattice-Matched and Metamorphic (Al)GaInP Materials and Solar Cells Grown by MOCVD”, 44th IEEE Photovoltaic Specialist Conference, Washington, DC, June 25-30, 2017.
Jacob T. Boyer, Daniel L. Lepkowski, Daniel J. Chmielewski, Steven A. Ringel, Tyler J. Grassman, “Graded (AlzGa1-z)xIn1-xP Window-Emitter Structures for Improved Short-Wavelength Response”, PVSC-44, IEEE Photovoltaic Specialists Conference, Washington DC, June 25-30, 2017.

A.R. Arehart, E. Farzana, and S.A. Ringel, “Impact of Neutron Irradiation on Electronic Defects in B-Ga2O3,” 2nd International Workshop on Gallium Oxide and Related Materials, Parma, Italy, September 12-15, 2017.

K. Galiano, J. I. Deitz, S. D. Carnevale, D. A. Gleason, P. K. Paul, Z. Zhang, B. McSkimming, J. S. Speck, S. A. Ringel, T. J. Grassman, A. R. Arehart, J. P. Pelz, “Investigating Local Variations in the Activation Energy of EC-0.57 eV Traps in GaN”, 17th Conference on Defects-Recognition, Imaging and Physics in Semiconductors (DRIP XVII), Valladolid Spain, October 8-12, 2017.

2016

D. J. Chmielewski, K. Galiano, P. Paul, D. Cardwell, S. Carnevale, J. A. Carlin, A. R. Arehart, T. J. Grassman, and S. A. Ringel, “Comparative Study of 2.05 eV AlGaInP and Metamorphic GaInP Materials and Solar Cells Grown by MBE and MOCVD” presented at IEEE International Reliability Physics Symposium, Pasadena CA, April 17-24, 2016.
W. Sun, C. Lee, P. Saunier, S. A. Ringel, and A. R. Arehart, “Investigation of trapping effects on AlGaN/GaN HEMT under DC accelerated life testing” presented at IEEE International Reliability Physics Symposium, Pasadena CA, April 17-24, 2016.
T. Razzak, C.M. Jackson, S.Sohel, F. Akyol, S. Bajaj, S. Rajan, A.R. Arehart, S.A. Ringel, "Investigation of Deep Levels in High-Al Mole Fraction Al 0.75Ga0.25N" presented at IWN, International Workshop on Nitride Semiconductors, Orlando FL, 2-7 October, 2016.
K. Galiano, J. Deitz, S. Carnevale, D. A. Gleason, Z. Zhang, B. McSkimming, J. S. Speck, S. A. Ringel, T. J. Grassman, A. R. Arehart, and J. P. Pelz, "Spatially Correlating the EC-0.57 eV Trap in GaN with Edge Dislocations", presented at IWN, International Workshop on Nitride Semiconductors, Orlando FL, 2-7 October, 2016.
A.R. Arehart, W. Sun, K. Galiano, S.Sohel, J.I. Deitz, S.A. Ringel, J.P. Pelz , and T.J. Grassman, "Toward an Understanding of Defects and Device Reliability in GaN Hemts" presented at ECS Prime, Honolulu HI 2-7 October 2016.
D.J. Chmielewski, K. Galiano, Pran Paul, D. Cardwell, S. Carnevale, J.A. Carlin, A.R. Arehart, T.J. Grassman, and S.A. Ringel, "Comparative Study of 2.05 eV AlGaInP and Metamorphic GaInP Materials and Solar Cells Grown by MBE and MOCVD", presented at SPRAT the 24th Space Photovoltaic Research and Technology Conference, Cleveland OH 20-22 September 2016.
E. Farzana, Z. Zeng, S. Kaun, J. S. Speck, A. R. Arehart and S. A. Ringel, "Characterization of Deep Level Defects in beta-Ga2O3", presented at MRS 58 th Electronic Materials Conference, Delaware NE, 22-24 June 2016.
P. K. Paul, K. Aryal, S. Marsillac, S. A. Ringel, and A. R. Arehart,, “Impact of the Ga/In ratio on defects in Cu(In,Ga)Se2,” 43rd IEEE Photovoltaic Specialists Conference, Portland, OR, June 5-10, 2016.
P. K. Paul, K. Aryal, S. Marsillac, S. A. Ringel, and A. R. Arehart, “Identifying the source of reduced performance in 1-stage-grown Cu(In,Ga)Se2 solar cells,” 43rd IEEE Photovoltaic Specialists Conference, Portland, OR, June 5-10, 2016.
D.J. Chmielewski, K. Galiano, P. Paul, D. Cardwell, S. Carnevale, J.A. Carlin, A.R. Arehart, T.J. Grassman, and S.A. Ringel, “Comparative Study of 2.05 eV AlGaInP and Metamorphic GaInP Materials and Solar Cells Grown by MBE and MOCVD,” 43rd IEEE Photovoltaic Specialists Conference, Portland, OR, June 5-10, 2016.
J. I. Deitz, D. W. McComb, and T. J. Grassman, “Probing the electronic structure at the heterovalent GaP/Si interface using electron energy-loss spectroscopy,” in 2016 IEEE 43rd Photovoltaic Specialists Conference (PVSC), 1545–1548, 5-10 June 2016
T. J. Grassman, D. J. Chmielewski, J. A. Carlin, and S. A. Ringel, “Development of epitaxial 2- and 3-junction III-V/Si solar cells,” in 2016 IEEE 43rd Photovoltaic Specialists Conference (PVSC), 2036–2039, 5-10 June 2016

2015

A. Sasikumar, Z. Zhang, P. Kumar, E. X. Zhang, D. M. Fleetwood, R. D. Schrimpf, P. Saunier, C. Lee, S. A. Ringel, A. R. Arehar “Proton irradiation-induced traps causing VT instabilities and RF degradation in GaN HEMTs”, in IEEE Intl. Reliab. Phys. Symp., 2015.
A. R. Arehart, A. Sasikumar, Z. Zhang, P. Kumar, B. Poling, G. D. Via, E. Heller, D. M. Fleetwood, R. D. Schrimpf, P. Saunier, C. Lee, and Steven A. Ringel, “Comparison of Irradiation and Electrical Stressors on AlGaN/GaN HEMT Reliability”, in Govt. Microcircuit Appl. Critical Tech. Conf. (GOMACTech), 2015.

2014

J. Deitz, S. Carnevale, M. De Graef, Y. N. Picard, S. A. Ringel, T. J. Grassman, D. W. McComb, "Using Electron Channeling Contrast Imaging for Misfit Dislocation Characterization in Heteroepitaxial III-V/Si Thin Films," Microscopy and Microanalysis 20(S3), 2014, pp. 552-553.
S. D. Carnevale, J. I. Deitz, J. A. Carlin, Y. N. Picard, M. De Graef, S. A. Ringel, T. J. Grassman, “Rapid Characterization of Extended Defects in III-V/Si by Electron Channeling Contrast Imaging,” Proc. 40th IEEE Photovoltaic Specialists Conference, 2014, pp. 2800.
J. S. Speck, Z. Zhang, A. R. Arehart, E. Cinkilic, J. Chen, E. X. Zhang, Y. S. Puzyrev, C. X. Zhang, M. W. McCurdy, S. T. Pantelides, B. McSkimming, S. W. Kaun, E. C. H. Kyle, D. M. Fleetwood, R. D. Schrimpf, S. A. Ringel, “Proton Irradiation in Bulk GaN Layers and Nitride-based HEMT Devices,” in Govt. Microcircuit Appl. Critical Tech. Conf. (GOMACTech) 2014.
C. Ratcliff, T. J. Grassman, J. A. Carlin, D. J. Chmielewski and S. A. Ringel, "Ga-rich GaxIn1-xP solar cells on si with 1.95 eV bandgap for ideal III-V/Si photovoltaics," in Proceedings of SPIE, 2014, pp. 898118.
A. Sasikumar, A. R. Arehart, S. W. Kaun, J. Chen, E. X. Zhang, D. M. Fleetwood, R. D. Schrimpf, J. S. Speck and S. A. Ringel, "Defects in GaN based transistors," in Proceedings of SPIE, 2014, pp. 89861C.
A. Sasikumar, D. W. Cardwell, A. R. Arehart, J. Lu, S. W. Kaun, S. Keller, U. K. Mishra, J. S. Speck, J. P. Pelz and S. A. Ringel, "Toward a physical understanding of the reliability-limiting E-C-0.57 eV trap in GaN HEMTs," in International Reliability Physics Symposium, 2014.

2013

I. Al Mansouri, S. Bremner, A. Ho-Baillie, H. Mehrvarz, X. Hao, G. Conibeer, M. A. Green, T. J. Grassman, J. A. Carlin and S. A. Ringel, "Design of bottom silicon solar cell for multijunction devices," in 39th IEEE Photovoltaic Specialists Conference (PVSC), 2013, pp. 3310-3314.
D. J. Chmielewski, T. J. Grassman, A. M. Carlin, J. Carlin, A. Speelman and S. A. Ringel, "Metamorphic tunnel junctions for high efficiency III-V/IV multi-junction solar cell technology," in IEEE Photovoltaic Specialists Conference, 2013, pp. 882-885.
T. J. Grassman, J. A. Carlin, C. Ratcliff, D. J. Chmielewski and S. A. Ringel, "Epitaxially-grown metamorphic GaAsP/Si dual-junction solar cells," in IEEE Photovoltaic Specialists Conference, 2013, pp. 149-153.
T. J. Grassman, D. B. Shah, J. A. Carlin and S. A. Ringel, "Exploration of epitaxial quantum dots within wide band gap metamorphic host materials for intermediate band solar cells," in IEEE Photovoltaic Specialists Conference, 2013, pp. 284-287.
S. A. Ringel, J. A. Carlin, T. J. Grassman, B. Galiana, A. M. Carlin, C. Ratcliff, D. Chmielewski, L. Yang, M. J. Mills, A. Mansouri, S. P. Bremner, A. Ho-Baillie, X. Hao, H. Mehrvarz, G. Conibeer and M. A. Green, "Ideal GaP/Si heterostructures grown by MOCVD: III-V/Active-si subcells, multijuntions, and MBE-to-MOCVD III-V/Si interface science," in IEEE Photovoltaic Specialists Conference, 2013, pp. 3383-3388.

2012

A. M. Carlin, T. J. Grassman, M. R. Brenner, J. Grandal, C. Ratcliff, L. Yang, M. Mills, P. Sharma, E. A. Fitzgerald and S. A. Ringel, "Lattice-matched GaP/SiGe virtual substrates for low-dislocation density GaInP/GaAsP/Si solar cells," in 2012, pp. 918-921.
J. Grandal, T. J. Grassman, A. M. Carlin, M. R. Brenner, B. Galiana, J. A. Carlin, L. Yang, M. J. Mills and S. A. Ringel, "Growth and characterization of InGaAs quantum dots on metamorphic GaAsP templates by molecular beam epitaxy," in 38th IEEE Photovoltaic Specialists Conference (PVSC), 2012, pp. 1783-1787.
T. J. Grassman, C. Ratcliff, A. M. Carlin, J. A. Carlin, L. -. Yang, M. J. Mills and S. A. Ringel, "III-V/GaP epitaxy on si for advanced photovoltaics and green light emitters," in ECS Transactions, 2012, pp. 321-332.
T. J. Grassman, A. M. Carlin, J. Grandal, C. Ratcliff, L. Yang, M. J. Mills and S. A. Ringel, "Spectrum-optimized si-based III-V multijunction photovoltaics," in Proceedings of SPIE, 2012, pp. 82560R.
A. Sasikumar, A. Arehart, S. A. Ringel, S. Kaun, M. H. Wong, U. K. Mishra and J. S. Speck, "Direct correlation between specific trap formation and electric stress-induced degradation in MBE-grown AlGaN/GaN HEMTs," in IEEE International Reliability Physics Symposium (IRPS), 2012, .
K. Swaminathan, T. J. Grassman, L. -. Yang, D. Chmielewski, M. Mills and S. A. Ringel, "Impact of threading dislocation density on metamorphic InxGa1-xAs and InzGa1-zP p-i-n photodetectors on GaAs," in Proceedings of SPIE, 2012, pp. 82571A.

2010

A. R. Arehart, M. R. Brenner, Z. Zhang, K. Swaminathan and S. A. Ringel, "Traps in algainp materials and devices lattice matched to gaas for multi-junction solar cells," in IEEE Photovoltaic Specialists Conference, 2010, pp. 1999-2001.
A. R. Arehart, A. Sasikumar, G. D. Via, B. Winningham, B. Poling, E. Heller and S. A. Ringel, "Spatially-discriminating trap characterization methods for HEMTs and their application to RF-stressed AlGaN/GaN HEMTs," in International Electron Devices Meeting, 2010, .
T. J. Grassman, A. M. Carlin and S. A. Ringel, "Metamorphic gaasp and ingap photovoltaic materials on si for high-efficiency iii-V/si multijunction solar cells," in IEEE Photovoltaic Specialists Conference, 2010, pp. 2029-2033.
J. H. Warner, S. I. Maximenk, S. R. Messenger, R. J. Walters, S. A. Ringel, M. R. Brenner and A. M. Carlin, "Electrical characterization of electron and proton-induced defects in P+n gaas photodiodes: Ebic study," in IEEE Photovoltaic Specialists Conference, 2010, pp. 002646.

2009

X. J. Chen, H. J. Barnaby, J. H. Warner, S. R. Messenger, R. J. Walters, S. A. Ringel and J. Park, "Non-linear behaviors of dark current slope in p(+)n gaas solar cells following proton irradiations," in IEEE Photovoltaic Specialists Conference, 2009, pp. 1532-1537.
T. J. Grassman, M. R. Brenner, A. M. Carlin, S. Rajagopalan, R. Unocic, R. Dehoff, M. Mills, H. Fraser and S. A. Ringel, "Toward metamorphic multijunction GaAsP/Si photovoltaics grown on optimized GaP/Si virtual substrates using anion-graded GaAs(y)P(1-y) buffers," in IEEE Photovoltaic Specialists Conference, 2009, pp. 2011-2016.
T. K. Ng, S. F. Yoon, K. H. Tan, W. K. Loke, S. Wicaksono, K. L. Lew, K. P. Chen, E. A. Fitzgerald, A. J. Pitera, S. A. Ringel, A. M. Carlin and M. Gonzalez, "1ev gan(x)as(1-x-y)sb(y) material for lattice-matched iii-v solar cell implementation on gaas and ge," in IEEE Photovoltaic Specialists Conference, 2009, pp. 1130-1134.

2008

D. M. Wilt, A. T. Pal, S. A. Ringel, E. A. Fitzgerald, P. P. Jenkins and R. Walters, "FINAL RESULTS FROM THE MISSE5 GaAs ON si SOLAR CELL EXPERIMENT," in IEEE Photovoltaic Specialists Conference, 2008, pp. 2078-2081.

2007

A. Armstrong, A. Chakraborty, J. S. Speck, S. P. DenBaars, U. K. Mishra and S. A. Ringel, "Characterization and discrimination of AlGaN- and GaN-related deep levels in AlGaN/GaN heterostructures," in Aip Conference Proceedings, 2007, pp. 223-224.
D. Liu, M. Hudait, Y. Lin, S. A. Ringel and W. Lu, "80nm In0.52Al0.48As/In0.53Ga0.47As/InAs0.3P0.7 composite channel HEMT with an f(T) of 280GHz," in International Semiconductor Device Research Symposium, College Pk, MD, 2007, pp. 549.

2006

K. Lee, B. VanMil, M. Luo, T. H. Myers, A. Armstrong, S. A. Ringel, M. Rummukainen and K. Saarinen, "Compensation in be-doped gallium nitride grown using molecular beam epitaxy," in Materials Research Society Symposium Proceedings, 2006, pp. 729-734.
D. M. Wilt, S. A. Ringel, E. A. Fitzgerald and P. P. Jenkins, "Preliminary on-orbit performance data from GaAs on si solar cells aboard misses," in 4th World Conference on Photovoltaic Energy Conversion, Waikoloa, HI, 2006, pp. 1918.

2005

A. Armstrong, D. Green, A. Arehart, U. Mishra, J. Speck and S. Ringel, "Carbon-related deep states in compensated n-type and semi-insulating GaN : C and their influence on yellow luminescence," in Materials Research Society Symposium Proceedings, 2005, pp. 311-316.
D. Liu, M. Hudait, Y. Lin, H. Kim, S. A. Ringel and W. Lu, "0.25 mu m in(0.52)A1(0.48)As/In(0.53)ga(0.47)As/InAs(0.3)P(0.7) composite channel HEMTs with an f(T) of 115GHz," in Asia Pacific Microwave Conference-Proceedings, Suzhou, China, 2005, pp. 829.
M. Lueck, M. Gonzalez, O. Kwon, C. Andre and S. Ringel, "Impact of annealing and V : III ratio on properties of MBE grown wide-bandgap AIGaInP materials and solar cells," in Ieee Photovoltaic Specialists Conference, 2005, pp. 711-714.
S. Ringel, C. Andre, E. Fitzgerald, A. Pitera and D. Wilt, "Multi-junction III-V photovoltaics on lattice-engineered si sustrates," in Ieee Photovoltaic Specialists Conference, 2005, pp. 567-570.
S. Ringel, C. Andre, M. Lueck, D. Isaacson, A. Pitera, E. Fitzgerald and D. Wilt, "III-V multi-junction materials and solar cells on engineered SiGe/Si substrates," in Materials Research Society Symposium Proceedings, 2005, pp. 211-222.
C. Tivarus, K. Park, M. Hudait, S. Ringel and J. Pelz, "Nanoscale characterization of metal/semiconductor nanocontacts," in Aip Conference Proceedings, 2005, pp. 280-284.
D. Wilt, A. Pal, N. Prokop, S. Ringel, C. Andre, M. Smith, D. Scheiman, P. Jenkins, W. Maurer, B. McElroy and E. Fitzgerald, "Thermal cycle testing of GaAs on si and metamorphic tandem on si solar cells," in Ieee Photovoltaic Specialists Conference, 2005, pp. 571-574.

2004

A. Armstrong, A. Arehart, B. Moran, S. DenBaars, U. Mishra, J. Speck and S. Ringel, "Impact of growth pressure on defects in GaN grown by metalorganic chemical vapor deposition," in 30th International Symposium on Compound Semiconductors, San Diego, CA, 2004, pp. 48.
O. Kwon, J. Boeckl, M. Lee, A. Pitera, E. Fitzgerald and S. Ringel, "Growth and properties of AlGaInP resonant cavity light emitting diodes (RCLEDs) on Ge/SiGe/Si substrates," in Materials Research Society Symposium Proceedings, 2004, pp. 161-166.

2003

A. Arehart, C. Poblenz, B. Heying, J. Speck, U. Mishra, S. DenBaars and S. Ringel, "Influence of growth parameters on the deep level spectrum in MBE-grown n-GaN," in Materials Research Society Symposium Proceedings, 2003, pp. 735-740.
A. Armstrong, A. Arehart, S. Ringel, B. Moran, S. DenBaars, U. Mishra and J. Speck, "Identification of carbon-related bandgap states in GaN grown by MOCVD," in Materials Research Society Symposium Proceedings, 2003, pp. 509-514.
S. Ringel, C. Andre, M. Hudait, D. Wilt, E. Clark, A. Pitera, M. Lee, E. Fitzgerald, M. Carroll, M. Erdtmann, E. Carlin and B. Keyes, "Toward high performance N/P GaAs solar cells grown on low dislocation density p-type sige substrates," in 3rd World Conference on Photovoltaic Energy Conversion, Osaka, Japan, 2003, pp. 615.

2002

C. Andre, A. Khan, M. Gonzalez, M. Hudait, E. Fitzgerald, J. Carlin, M. Currie, C. Leitz, T. Langdo, E. Clark, D. Wilt and S. Ringel, "Impact of threading dislocations on both n/p and p/n single junction GaAs cells grown on Ge/SiGe/Si substrates," in 29th IEEE Photovoltaic Specialists Conference, NEW ORLEANS, LA, 2002, pp. 1046.
M. Hudait, Y. Lin, C. Andre, P. Sinha, C. Tivarus, J. Pelz, D. Wilt and S. Ringel, "Relaxed InAsP layers grown on step graded InAsP buffers by solid source MBE," in Materials Research Society Symposium Proceedings, 2002, pp. 287-292.
R. Kaplar, S. Ringel, S. Kurtz, A. Allerman and J. Klem, "Comparison of deep level spectra of MBE- and MOCVD-grown InGaAsN," in Materials Research Society Symposium Proceedings, 2002, pp. 403-408.

2000

J. Carlin, M. Hudait, S. Ringel, D. Wilt, E. Clark, C. Leitz, M. Currie, T. Langdo and E. Fitzgerald, "High efficiency GaAs-on-si solar cells with high V-oc using graded GeSi buffers," in Ieee Photovoltaic Specialists Conference, 2000, pp. 1006-1011.
A. Hierro, J. Boeckl, S. Ringel, M. Hansen, U. Mishra, S. DenBaars, J. Speck and D. Look, "Detection and identification of deep levels in n-GaN," in International Workshop on Nitride Semiconductors (IWN 2000), Nagoya, Japan, 2000, pp. 462.

1999

M. Clevenger, C. Murray, S. Ringel, R. Sacks, L. Qin, G. Charache and D. Depoy, "Optical properties of thin semiconductor device structures with reflective back-surface layers," in Aip Conference Proceedings, 1999, pp. 327-334.
A. Hierro, D. Kwon, S. Ringel, L. Brillson, A. Young and A. Franciosi, "Deep level characterization of interface-engineered ZnSe layers grown by molecular beam epitaxy on GaAs," in Materials Research Society Symposium Proceedings, 1999, pp. 77-82.
D. Kwon, R. Kaplar, J. Boeckl, S. Ringel, A. Allerman, S. Kurtz and E. Jones, "Keep level defect studies in MOCVD-grown InxGa1-xAs1-yNy films lattice-matched to GaAs," in Materials Research Society Symposium Proceedings, 1999, pp. 59-64.
S. Ringel, J. Carlin, R. Sieg, J. Boeckl and E. Fitzgerald, "Highly-controlled GaAs/Ge interfaces and implications for III-V optoelectronic integration onto group IV substrates," in 1st International Workshop on Lattice-Mismatched and Heterovalent Thin Film Epitaxy, Castelvecchio Pas, Italy, 1999, pp. 96.
S. Ringel, R. Sacks, L. Qin, M. Clevenger and C. Murray, "Growth and properties of InGaAs/FeAl/InAlAs/InP heterostructures for buried reflector/interconnect applications in InGaAs thermophotovoltaic devices," in Aip Conference Proceedings, 1999, pp. 142-151.

1998

R. Hoffman, N. Fatemi, V. Weizer, P. Jenkins, M. Stan, S. Ringel, R. Sieg, D. Scheiman, D. Wilt and D. Brinker, "The effect of the zn interstitial defect on the performance of p/n InP solar cells," in Materials Research Society Symposium Proceedings, 1998, pp. 235-240.

1997

B. Chatterjee, S. Ringel and R. Hoffman, "Hydrogen-interstitial zn defect complexes and their effects on the device characteristics of heteroepitaxial p(+)n InP cell structures," in Ieee Photovoltaic Specialists Conference, 1997, pp. 907-910.
R. Hoffman, N. Fatemi, P. Jenkins, V. Weizer, M. Stan, S. Ringel, D. Scheiman, D. Wilt, D. Brinker, R. Walters and S. Messenger, "Improved performance of p/n InP solar cells," in Ieee Photovoltaic Specialists Conference, 1997, pp. 815-818.
S. Ringel and P. Grillot, "Dislocation interactions and their impact on electrical properties of GeSi-based heterostructures," in Materials Research Society Symposium Proceedings, 1997, pp. 313-324.
S. Ringel, R. Sieg, S. Ting and E. Fitzgerald, "Anti-phase domain-free GaAs on ge substrates grown by molecular beam epitaxy for space solar cell applications," in Ieee Photovoltaic Specialists Conference, 1997, pp. 793-798.

1996

B. Chatterjee, S. Ringel and R. Hoffman, "A comparison of hydrogen passivation in heteroepitaxial n(+)p and p(+)n solar cells," in 25th IEEE Photovoltaic Specialists Conference, Washington, DC, 1996, pp. 182.
R. Hoffman, N. Fatemi, P. Jenkins, D. Scheiman, S. Ringel, W. Davis, V. Weizer, D. Wilt and D. Brinker, "Development of high efficiency p(+)/n InP solar cells for hetero-epitaxial applications," in 25th IEEE Photovoltaic Specialists Conference, Washington, DC, 1996, pp. 174.

1994

B. Chatterjee, S. A. Ringel, R. Sieg, I. Weinberg and R. Hoffman, "Deep-level characterization and passivation in heteroepitaxial InP," in Materials Research Society Symposium Proceedings, Boston, MA, 1994, pp. 125-130.
P. N. Grillot, S. A. Ringel, G. P. Watson, E. A. Fitzgerald and Y. H. Xie, "Electronic characterization of dislocations in rtcvd germanium-silicon silicon grown by graded layer epitaxy," in Materials Research Society Symposium Proceedings, 1994, pp. 159-164.
S. A. Ringel, B. Chatterjee, R. M. Sieg and E. V. Schnetzer, "Material quality and dislocation trapping in hydrogen passivated heteroepitaxial InP/GaAs and InP/Ge solar cells," in Ieee Photovoltaic Specialists Conference, 1994, pp. 2204-2207.

1991

A. ROHATGI, S. RINGEL, R. SUDHARSANAN and H. CHOU, "An improved understanding of efficiency limiting defects in polycrystalline Cdte/cds solar-cells," in Ieee Photovoltaic Specialists Conference, LAS VEGAS, NV, 1991, pp. 966.

1988

S. A. Ringel and A. Rohatgi, "Material quality and design optimization for high-efficiency gaas solar-cells," in Ieee Photovoltaic Specialists Conference, LAS VEGAS, NV, 1988, pp. 671.
A. ROHATGI, R. SUDHARSANAN, S. RINGEL, P. MEYERS and C. LIU, "Wide bandgap thin-film solar-cells from cdte alloys," in Ieee Photovoltaic Specialists Conference, LAS VEGAS, NV, 1988, pp. 1481.

Institute for Materials Research (IMR)

https://imr.osu.edu/

Semiconductor Epitaxy and Analysis Lab – SEAL https://seal.osu.edu/

Contact: Mark Brenner brenner.34@osu.edu

095 Dreese Lab, 2015 Neil Avenue, Columbus, OH 43210

The Semiconductor Epitaxy and Analysis Laboratory (SEAL) is OSU’s primary facility for molecular beam epitaxy (MBE) and is located within the 4,000 square foot Dreese Lab Cleanroom (DLC) and is a core facility that is co-managed by the Ohio State Institute for Materials Research (IMR; imr.osu.edu). SEAL houses six state of the art MBE chambers, each dedicated to different material systems, to ensure high quality material epitaxy for both basic studies and true device development. SEAL can provide epitaxial growth of crystalline layers, heterostructures, quantum and nanostructures, and devices ranging from solar cells and infrared photodetectors, to high electron mobility transistors, 2D structures and power devices.

SEAL started out life as part of Professor Ringel’s EMDL group, when he founded the EMDL MBE (molecular beam epitaxy) lab in 1994, housing the first MBE system in the State of Ohio outside of AFRL. This initial investment was made through OSU’s former Center for Materials Research (CMR) and the Office of the Vice President for Research. As SEAL grew from this single MBE system in 1000 sqft of space within the ECE Dreese Lab Cleanroom, to 6 MBEs in 2500 sqft, Professor Ringel formally established SEAL as a staffed user facility open to all in 2000. Over time, Professor Ringel incorporated select characterization facilities that support MBE growth into SEAL’s user facility structure. Over time, and with additional faculty joining the ECE department, the MSE department and the Institute for Materials Research (imr.osu.edu), including Professors Grassman, Krishna, Myers and Rajan, SEAL is now a world-class MBE facility.

Currently SEAL houses 6 molecular beam epitaxy (MBE) systems: system 1 for III-AsP materials; system 2 for Si-Ge-Sn materials; system 3 is a plasma-assisted MBE chamber for growth of GaN and related materials; system 4 is a PAMBE tool dedicated to Ga2O3 and related materials; system 5 is dedicated to 2D transition metal and group-III chalcogenides; and system 6 is

dedicated to III-Sb materials and related compounds. SEAL also houses an array of materials characterization and processing capabilities that support epitaxial growth, including high resolution triple axis XRD, Hall Effect transport measurements (including variable field and temperature analyses), photoluminescence spectroscopy, etc. SEAL is a staffed user based cost center within the college of engineering and the ECE department. SEAL is also a member of the IMR network of laboratories at OSU which coordinates research activities and infrastructure related to the science and engineering of materials throughout OSU.

Defect Spectroscopy Laboratories

Contact: Aaron Arehart arehart.5@osu.edu

360 Caldwell Lab, 2024 Neil Ave., Columbus OH 43210

This unique, specialized group of laboratories housed in OSU’s Department of Electrical and Computer Engineering is dedicated to the characterization of electrically active deep level defects in semiconductors and is one of the largest such clusters in the world, with 9 total defect spectroscopy measurement systems. The labs, which were established starting in 1991 as EMDL’s first research capability with a single deep level transient spectroscopy (DLTS) system, include complete, state-of-the-art facilities to conduct a variety of capacitance and current-based trap spectroscopies applicable to semiconductor materials, heterostructures and devices. The combination of conventional thermal-emission based DLTS and photocapacitance-based deep level optical spectroscopy (DLOS) facilitates trap characterization abilities for materials having bandgaps up to ~5.5 eV. The additional use of constant capacitance mode and constant current mode DLTS and DLOS allows for trap characterization within a variety of structures, from bulk materials to heterostructures and transistor architectures. Up to 1000V can be applied with our high-voltage DLTS and DLOS system, revealing deep level response during real high voltage transistor operating conditions. Our nano-DLTS systems are capable of detecting localized trap at high lateral spatial resolution, enabling site-specific connections between trap responses and microstructure, throughout the bandgap. The combined facilities allow for characterization of traps from very narrow bandgap (e.g. InAs) to ultrawide bandgap (e.g. AlN and Ga2O3) semiconductors, in applications that include photovoltaics, power electronics, and infrared-visible-ultraviolet photonics. To date we have significant experience in defect spectroscopy studies on materials and devices that include GaN, AlGaN and other III-Nitrides, GaAs, GaInP, InP, InAs and other III-V compounds including III-V/Si heteroepitaxial structures, SiGe, SiC, Ga2O3, CuInGaSe and other advanced semiconductors. Our probe stations are configurable to perform measurements on a variety of device structures, such as high electron mobility transistors, light emitting diodes, solar cells, photo-detectors, and metal-insulator-semiconductor capacitors, and fully packaged power electronics.

Major Capabilities include:

Variable temperature probe stations
DC and pulsed I-V and I-V-T
C-V, C-T, C-f, and lighted C-V
capacitance and current-based DLTS
capacitance and current-based DLOS
scanning “nano” DLTS/DLOS

Admittance Spectroscopy

Internal Photoemission
Scanning Kelvin Probe and Atomic Force Microscopy (SKPM, AFM)
Thermally Stimulated Current/Capacitance

ECE Microelectronics Cleanroom

https://dlc.engineering.osu.edu/
Contact: Mark Brenner brenner.34@osu.edu
095 Dreese Lab, 2015 Neil Avenue, Columbus, OH 43210

Processing Cleanrooms for Microfabrication includes 4000 square feet of class 100 and 1000 areas with additional associated laboratory space. There are facilities to process and fabricate silicon integrated circuits and III-V devices, and this capability has been demonstrated by the implementation of circuits in a variety of technologies (MOS, bipolar, FETs, optoelectronics, and photovoltaics). The processing equipment include a Technics Planar Etch II Plasma Reactor for dielectric deposition, hydrogen processing, and etching; CHA 4-Pocket electron beam evaporator; NRC filament evaporator; ellipsometer; DekTak profilomiter; Karl Suss MJB-3 mask aligner; Kasper and Cobilt aligners and associated photolithography equipment; annealing, oxidation and diffusion furnaces; a pulsed laser deposition facility; West Bond wire bonder; Kenworth probe station with Hewlett-Packard 4145; 4-point probe; wet chemical clean benches, etc. In addition to EE faculty, staff and students, the facilities are available to researchers from Physics, Material Science, Chemical Engineering, Chemistry, Mechanical Engineering, Welding Engineering and from outside Ohio State University.

Center for Electron Microscopy and Analysis – CEMAS

https://cemas.osu.edu/

The Center for Electron Microscopy and Analysis (CEMAS) is a centralized, coordinated imaging facility where traditional boundaries between disciplines are eliminated.

With one of the largest concentrations of electron and ion beam analytical microscopy instruments in any North American institution, CEMAS brings together multidisciplinary expertise to drive synergy, amplify characterization capabilities, and challenge what is possible in analytical electron microscopy.

Our world-class multidisciplinary approach enables academic and business partners to "see more" than ever before.

Our full-service facility - from extensive sample preparation laboratories to image-processing tools and support - allows researchers to carry out their entire microscopy and analysis program at CEMAS. Located in a custom designed facility on The Ohio State University's West Campus, every instrument in the facility meets or exceeds manufacturer performance specifications.

Nanotech West Laboratory - NTWest

https://nanotech.osu.edu/

The Nanotech West Lab of Ohio State is the largest nanotechnology user facility in the state of Ohio. Serving both internal (Ohio State) and external users, Nanotech West supports more than 100 research and development projects per year including use many external users, predominantly startup companies in the Ohio region. Nanotech West consists of a 6,000 square foot class 100 cleanroom facility, a 4,000 square foot Biohybrid Laboratory, and other laboratory and office space.

Nanotech West is staffed by 7 full-time engineers, 2 part-time support engineers, 1 full-time administrator, and additional Associate Staff and engineering and office student interns. Most of the engineering Core Staff have extensive experience in semiconductor or closely related industries.

NanoSystems Laboratory – NSL

http://ensl.osu.edu/

The NanoSystems Laboratory's goal is to provide academic and industrial users with access to advanced material characterization and fabrication tools for research and development applications. NSL is located on the Columbus Campus of The Ohio State University in the Physics Research Building.

Research capabilities available at NSL include focused ion beam/scanning electron microscopy, e-beam lithography, nanomanipulation, EDS X-ray microanalysis, X-ray diffractometry, SQUID magnetometry, atomic force/magnetic force microscopy, low temperature magnetotransport measurements and Langmuir-Blodgett trough monolayer deposition.

Electronic Materials and Devices Laboratory

Electronic Materials & Devices Laboratory

WELCOME to the Electronic Materials & Devices Lab

If you have an update for this page please contact Jennifer Donovan donovan.205@osu.edu

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