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Steven Ringel

  • Assoc VP & IMR Executive Dir, OR - Inst for Material Res
  • Professor, Physics
  • Professor, Materials Science Engineering
  • Professor, Neal A Smith Chair, Electrical & Computer Engr.
  • Room #375
    2024 Neil Ave
    Columbus, OH 43210
  • 614-292-6904

About

Bio

Steven A. Ringel is the Neal Smith Endowed Chair Professor in the Department of Electrical and Computer Engineering at The Ohio State University.  He is also the founding and current Executive Director of The Ohio State University Institute for Materials Research (IMR), and he is the Faculty Director of Ohio State’s Materials and Manufacturing for Sustainability (M&MS) Discovery Theme.  IMR is Ohio State’s largest non-medical research center, with more than 200 faculty members from 22 academic departments in 5 colleges, performing more than $75M in annual research on a base of awards valued at more than $400M.  Within the IMR umbrella are state-of-the-art core facility centers, national centers of excellence and industry-university consortia.  The M&MS Discovery Theme is a paradigm-shifting effort at Ohio State to create pre-eminence in materials and technologies for sustainability, focusing on innovation and industry deployment.  

Professor Ringel is internationally recognized for his seminal contributions and leadership in the field of electronic materials and devices, particularly in photovoltaics, defect characterization techniques, wide bandgap semiconductors, and compound semiconductor-silicon integration. Specific to photovoltaics (PV), Dr. Ringel has spent much of his career making high impact contributions; his early work on CdTe solar cells revealed basic mechanisms behind the now standard cadmium chloride treatment applied in this global technology, his efforts in space PV resulted in the highest performance InP space solar cells at the time, and his group is world-recognized for its advancement of PV based on III-V/SiGe materials.  More recently, his group has produced the first large area, III-V/active-Si tandem and triple junction cells, translating these high-performance, low-cost technologies to industry. Dr. Ringel’s general focus on materials defects, their characterization and growth mitigation strategies have similarly made lasting impact on wide bandgap device technologies, including the invention of deep level optical spectroscopy methods that have been adopted by industry to solve GaN reliability issues. As co-founder and editor of the IEEE J-PV, the General Chair of the 2015 42nd IEEE PVSC and the former Chair of the international IEEE Photovoltaics Technical Committee, Dr Ringel has helped to define future directions in PV research and education.  

Professor Ringel has authored and co-authored more than 300 technical articles and conference presentations, given more than 120 invited talks, and has authored or edited 4 books and numerous chapters. At OSU he has produced more than 70 PhD and MS students. His recognitions include the 1994 NSF National Young Investigator Award, the Ohio State Distinguished Scholar Award, the Ohio State Scott Award for Outstanding Academic Achievement in Engineering, the OSU Harrison Award for Excellence in Engineering, seven best paper awards from international conferences and societies, AAAS Fellow and AIAA Associate Fellow. He sits on several international boards (Tyndall Institute in Ireland, Singapore-MIT Alliance for Research and Technology (SMART) - for which he is chair of the LEES IRG board, and the Sandia National Labs UWBG center), he has been a visiting professor numerous times (UPM-Spain, NTU-Singapore, Cardiff),  and he is a co-founder of several startup companies. Dr. Ringel received his Ph.D. degree in Electrical Engineering from Georgia Tech in 1991, and his M.S. and B.S. degrees from Penn State in 1986 and 1984, respectively. 

Education

Ph.D. 1991, Georgia Institute of Technology

Research Interests

Electronic materials and devices, photovoltaics, defect engineering, epitaxy and innovation in defect characterization methods; Broad interests in the science and application of electronic materials for applications in energy, electronics and optoelectronic technologies; Defect engineering in semiconductors and development of methods for trap spectroscopy; with applications to wide bandgap semiconductor devices and new materials; Substrate engineering; heterogeneous integration and interface science; The academic-industry research interface; Translational materials and its role in global innovation in solar energy, next generation electronics and general technology development.

Office

375 Caldwell Laboratory

Personal website

https://emdl.osu.edu/

Honors

  • 2015

    Advisor, Best Student Paper Award: Zeng Zhang. .

  • 2015

    Distinguished Scholar Award. .

  • 2014

    Honorary Professor. .

  • 2014

    Chair, Scientific Advisory Board/Visiting Committee. .

  • 2014

    Member, Advisory Board. .

  • 2013

    Invited Tutorial Speaker. .

  • 2012

    Clara M. and Peter L. Scott Award for Outstanding Achievement. .

  • 2010

    Lumley Research Award. .

  • 2004-2009

    Invited Guest Lecturer. .

  • 2008

    Visiting Professor. .

  • 2008

    Co-investigator of Clean Energy Research Program. .

  • 2008

    Visiting Professor. .

  • 2008

    Associate Fellow. .

  • 2007

    Invited Tutorial Speaker. .

  • 2005

    AAAS Fellow. .

  • 2005

    Lumley Research Award. .

  • 2004

    Advisor, MRS Gold Medal Student Award: A. Armstrong. .

  • 2004

    Neal A. Smith Endowed Chair. .

  • 2003

    Advisor, Best Student Paper Award: O. Kwon. .

  • 2001

    Advisor, Best Student Paper Award: R. Kaplar. .

  • 2000

    Lumley Research Award. .

  • 2000

    Advisor, MRS Gold Medal Student Award: A. Hierro. .

  • 1999

    Stanley F. Harrison Faculty Award for Excellence in Engineering Research & Education. .

  • 1999

    Stanley E. Harrison Faculty Award for Excellence in Engineering. .

  • 1994

    National Young Investigator Award.

Edited Books

2002

  • Schwarz, R.B., Ceder, G., Ringel, S.A.. 2002. "Materials for Energy Storage, Generation and Transport." Warrendale: Materials Research Society Press.

1999

  • S.A. Ringel, S.A., Fitzgerald, E.A., Adesida, I., Houghton, D.. 1999. "III-V and IV-IV Materials and Processing Challenges for Highly Integrated Microelectronics and Optoelectronics." Warrendale: Materials Research Society Press.

1995

  • Buckley, D.N., Ringel, S.A., Ren, F.. 1995. "Symposium on Large Area Wafer Growth and Processing for Electronic and Photonic Devices and the Twentieth State of the Art Program on Compound Semiconductors." Pennington: The Electrochemical Society Press.

Chapters

2013

  • Ringel, S.A., Anderson, T.J., Green, M., Singh, R., Walters, R.J.. 2013. "Photovoltaic Devices." edited by Burghharz, Joachim N, 213 - 224. New York City: Wiley-IEEE Press.

2010

  • Ringel, SA, Grassman TJ. 2010. "The III-V solar cell on Silicon." edited by Li, T., E. Piner, E., Dadgar, A., Boca Raton: CRC Press.

1998

  • Ringel,SA, Grillot, PN. 1998. "Electronic Properties and Deep Levels in Germanium-Silicon." edited by Bean, J., Hull, R., 293 - 346. Cambridge: Academic Press.

1997

  • S.A.Ringel, SA, Chatterjee, B. 1997. "Hydrogenation of Compound Semiconductors." edited by Pearton, SJ, 243 - 263. Ontario: Research Signpost Publications.

Journal Articles

2016

  • Xuan Sang Nguyen,X,S; Goh,Xuan,Long; Zhang,Li; Zhang,Zeng; Arehart,Aaron,R; Ringel,Steven,A; Fitzgerald,Eugene,A; Chua,Soo,Jin, 2016, "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, no. 6, 060306 -
  • Liu,X; Jackson,C,M; Wu,F; Mazumder,B; Yeluri,R; Kim,J; Keller,S; Arehart,A,R; Ringel,S,A; Speck,J,S; Mishra,U,K, 2016, "Electrical and structural characterizations of crystallized AI(2)O(3)/GaN interfaces formed by in situ metalorganic chemical vapor deposition." JOURNAL OF APPLIED PHYSICS 119, no. 1, 015303 -
  • Zhang,Z; Cardwell,D; Sasikumar,A; Kyle,E,CH; Chen,J; Zhang,E,X; Fleetwood,D,M; Schrimpf,R,D; Speck,J,S; Arehart,A,R; Ringel,S,A, 2016, "Correlation of proton irradiation induced threshold voltage shifts to deep level traps in AlGaN/GaN heterostructures." JOURNAL OF APPLIED PHYSICS 119, no. 16, 165704 -
  • Garcia-Tabares,Elisa; Carlin,John,A; Grassman,Tyler,J; Martin,Diego; Rey-Stolle,Ignacio; Ringel,Steven,A, 2016, "Evolution of silicon bulk lifetime during III-V-on-Si multijunction solar cell epitaxial growth." PROGRESS IN PHOTOVOLTAICS 24, no. 5, 634 - 644.
  • Grassman,Tyler,J; Chmielewski,Daniel,J; Carnevale,Santino,D; Carlin,John,A; Ringel,Steven,A, 2016, "GaAs0.75 P-0.25/Si Dual-Junction Solar Cells Grown by MBE and MOCVD." IEEE JOURNAL OF PHOTOVOLTAICS 6, no. 1, 326 - 331.
  • Zhang,Z; Farzana,E; Arehart,A,R; Ringel,S,A, 2016, "Deep level defects throughout the bandgap of (010) beta-Ga2O3 detected by optically and thermally stimulated defect spectroscopy." APPLIED PHYSICS LETTERS 108, no. 5, 052105 -
  • Arehart,A,R; Sasikumar,A; Via,G,D; Poling,B; Heller,E,R; Ringel,S,A, 2016, "Evidence for causality between GaN RF HEMT degradation and the E-C-0.57 eV trap in GaN." MICROELECTRONICS RELIABILITY 56, 45 - 48.
  • Sasikumar,A; Arehart,A,R; Cardwell,D,W; Jackson,C,M; Sun,W; Zhang,Z; Ringel,S,A, 2016, "Deep trap-induced dynamic on-resistance degradation in GaN-on-Si power MISHEMTs." MICROELECTRONICS RELIABILITY 56, 37 - 44.

2015

  • Chen,Jin; Puzyrev,Yevgeniy,S; Jiang,Rong; Zhang,En,Xia; McCurdy,Michael,W; Fleetwood,Daniel,M; Schrimpf,Ronald,D; Pantelides,Sokrates,T; Arehart,Aaron,R; Ringel,Steven,A; Saunier,Paul; Lee,Cathy, 2015, "Effects of Applied Bias and High Field Stress on the Radiation Response of GaN/AlGaN HEMTs." IEEE TRANSACTIONS ON NUCLEAR SCIENCE 62, no. 6, 2423 - 2430.
  • Carnevale,Santino,D; Deitz,Julia,I; Carlin,John,A; Picard,Yoosuf,N; McComb,David,W; De Graef,Marc; Ringel,Steven,A; Grassman,Tyler,J, 2015, "Applications of Electron Channeling Contrast Imaging for the Rapid Characterization of Extended Defects in III-V/Si Heterostructures." IEEE JOURNAL OF PHOTOVOLTAICS 5, no. 2, 676 - 682.
  • Zhang,Z; Arehart,A,R; Kyle,E,CH; Chen,J; Zhang,E,X; Fleetwood,D,M; Schrimpf,R,D; Speck,J,S; Ringel,S,A, 2015, "Proton irradiation effects on deep level states in Mg-doped p-type GaN grown by ammonia-based molecular beam epitaxy." APPLIED PHYSICS LETTERS 106, no. 2, 022104 -
  • Almansouri,Ibraheem; Bremner,Stephen; Ho-Baillie,Anita; Mehrvarz,Hamid; Hao,Xiaojing; Conibeer,Gavin; Grassman,Tyler,J; Carlin,John,A; Haas,Alexander; Ringel,Steven,A; Green,Martin,A, 2015, "Designing Bottom Silicon Solar Cells for Multijunction Devices." IEEE JOURNAL OF PHOTOVOLTAICS 5, no. 2, 683 - 690.
  • Deitz,Julia,I; Carnevale,Santino,D; Ringel,Steven,A; McComb,David,W; Grassman,Tyler,J, 2015, "Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization." JOVE-JOURNAL OF VISUALIZED EXPERIMENTS NA, no. 101, e52745 -
  • Paul,P,K; Cardwell,D,W; Jackson,C,M; Galiano,K; Aryal,K; Pelz,J,P; Marsillac,S; Ringel,S,A; Grassman,T,J; Arehart,A,R, 2015, "Direct nm-Scale Spatial Mapping of Traps in CIGS." IEEE JOURNAL OF PHOTOVOLTAICS 5, no. 5, 1482 - 1486.
  • Zhang,Z; Farzana,E; Sun,W,Y; Chen,J; Zhang,E,X; Fleetwood,D,M; Schrimpf,R,D; McSkimming,B; Kyle,E,CH; Speck,J,S; Arehart,A,R; Ringel,S,A, 2015, "Thermal stability of deep level defects induced by high energy proton irradiation in n-type GaN." JOURNAL OF APPLIED PHYSICS 118, no. 15, 155701 -
  • Sasikumar,A; Arehart,A,R; Via,G,D; Winningham,B; Poling,B; Heller,E; Ringel,S,A, 2015, "Identification of an RF degradation mechanism in GaN based HEMTs triggered by midgap traps." MICROELECTRONICS RELIABILITY 55, no. 11, 2258 - 2262.

2014

  • Carnevale,Santino,D; Deitz,Julia,I; Carlin,John,A; Picard,Yoosuf,N; De Graef,Marc; Ringel,Steven,A; Grassman,Tyler,J, 2014, "Rapid misfit dislocation characterization in heteroepitaxial III-V/Si thin films by electron channeling contrast imaging." APPLIED PHYSICS LETTERS 104, no. 23, 232111 -
  • Zhang,Zeng; Jackson,Christine,M; Arehart,Aaron,R; McSkimming,Brian; Speck,James,S; Ringel,Steven,A, 2014, "Direct Determination of Energy Band Alignments of Ni/Al2O3/GaN MOS Structures Using Internal Photoemission Spectroscopy." JOURNAL OF ELECTRONIC MATERIALS 43, no. 4, 828 - 832.
  • Grassman,T,J; Carlin,J,A; Galiana,B; Yang,F; Mills,M,J; Ringel,S,A, 2014, "MOCVD-Grown GaP/Si Subcells for Integrated III-V/Si Multijunction Photovoltaics." IEEE JOURNAL OF PHOTOVOLTAICS 4, no. 3, 972 - 980.
  • Chmielewski,Daniel,J; Grassman,Tyler,J; Carlin,Andrew,M; Carlin,John,A; Speelman,Austin,J; Ringel,Steven,A, 2014, "Metamorphic GaAsP Tunnel Junctions for High-Efficiency III-V/IV Multijunction Solar Cell Technology." IEEE JOURNAL OF PHOTOVOLTAICS 4, no. 5, 1301 - 1305.

2013

  • Long,R,D; Jackson,C,M; Yang,J; Hazeghi,A; Hitzman,C; Majety,S; Arehart,A,R; Nishi,Y; Ma,T,P; Ringel,S,A; McIntyre,P,C, 2013, "Interface trap evaluation of Pd/Al2O3/GaN metal oxide semiconductor capacitors and the influence of near-interface hydrogen." APPLIED PHYSICS LETTERS 103, no. 20, 201607 -
  • Arehart,A,R; Sasikumar,A; Rajan,S; Via,G,D; Poling,B; Winningham,B; Heller,E,R; Brown,D; Pei,Y; RECHT,F; Mishra,U,K; Ringel,S,A, 2013, "Direct observation of 0.57 eV trap-related RF output power reduction in AlGaN/GaN high electron mobility transistors." SOLID-STATE ELECTRONICS 80, 19 - 22.
  • Long,R,D; Jackson,C,M; Yang,J; Hazeghi,A; Hitzman,C; Majety,S; Arehart,A,R; Nishi,Y; Ma,T,P; Ringel,S,A; McIntyre,P,C, 2013, "Interface trap evaluation of Pd/Al2O3/GaN metal oxide semiconductor capacitors and the influence of near-interface hydrogen." APPLIED PHYSICS LETTERS 103, no. 20, 201607 -
  • Jackson,Christine,M; Arehart,Aaron,R; Cinkilic,Emre; McSkimming,Brian; Speck,James,S; Ringel,Steven,A, 2013, "Interface trap characterization of atomic layer deposition Al2O3/GaN metal-insulator-semiconductor capacitors using optically and thermally based deep level spectroscopies." JOURNAL OF APPLIED PHYSICS 113, no. 20, 204505 -
  • Grassman,T,J; Carlin,J,A; Galiana,B; Yang,L-M; Yang,F; Mills,M,J; Ringel,S,A, 2013, "Nucleation-related defect-free GaP/Si(100) heteroepitaxy via metal-organic chemical vapor deposition." APPLIED PHYSICS LETTERS 102, no. 14, 142102 -
  • Zhang,Z; Arehart,A,R; Cinkilic,E; Chen,J; Zhang,E,X; Fleetwood,D,M; Schrimpf,R,D; McSkimming,B; Speck,J,S; Ringel,S,A, 2013, "Impact of proton irradiation on deep level states in n-GaN." APPLIED PHYSICS LETTERS 103, no. 4, 042102 -
  • Cardwell,D,W; Sasikumar,A; Arehart,A,R; Kaun,S,W; Lu,J; Keller,S; Speck,J,S; Mishra,U,K; Ringel,S,A; Pelz,J,P, 2013, "Spatially-resolved spectroscopic measurements of E-c-0.57 eV traps in AlGaN/GaN high electron mobility transistors." APPLIED PHYSICS LETTERS 102, no. 19, 193509 -
  • Sasikumar,A; Arehart,A,R; Martin-Horcajo,S; Romero,M,F; Pei,Y; Brown,D; RECHT,F; di Forte-Poisson,M,A; Calle,F; Tadjer,M,J; Keller,S; DenBaars,S,P; Mishra,U,K; Ringel,S,A, 2013, "Direct comparison of traps in InAlN/GaN and AlGaN/GaN high electron mobility transistors using constant drain current deep level transient spectroscopy." APPLIED PHYSICS LETTERS 103, no. 3, 033509 -

2012

  • Sasikumar,A; Arehart,A; Kolluri,S; Wong,M,H; Keller,S; DenBaars,S,P; Speck,J,S; Mishra,U,K; Ringel,S,A, 2012, "Access-Region Defect Spectroscopy of DC-Stressed N-Polar GaN MIS-HEMTs." IEEE ELECTRON DEVICE LETTERS 33, no. 5, 658 - 660.
  • Cardwell,D,W; Arehart,A,R; Poblenz,C; Pei,Y; Speck,J,S; Mishra,U,K; Ringel,S,A; Pelz,J,P, 2012, "Nm-scale measurements of fast surface potential transients in an AlGaN/GaN high electron mobility transistor." APPLIED PHYSICS LETTERS 100, no. 19, 193507 -
  • Zhang,Z; Hurni,C,A; Arehart,A,R; Yang,J; Myers,R,C; Speck,J,S; Ringel,S,A, 2012, "Deep traps in nonpolar m-plane GaN grown by ammonia-based molecular beam epitaxy." APPLIED PHYSICS LETTERS 100, no. 5, 052114 -
  • Gur,Emre; Tabares,G; Arehart,A; Chauveau,J,M; Hierro,A; Ringel,S,A, 2012, "Deep levels in a-plane, high Mg-content MgxZn1-xO epitaxial layers grown by molecular beam epitaxy." JOURNAL OF APPLIED PHYSICS 112, no. 12, 123709 -
  • Zhang,Z; Hurni,C,A; Arehart,A,R; Speck,J,S; Ringel,S,A, 2012, "Influence of V/III growth flux ratio on trap states in m-plane GaN grown by ammonia-based molecular beam epitaxy." APPLIED PHYSICS LETTERS 101, no. 15, 152104 -

2011

  • Tan,K,H; Wicaksono,S; Loke,W,K; Li,D; Yoon,S,F; Fitzgerald,E,A; Ringel,S,A; Harris,J,S, 2011, "Molecular beam epitaxy grown GaNAsSb 1 eV photovoltaic cell." JOURNAL OF CRYSTAL GROWTH 335, no. 1, 66 - 69.
  • Swaminathan,K; Grassman,T,J; Yang,L-M; Gu,Q; Mills,M,J; Ringel,S,A, 2011, "Optically-aligned visible/near-infrared dual-band photodetector materials and devices on GaAs using metamorphic epitaxy." JOURNAL OF APPLIED PHYSICS 110, no. 6, 063109 -
  • Swaminathan,K; Yang,L-M; Grassman,T,J; Tabares,G; Guzman,A; Hierro,A; Mills,M,J; Ringel,S,A, 2011, "Metamorphic In0.20Ga0.80As p-i-n photodetectors grown on GaAs substrates for near infrared applications." OPTICS EXPRESS 19, no. 8, 7280 - 7288.
  • Nath,Digbijoy,N; Guer,Emre; Ringel,Steven,A; Rajan,Siddharth, 2011, "Growth model for plasma-assisted molecular beam epitaxy of N-polar and Ga-polar InxGa1-xN." JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 29, no. 2, 021206 -
  • Gonzalez,M; Carlin,A,M; Dohrman,C,L; Fitzgerald,E,A; Ringel,S,A, 2011, "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." JOURNAL OF APPLIED PHYSICS 109, no. 6, 063709 -
  • Arehart,A,R; Allerman,A,A; Ringel,S,A, 2011, "Electrical characterization of n-type Al0.30Ga0.70N Schottky diodes." JOURNAL OF APPLIED PHYSICS 109, no. 11, 114506 -
  • Gur,Emre; Zhang,Zeng; Krishnamoorty,Sriram; Rajan,S; Ringel,S,A, 2011, "Detailed characterization of deep level defects in InGaN Schottky diodes by optical and thermal deep level spectroscopies." APPLIED PHYSICS LETTERS 99, no. 9, 092109 -
  • RATCLIFF,C; Grassman,T,J; Carlin,J,A; Ringel,S,A, 2011, "High temperature step-flow growth of gallium phosphide by molecular beam epitaxy and metalorganic chemical vapor deposition." APPLIED PHYSICS LETTERS 99, no. 14, 141905 -

2010

  • Yang,Chieh,Kai; Roblin,Patrick; De Groote,Fabien; Ringel,Steven,A; Rajan,Siddharth; Teyssier,Jean,Pierre; Poblenz,Christiane; Pei,Yi; Speck,James; Mishra,Umesh,K, 2010, "Pulsed-IV Pulsed-RF Cold-FET Parasitic Extraction of Biased AlGaN/GaN HEMTs Using Large Signal Network Analyzer." IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES 58, no. 5, 1077 - 1088.
  • Warner,Jeffrey,H; Cress,Cory,D; Messenger,Scott,R; Walters,Robert,J; Ringel,Steve,A; Park,Jeongho, 2010, "A Deep Level Transient Spectroscopy Study of Electron and Proton Irradiated p(+) n GaAs Diodes." IEEE TRANSACTIONS ON NUCLEAR SCIENCE 57, no. 4, 1940 - 1945.
  • Nath,Digbijoy,N; Gur,Emre; Ringel,Steven,A; Rajan,Siddharth, 2010, "Molecular beam epitaxy of N-polar InGaN." APPLIED PHYSICS LETTERS 97, no. 7, 071903 -
  • Grassman,Tyler,J; Brenner,Mark,R; Gonzalez,Maria; Carlin,Andrew,M; Unocic,Raymond,R; Dehoff,Ryan,R; Mills,Michael,J; Ringel,Steven,A, 2010, "Characterization of Metamorphic GaAsP/Si Materials and Devices for Photovoltaic Applications." IEEE TRANSACTIONS ON ELECTRON DEVICES 57, no. 12, 3361 - 3369.
  • Arehart,A,R; Poblenz,C; Speck,J,S; Ringel,S,A, 2010, "Effect of nitrogen plasma power on defect levels in Ni/n-GaN Schottky diodes grown by molecular beam epitaxy." JOURNAL OF APPLIED PHYSICS 107, no. 5, 054518 -
  • Arehart,A,R; Homan,T; Wong,M,H; Poblenz,C; Speck,J,S; Ringel,S,A, 2010, "Impact of N- and Ga-face polarity on the incorporation of deep levels in n-type GaN grown by molecular beam epitaxy." APPLIED PHYSICS LETTERS 96, no. 24, 242112 -

2009

  • Hudait,Mantu,K; Brenner,M; Ringel,S,A, 2009, "Metamorphic In0.7Al0.3As/In0.69Ga0.31As thermophotovoltaic devices grown on graded InAsyP1-y buffers by molecular beam epitaxy." SOLID-STATE ELECTRONICS 53, no. 1, 102 - 106.
  • Grassman,T,J; Brenner,M,R; Rajagopalan,S; Unocic,R; DEHOFF,R; Mills,M; Fraser,H; Ringel,S,A, 2009, "Control and elimination of nucleation-related defects in GaP/Si(001) heteroepitaxy." APPLIED PHYSICS LETTERS 94, no. 23, 232106 -
  • Hudait,Mantu,K; Lin,Y; Ringel,S,A, 2009, "Strain relaxation properties of InAsyP1-y metamorphic materials grown on InP substrates." JOURNAL OF APPLIED PHYSICS 105, no. 6, 061643 -
  • Yang,Chieh-Kai; Roblin,Patrick; Malonis,Andrew; Arehart,Aaron; Ringel,Steven; Poblenz,Christiane; Pei,Yi; Speck,James; Mishra,Umesh, 2009, "Characterization of Traps in AlGaN/GaN HEMTs with a Combined Large Signal Network Analyzer/Deep Level Optical Spectrometer System." 2009 IEEE/MTT-S INTERNATIONAL MICROWAVE SYMPOSIUM, VOLS 1-3 1-3, 1209 - 1212.

2008

  • Smith,P,E; LUECK,M; Ringel,S,A; BRILLSON,L,J, 2008, "Atomic diffusion and interface electronic structure at In0.49Ga0.51P/GaAs heterojunctions." JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 26, no. 1, 89 - 95.
  • Armstrong,A; Caudill,J; Corrion,A; Poblenz,C; Mishra,U,K; Speck,J,S; Ringel,S,A, 2008, "Characterization of majority and minority carrier deep levels in p-type GaN : Mg grown by molecular beam epitaxy using deep level optical spectroscopy." JOURNAL OF APPLIED PHYSICS 103, no. 6, 063722 -
  • Wilt,David,M; Pal,AnnaMaria,T; Ringel,Steven,A; Fitzgerald,Eugene,A; Jenkins,Phillip,P; Walters,Robert, 2008, "FINAL RESULTS FROM THE MISSE5 GaAs ON Si SOLAR CELL EXPERIMENT." PVSC: 2008 33RD IEEE PHOTOVOLTAIC SPECIALISTS CONFERENCE, VOLS 1-4 1-4, 2078 - 2081.
  • Arehart,A,R; Corrion,A; Poblenz,C; Speck,J,S; Mishra,U,K; Ringel,S,A, 2008, "Deep level optical and thermal spectroscopy of traps in n-GaN grown by ammonia molecular beam epitaxy." APPLIED PHYSICS LETTERS 93, no. 11, 112101 -
  • Lin,Y; Arehart,A,R; Carlin,A,M; Ringel,S,A, 2008, "Separation of bulk and surface electron transport in metamorphic InAs layers using quantitative mobility spectrum analysis." APPLIED PHYSICS LETTERS 93, no. 6, 062109 -
  • Arehart,A,R; Corrion,A; Poblenz,C; Speck,J,S; Mishra,U,K; DenBaars,S,P; Ringel,S,A, 2008, "Comparison of deep level incorporation in ammonia and rf-plasma assisted molecular beam epitaxy n-GaN films." PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 5, NO 6 5, no. 6, 1750 - 1752.

2007

  • Smith,P,E; LUECK,M; Ringel,S,A; BRILLSON,L,J, 2007, "Atomic diffusion and electronic structure in Al0.52In0.48P/GaAs heterostructures." JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 25, no. 6, 1916 - 1921.
  • Lin, Y.; Carlin, J. A.; Arehart, A. R.; Carlin, A. M.; Ringel, S. A., 2007, "High-mobility two-dimensional electron gas in InAlAs/InAs heterostructures grown on virtual InAs substrates by molecular-beam epitaxy." Applied Physics Letters 90, no. 1, NA -
  • Liu,Dongmin; Hudait,Mantu; Lin,Yong; Kim,Hyeongnam; Ringel,Steven,A; Lu,Wu, 2007, "Gate length scaling study of InAlAs/InGaAs/InAsP composite channel HEMTs." SOLID-STATE ELECTRONICS 51, no. 6, 838 - 841.
  • Mosbacker,H,L; El Hage,S; Gonzalez,M; Ringel,S,A; Hetzer,M; Look,D,C; Cantwell,G; Zhang,J; Song,J,J; BRILLSON,L,J, 2007, "Role of subsurface defects in metal-ZnO(0001) Schottky barrier formation." JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 25, no. 4, 1405 - 1411.
  • Liu,D; Hudait,M; Lin,Y; Ringel,S,A; Lu,W, 2007, "80nm In0.52Al0.48As/In0.53Ga0.47As/InAs0.3P0.7 composite channel HEMT with an f(T) of 280GHz." 2007 INTERNATIONAL SEMICONDUCTOR DEVICE RESEARCH SYMPOSIUM, VOLS 1 AND 2 1-2, 548 - 549.
  • Armstrong,Andrew; Chakraborty,Arpan; Speck,James,S; DenBaars,Steven,P; Mishra,Umesh,K; Ringel,Steven,A, 2007, "Characterization and discrimination of AlGaN- and GaN-related deep levels in AlGaN/GaN heterostructures." PHYSICS OF SEMICONDUCTORS, PTS A AND B 893, 223 - 224.
  • Armstrong,A; Poblenz,C; Mishra,U,K; Speck,J,S; Ringel,S,A, 2007, "Comparison of deep level spectra in p-type and n-type GaN grown by molecular beam epitaxy." PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 244, no. 6, 1867 - 1871.

2006

  • Armstrong, A.; Chakraborty, A.; Speck, J. S.; DenBaars, S. P.; Mishra, U. K.; Ringel, S. A., 2006, "Quantitative observation and discrimination of AlGaN- and GaN-related deep levels in AlGaN/GaN heterostructures using capacitance deep level optical spectroscopy." Applied Physics Letters 89, no. 26, NA -
  • Wilt,David,M; Ringel,Steven,A; Fitzgerald,Eugene,A; Jenkins,Phillip,P, 2006, "Preliminary on-orbit performance data from GaAs on Si solar cells aboard misses." CONFERENCE RECORD OF THE 2006 IEEE 4TH WORLD CONFERENCE ON PHOTOVOLTAIC ENERGY CONVERSION, VOLS 1 AND 2 1-2, 1915 - 1918.
  • Min Gao; Bradley, S. T.; Yu Cao; Jena, D.; Lin, Y.; Ringel, S. A.; Hwang, J.; Schaff, W. J.; Brillson, L. J., 2006, "Compositional modulation and optical emission in AlGaN epitaxial films." Journal of Applied Physics 100, no. 10, NA -
  • Lueck, M. R.; Andre, C. L.; Pitera, A. J.; Lee, M. L.; Fitzgerald, E. A.; Ringel, S. A., 2006, "Dual junction GaInP/GaAs solar cells grown on metamorphic SiGe/Si substrates with high open circuit voltage." IEEE Electron Device Letters 27, no. 3, 142 - 144.
  • Armstrong,A; Poblenz,C; Green,D,S; Mishra,U,K; Speck,J,S; Ringel,S,A, 2006, "Impact of substrate temperature on the incorporation of carbon-related defects and mechanism for semi-insulating behavior in GaN grown by molecular beam epitaxy." APPLIED PHYSICS LETTERS 88, no. 8, 082114 -
  • Liu, D.; Hudait, M.; Lin, Y.; Kim, H.; Ringel, S. A.; Lu, W., 2006, "In0.53Ga0.47As/InAs0.3P0.7 composite channel high electron mobility transistors." Electronics Letters 42, no. 5, NA -
  • Gonzalez, M.; Andre, C. L.; Walters, R. J.; Messenger, S. R.; Warner, J. H.; Lorentzen, J. R.; Pitera, A. J.; Fitzgerald, E. A.; Ringel, S. A., 2006, "Deep level defects in proton radiated GaAs grown on metamorphic SiGe/Si substrates." Journal of Applied Physics 100, no. 3, NA -
  • Arehart,A,R; Moran,B; Speck,J,S; Mishra,U,K; DenBaars,S,P; Ringel,S,A, 2006, "Effect of threading dislocation density on Ni/n-GaN Schottky diode I-V characteristics." JOURNAL OF APPLIED PHYSICS 100, no. 2, 023709 -
  • Kwon, O.; Boeckl, J. J.; Lee, M. L.; Pitera, A. J.; Fitzgerald, E. A.; Ringel, S. A., 2006, "Monolithic integration of AlGaInP laser diodes on SiGe/Si substrates by molecular beam epitaxy." Journal of Applied Physics 100, no. 1, NA -
  • Hudait, M. K.; Lin, Y.; Sinha, P. M.; Lindemuth, J. R.; Ringel, S. A., 2006, "Carrier compensation and scattering mechanisms in Si-doped InAsyP1-y layers grown on InP substrates using intermediate InAsyP1-y step-graded buffers." Journal of Applied Physics 100, no. 6, NA -

2005

  • Kwon, O.; Boeckl, J.; Lee, M. L.; Pitera, A. J.; Fitzgerald, E. A.; Ringel, S. A., 2005, "Growth and properties of AlGaInP resonant cavity light emitting diodes on Ge/SiGe/Si substrates." Journal of Applied Physics 97, no. 3, 034504 -
  • Armstrong, A.; Arehart, A.; Green, D.; Speck, J. S.; Mishra, U. K.; Ringel, S. A., 2005, "A novel method to investigate defect states in MBE grown highly resistive GaN doped with C and Si." Physica Status Solidi C 2, no. 7, 2411 - 2414.
  • Armstrong,A; Green,D; Arehart,A,R; Mishra,U,K; Speck,J,S; Ringel,S,A, 2005, "Carbon-related deep states in compensated n-type and semi-insulating GaN : C and their influence on yellow luminescence." GAN, AIN, INN AND THEIR ALLOYS 831, 311 - 316.
  • Kwon, O.; Lin, Y.; Boeckl, J.; Ringel, S. A., 2005, "Growth and properties of digitally-alloyed AlGaInP by solid source molecular beam epitaxy." Journal of Electronic Materials 34, no. 10, 1301 - 1306.
  • Liu,Dongmin; Hudait,Mantu; Lin,Yong; Kim,Hyeongnam; Ringel,Steven,A; Lu,Wu, 2005, "0.25 mu m In(0.52)A1(0.48)As/In0.53Ga0.47As/InAs0.3P0.7 composite channel HEMTs with an f(T) of 115GHz." 2005 ASIA-PACIFIC MICROWAVE CONFERENCE PROCEEDINGS, VOLS 1-5 1-5, 827 - 829.
  • Smith, P. E.; Goss, S. H.; Gao, M.; Hudait, M. K.; Lin, Y.; Ringel, S. A.; Brillson, L. J., 2005, "Atomic diffusion and band lineups at In0.53Ga0.47As-on-InP heterointerfaces." Journal of Vacuum Science & Technology B (Microelectronics and Nanometer Structures) 23, no. 4, 1832 - 1837.
  • LUECK,M; Gonzalez,M; Kwon,O; Andre,C; Ringel,S,A, 2005, "Impact of annealing and V : III ratio on properties of MBE grown wide-bandgap AIGaInP materials and solar cells." CONFERENCE RECORD OF THE THIRTY-FIRST IEEE PHOTOVOLTAIC SPECIALISTS CONFERENCE - 2005 31, 711 - 714.
  • Andre, C. L.; Carlin, J. A.; Boeckl, J. J.; Wilt, D. M.; Smith, M. A.; Pitera, A. J.; Lee, M. L.; Fitzgerald, E. A.; Ringel, S. A., 2005, "Investigations of high-performance GaAs solar cells grown on Ge-Si1-xGex-Si substrates." IEEE Transactions on Electron Devices 52, no. 6, 1055 - 1060.
  • Armstrong, A.; Arehart, A. R.; Ringel, S. A., 2005, "A method to determine deep level profiles in highly compensated, wide band gap semiconductors." Journal of Applied Physics 97, no. 8, 083529 -
  • Armstrong, A.; Arehart, A. R.; Green, D.; Mishra, U. K.; Speck, J. S.; Ringel, S. A., 2005, "Impact of deep levels on the electrical conductivity and luminescence of gallium nitride codoped with carbon and silicon." Journal of Applied Physics 98, no. 5, 053704 -
  • Tivarus, C.; Pelz, J. P.; Hudait, M. K.; Ringel, S. A., 2005, "Direct measurement of quantum confinement effects at metal to quantum-well nanocontacts." Physical Review Letters 94, no. 20, 206803 -
  • Andre, C. L.; Wilt, D. M.; Pitera, A. J.; Lee, M. L.; Fitzgerald, E. A.; Ringel, S. A., 2005, "Impact of dislocation densities on n+/p and p+/n junction GaAs diodes and solar cells on SiGe virtual substrates." Journal of Applied Physics 98, no. 1, 014502 -
  • Wilt,D,M; Pal,A,T; Prokop,N,F; Ringel,S,A; Andre,C,L; Smith,M,A; Scheiman,D,A; Jenkins,P,P; Maurer,W,F; McElroy,B; Fitzgerald,E,A, 2005, "Thermal cycle testing of GaAs on Si and metamorphic tandem on Si solar cells." CONFERENCE RECORD OF THE THIRTY-FIRST IEEE PHOTOVOLTAIC SPECIALISTS CONFERENCE - 2005 31, 571 - 574.
  • Tivarus, C.; Pelz, J. P.; Hudait, M. K.; Ringel, S. A., 2005, "Spatial resolution of ballistic electron emission microscopy measured on metal/quantum-well Schottky contacts." Applied Physics Letters 87, no. 18, 182105 -
  • Gao, M.; Lin, Y.; Bradley, S. T.; Ringel, S. A.; Hwang, J.; Schaff, W. J.; Brillson, L. J., 2005, "Spontaneous compositional superlattice and band-gap reduction in Si-doped AlxGa1-xN epilayers." Applied Physics Letters 87, no. 19, 191905 -
  • Ringel,S,A; Andre,C,L; Fitzgerald,E,A; Pitera,A,J; Wilt,D,M, 2005, "Multi-junction III-V photovoltaics on lattice-engineered Si sustrates." CONFERENCE RECORD OF THE THIRTY-FIRST IEEE PHOTOVOLTAIC SPECIALISTS CONFERENCE - 2005 31, 567 - 570.
  • Hudait, M. K.; Lin, Y.; Goss, S. H.; Smith, P.; Bradley, S.; Brillson, L. J.; Johnston, S. W.; Ahrenkiel, R. K.; Ringel, S. A., 2005, "Evidence of interface-induced persistent photoconductivity in InP/In0.53Ga0.47As/InP double heterostructures grown by molecular-beam epitaxy." Applied Physics Letters 87, no. 3, 032106 -
  • Lin, Y.; Hudait, M. K.; Johnston, S. W.; Ahrenkiel, R. K.; Ringel, S. A., 2005, "Photoconductivity decay in metamorphic InAsP/InGaAs double heterostructures grown on InAsyP1-y compositionally step-graded buffers." Applied Physics Letters 86, no. 7, 071908 -
  • Tivarus, C.; Park, K. -B.; Hudait, M. K.; Ringel, S. A.; Pelz, J. P., 2005, "Nanoscale characterization of metal/semiconductor nanocontacts." AIP Conference Proceedings no. 788,

2004

  • Armstrong, A.; Arehart, A. R.; Moran, B.; DenBaars, S. P.; Mishra, U. K.; Speck, J. S.; Ringel, S. A., 2004, "Impact of carbon on trap states in n-type GaN grown by metalorganic chemical vapor deposition." Applied Physics Letters 84, no. 3, 374 - 376.
  • Kwon,O; Boeckl,J; Lee,M,L; Pitera,A,J; Fitzgerald,E,A; Ringel,S,A, 2004, "Growth and properties of AlGaInP resonant cavity light emitting diodes (RCLEDs) on Ge/SiGe/Si substrates." PROGRESS IN COMPOUND SEMICONDUCTOR MATERIALS III - ELECTRONIC AND OPTOELECTRONIC APPLICATIONS 799, 161 - 166.
  • Andre, C. L.; Boeckl, J. J.; Wilt, D. M.; Pitera, A. J.; Lee, M. L.; Fitzgerald, E. A.; Keyes, B. M.; Ringel, S. A., 2004, "Impact of dislocations on minority carrier electron and hole lifetimes in GaAs grown on metamorphic SiGe substrates." Applied Physics Letters 84, no. 18, 3447 - 3449.
  • Hudait, M. K.; Lin, Y.; Palmisiano, M. N.; Tivarus, C.; Pelz, J. P.; Ringel, S. A., 2004, "Comparison of mixed anion, InAsyP1-y and mixed cation, InxAl1-xAs metamorphic buffers grown by molecular beam epitaxy on (100) InP substrates." Journal of Applied Physics 95, no. 8, 3952 - 3960.
  • Smith, P. E.; Goss, S. H.; Bradley, S. T.; Hudait, M. K.; Lin, Y.; Ringel, S. A.; Brillson, L. J., 2004, "Atomic layer diffusion and electronic structure at In0.53Ga0.47As/InP interfaces." Journal of Vacuum Science & Technology B (Microelectronics and Nanometer Structures) 22, no. 2, 554 - 559.

2003

  • Hudait, M. K.; Lin, Y.; Wilt, D. M.; Speck, J. S.; Tivarus, C. A.; Heller, E. R.; Pelz, J. P.; Ringel, S. A., 2003, "High-quality InAsyP1-y step-graded buffer by molecular-beam epitaxy." Applied Physics Letters 82, no. 19, 3212 - 3214.
  • Kwon, O.; Jazwiecki, M. M.; Sacks, R. N.; Ringel, S. A., 2003, "High-performance, metamorphic InxGa1-xAs tunnel diodes grown by molecular beam epitaxy." IEEE Electron Device Letters 24, no. 10, 613 - 615.
  • Armstrong,A; Arehart,A,R; Ringel,S,A; Moran,B; DenBaars,S,P; Mishra,U,K; Speck,J,S, 2003, "Identification of carbon-related bandgap states in GaN grown by MOCVD." GAN AND RELATED ALLOYS - 2003 798, 509 - 514.
  • Andre,C,L; Boeckl,J,J; Leitz,C,W; Currie,M,T; Langdo,T,A; Fitzgerald,E,A; Ringel,S,A, 2003, "Low-temperature GaAs films grown on Ge and Ge/SiGe/Si substrates." JOURNAL OF APPLIED PHYSICS 94, no. 8, 4980 - 4985.
  • Hudait, M. K.; Lin, Y.; Palmisiano, M. N.; Ringel, S. A., 2003, "0.6-eV bandgap In0.69Ga0.31As thermophotovoltaic devices grown on InAsyP1-y step-graded buffers by molecular beam epitaxy." IEEE Electron Device Letters 24, no. 9, 538 - 540.
  • Ringel,S,A; Andre,C,L; Hudait,M,K; Wilt,D,M; Clark,E,B; Pitera,A,J; Lee,M,L; Fitzgerald,E,A; Carroll,M; Erdtmann,M; CARLIN,E,B; Keyes,B,M, 2003, "Toward high performance N/P GaAs solar cells grown on low dislocation density p-type sige substrates." PROCEEDINGS OF 3RD WORLD CONFERENCE ON PHOTOVOLTAIC ENERGY CONVERSION, VOLS A-C A-C, 612 - 615.
  • Arehart,A,R; Poblenz,C; Heying,B; Speck,J,S; Mishra,U,K; DenBaars,S,P; Ringel,S,A, 2003, "Influence of growth parameters on the deep level spectrum in MBE-grown n-GaN." GAN AND RELATED ALLOYS - 2003 798, 735 - 740.

2002

  • Andre,C,L; Khan,A; Gonzalez,M; Hudait,M,K; Fitzgerald,E,A; Carlin,J,A; Currie,M,T; Leitz,C,W; Langdo,T,A; Clark,E,B; Wilt,D,M; Ringel,S,A, 2002, "Impact of threading dislocations on both n/p and p/n single junction GaAs cells grown on Ge/SiGe/Si substrates." CONFERENCE RECORD OF THE TWENTY-NINTH IEEE PHOTOVOLTAIC SPECIALISTS CONFERENCE 2002 29, 1043 - 1046.
  • Ringel, S. A.; Carlin, J. A.; Andre, C. L.; Hudait, M. K.; Gonzalez, M.; Wilt, D. M.; Clark, E. B.; Jenkins, P.; Scheiman, D.; Allerman, A.; Fitzgerald, E. A.; Leitz, C. W., 2002, "Single junction InGaP/GaAs solar cells grown on Si substrates with site buffer layers." Progress in Photovoltaics: Research and Applications 10, no. 6,
  • Kaplar,R,J; Ringel,S,A; Kurtz,S,R; Allerman,A,A; Klem,J,F, 2002, "Comparison of deep level spectra of MBE- and MOCVD-grown InGaAsN." DEFECT AND IMPURITY ENGINEERED SEMICONDUCTORS AND DEVICES III 719, 403 - 408.
  • Hudait, M. K.; Andre, C. L.; Kwon, O.; Palmisiano, M. N.; Ringel, S. A., 2002, "High-performance In0.53Ga0.47As thermophotovoltaic devices grown by solid source molecular beam epitaxy." IEEE Electron Device Letters 23, no. 12, 697 - 699.
  • Kaplar, R. J.; Ringel, S. A.; Kurtz, S. R.; Klem, J. F.; Allerman, A. A., 2002, "Deep-level defects in InGaAsN grown by molecular-beam epitaxy." Applied Physics Letters 80, no. 25, 4777 - 4779.
  • Hierro, A.; Arehart, A. R.; Heying, B.; Hansen, M.; Mishra, U. K.; DenBaars, S. P.; Speck, J. S.; Ringel, S. A., 2002, "Impact of Ga/N flux ratio on trap states in n-GaN grown by plasma-assisted molecular-beam epitaxy." Applied Physics Letters 80, no. 5, 805 - 807.

2001

  • Hierro, A.; Hansen, M.; Boeckl, J. J.; Zhao, L.; Speck, J. S.; Mishra, U. K.; DenBaars, S. P.; Ringel, S. A., 2001, "Carrier trapping and recombination at point defects and dislocations in MOCVD n-GaN." Physica Status Solidi B 228, no. 3, 937 - 946.
  • Kaplar, R. J.; Arehart, A. R.; Ringel, S. A.; Allerman, A. A.; Sieg, R. M.; Kurtz, S. R., 2001, "Deep levels and their impact on generation current in Sn-doped InGaAsN." Journal of Applied Physics 90, no. 7, 3405 - 340.
  • Kaplar, R. J.; Kwon, D.; Ringel, S. A.; Allerman, A. A.; Kurtz, S. R.; Jones, E. D.; Sieg, R. M., 2001, "Deep levels in p- and n-type InGaAsN for high-efficiency multi-junction III-V solar cells." Solar Energy Materials and Solar Cells 69, no. 1, 85 - 91.
  • Hierro,A; Arehart,A,R; Heying,B; Hansen,M; Speck,J,S; Mishra,U,K; DenBaars,S,P; Ringel,S,A, 2001, "Capture kinetics of electron traps in MBE-grown n-GaN." PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 228, no. 1, 309 - 313.
  • Carlin, J. A.; Ringel, S. A.; Fitzgerald, A.; Bulsara, M., 2001, "High-lifetime GaAs on Si using GeSi buffers and its potential for space photovoltaics." Solar Energy Materials and Solar Cells 66, no. 1-4, 621 - 630.

2000

  • Hierro, A.; Kwon, D.; Ringel, S. A.; Hansen, M.; Speck, J. S.; Mishra, U. K.; DenBarrs, S. P., 2000, "Optically and thermally detected deep levels in n-type Schottky and p+-n GaN diodes." Applied Physics Letters 76, no. 21, 3064 - 3066.
  • Hierro, A.; Kwon, D.; Ringel, S. A.; Rubini, S.; Pelucchi, E.; Franciosi, A., 2000, "Photocapacitance study of bulk deep levels in ZnSe grown by molecular-beam epitaxy." Journal of Applied Physics 87, no. 2, 730 - 738.
  • Hierro,A; Kwon,D; Ringel,S,A; Hansen,M; Mishra,U,K; DenBaars,S,P; Speck,J,S, 2000, "Deep levels in n-type Schottky and p(+)-n homojunction GaN diodes." MRS INTERNET JOURNAL OF NITRIDE SEMICONDUCTOR RESEARCH 5, U792 - U797.
  • Carlin, J. A.; Ringel, S. A.; Fitzgerald, E. A.; Bulsara, M.; Keyes, B. M., 2000, "Impact of GaAs buffer thickness on electronic quality of GaAs grown on graded Ge/GeSi/Si substrates." Applied Physics Letters 76, no. 14, 1884 - 1886.
  • Carlin, J. A.; Ringel, S. A.; Fitzgerald, E. A.; Bulsara, M., 2000, "High quality GaAs growth by MBE on Si using GeSi buffers and prospects for space photovoltaics." Progress in Photovoltaics: Research and Applications 8, no. 3,
  • Hierro, A.; Ringel, S. A.; Hansen, M.; Speck, J. S.; Mishra, U. K.; DenBaars, S. P., 2000, "Hydrogen passivation of deep levels in n-GaN." Applied Physics Letters 77, no. 10, 1499 - 1501.

1999

  • Clevenger, M. B.; Murray, C. S.; Ringel, S. A.; Sacks, R. N.; Qin, L.; Charache, G. W.; Depoy, D. M., 1999, "Optical properties of thin semiconductor device structures with reflective back-surface layers." AIP Conference Proceedings no. 460,
  • Kwon, D.; Kaplar, R. J.; Ringel, S. A.; Allerman, A. A.; Kurtz, S. R.; Jones, E. D., 1999, "Deep levels in p-type InGaAsN lattice matched to GaAs." Applied Physics Letters 74, no. 19, 2830 - 2832.
  • Ringel,S,A; Grillot,P,N, 1999, "Electronic properties and deep levels in germanium-silicon." GERMANIUM SILICON: PHYSICS AND MATERIALS 56, 293 - 346.
  • Sacks, R. N.; Qin, A.; Jazwiecki, M.; Ringel, S. A.; Clevenger, M. B.; Wilt, D.; Goorsky, M. S., 1999, "Growth and characterization of epitaxial FexAl1-x/(In,Al)As/InP and III-V/FexAl1-x/(In,Al)As/InP structures." Journal of Vacuum Science & Technology B (Microelectronics and Nanometer Structures) 17, no. 3, 1289 - 1293.
  • Xu, Q.; Hsu, J. W. P.; Carlin, J. A.; Sieg, R. M.; Boeckl, J. J.; Ringel, S. A., 1999, "Topographic and electronic studies of wedge-shape surface defects on AlGaAs/GaAs films grown on Ge substrates." Applied Physics Letters 75, no. 14, 2111 - 2113.
  • Hierro, A.; Kwon, D.; Goss, S. H.; Brillson, L. J.; Ringel, S. A.; Rubini, S.; Pelucchig, E.; Franciosi, A., 1999, "Evidence for a dominant midgap trap in n-ZnSe grown by molecular beam epitaxy." Applied Physics Letters 75, no. 6, 832 - 834.
  • Ringel, S. A.; Sacks, R. N.; Qin, L.; Clevenger, M. B.; Murray, C. S., 1999, "Growth and properties of InGaAs/FeAl/InAlAs/InP heterostructures for buried reflector/interconnect applications in InGaAs thermophotovoltaic devices." AIP Conference Proceedings no. 460,

1998

  • Anderson, B. L.; Pelz, L. J.; Ringel, S. A.; Clymer, B. D.; Collins, S. A. , Jr., 1998, "Photonics laboratory with emphasis on technical diversity." IEEE Transactions on Education 41, no. 3, 194 - 202.
  • Sieg, R. M.; Carlin, J. A.; Ringel, S. A.; Currie, M. T.; Ting, S. M.; Langdo, T. A.; Taraschi, G.; Fitzgerald, E. A.; Keyes, B. M., 1998, "High minority-carrier lifetimes in GaAs grown on low-defect-density Ge/GeSi/Si substrates." Applied Physics Letters 73, no. 21, 3111 - 3113.
  • Sieg, R. M.; Ringel, S. A.; Ting, S. M.; Fitzgerald, E. A.; Sacks, R. N., 1998, "Anti-phase domain-free growth of GaAs on offcut (001) Ge wafers by molecular beam epitaxy with suppressed Ge outdiffusion." Journal of Electronic Materials 27, no. 7, 900 - 907.
  • Ringel, S. A.; Chatterjee, B., 1998, "Electrical deactivation of interstitial Zn in heteroepitaxial InP by hydrogen and its effect on electronic properties." Journal of Applied Physics 83, no. 11, 5904 - 591.
  • Xu, Q.; Hsu, J. W. P.; Ting, S. M.; Fitzgerald, E. A.; Sieg, R. M.; Ringel, S. A., 1998, "Scanning force microscopy studies of GaAs films grown on offcut Ge substrates." Journal of Electronic Materials 27, no. 9, 1010 - 1016.
  • Ting, S. M.; Fitzgerald, E. A.; Sieg, R. M.; Ringel, S. A., 1998, "Range of defect morphologies on GaAs grown on offcut (001) Ge substrates." Journal of Electronic Materials 27, no. 5, 451 - 461.
  • Carlin, J. A.; Ringel, S. A.; Sacks, R. N.; Yap, K. S., 1998, "Role of Al content on surface structure evolution of low temperature AlxGa1-xAs and its effect on critical thickness." Journal of Vacuum Science & Technology B (Microelectronics and Nanometer Structures) 16, no. 3, 1372 - 1376.
  • Sieg, R. M.; Ringel, S. A.; Ting, S. M.; Samavedam, S. B.; Currie, M.; Langdo, T.; Fitzgerald, E. A., 1998, "Toward device-quality GaAs growth by molecular beam epitaxy on offcut Ge/Si1-xGex/Si substrates." Journal of Vacuum Science & Technology B (Microelectronics and Nanometer Structures) 16, no. 3, 1471 - 1474.

1997

  • Ringel, S. A.; Chatterjee, B.; Hoffman, R. W. , Jr., 1997, "Hydrogen passivation of interstitial Zn defects in hetero-epitaxial InP cell structures and influence on device characteristics." Progress in Photovoltaics: Research and Applications 5, no. 6,
  • Sieg, R. M.; Sacks, R. N.; Ringel, S. A., 1997, "Application of pyrometric interferometry to the in situ monitoring of In0.52Al0.48As, In0.53Ga0.47As, and quaternary alloy growth on InP substrates." Journal of Crystal Growth 175-176,
  • Ringel, S. A., 1997, "Hydrogen-extended defect interactions in heteroepitaxial InP materials and devices." Solid-State Electronics 41, no. 3, 359 - 380.
  • Hoffman, R. W.; Fatemi, N. S.; Weizer, V. G.; Jenkins, P. P.; Stan, M. A.; Ringel, S. A.; Scheiman, D. A.; Wilt, D. M.; Brinker, D. J., 1997, "High beginning-of-life efficiency p/n InP solar cells." Progress in Photovoltaics: Research and Applications 5, no. 6,

1996

  • Chatterjee, B.; Ringel, S. A., 1996, "Effect of extended defects on the formation and dissociation kinetics of Zn-H complexes in heteroepitaxial p-type InP layers." Applied Physics Letters 69, no. 6, 839 - 841.
  • Grillot, P. N.; Ringel, S. A., 1996, "Identification of compositionally invariant deep levels introduced by plastic strain in epitaxial Ge0.30Si0.70 and deformed bulk Si." Applied Physics Letters 69, no. 14, 2110 - 2112.
  • Sieg, R. M.; Ringel, S. A., 1996, "Reabsorption, band-gap narrowing, and the reconciliation of photoluminescence spectra with electrical measurements for epitaxial n-InP." Journal of Applied Physics 80, no. 1, 448 - 458.
  • Sieg,R,M; Sacks,R,N; Grillot,P,N; Ringel,S,A, 1996, "Improved substrate temperature stability during molecular beam epitaxy growth using indium free mounting of small substrates of various shapes." JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 14, no. 6, 3283 - 3287.
  • Grillot, P. N.; Ringel, S. A.; Fitzgerald, E. A., 1996, "Effect of composition on deep levels in heteroepitaxial GexSi1-x layers and evidence for dominant intrinsic recombination-generation in relaxed Ge layers on Si." Journal of Electronic Materials 25, no. 7, 1028 - 1036.
  • Grillot, P. N.; Ringel, S. A.; Michel, J.; Fitzgerald, E. A., 1996, "Structural, electronic, and luminescence investigation of strain-relaxation induced electrical conductivity type conversion in GeSi/Si heterostructures." Journal of Applied Physics 80, no. 5, 2823 - 2832.
  • Chatterjee, B.; Ringel, S. A.; Hoffman, R. , Jr., 1996, "Hydrogen passivation of n+p and p+n heteroepitaxial InP solar cell structures." Progress in Photovoltaics: Research and Applications 4, no. 2,
  • Sacks, R. N.; Sieg, R. M.; Ringel, S. A., 1996, "Investigation of the accuracy of pyrometric interferometry in determining AlxGa1-xAs growth rates and compositions." Journal of Vacuum Science & Technology B (Microelectronics and Nanometer Structures) 14, no. 3, 2157 - 2162.

1995

  • Mena, R. A.; Schacham, S. E.; Haugland, E. J.; Alterovitz, S. A.; Bibyk, S. B.; Ringel, S. A., 1995, "Subband quantum scattering times for AlGaAs/GaAs obtained using digital filtering." Journal of Applied Physics 78, no. 6, 3940 - 3944.
  • Chatterjee, B.; Ringel, S. A., 1995, "Hydrogen passivation and its effects on carrier trapping by dislocations in InP/GaAs heterostructures." Journal of Applied Physics 77, no. 8, 3885 - 3898.
  • Mena, R. A.; Schacham, S. E.; Haugland, E. J.; Alterovitz, S. A.; Young, P. G.; Bibyk, S. B.; Ringel, S. A., 1995, "Characterization of the transport properties of channel delta-doped structures by light-modulated Shubnikov-de Haas measurements." Journal of Applied Physics 78, no. 11, 6626 - 6632.
  • Sieg, R. M.; Chatterjee, B.; Ringel, S. A., 1995, "Evidence for enhanced zinc interstitial concentration in strain-relaxed heteroepitaxial indium phosphide." Applied Physics Letters 66, no. 23, 3108 - 3110.
  • Grillot, P. N.; Ringel, S. A.; Fitzgerald, E. A.; Watson, G. P.; Xie, Y. H., 1995, "Minority- and majority-carrier trapping in strain-relaxed Ge0.3Si0.7/Si heterostructure diodes grown by rapid thermal chemical-vapor deposition." Journal of Applied Physics 77, no. 2, 686 - 685.
  • Grillot, P. N.; Ringel, S. A.; Fitzgerald, E. A.; Watson, G. P.; Xie, Y. H., 1995, "Electron trapping kinetics at dislocations in relaxed Ge0.3Si0.7/Si heterostructures." Journal of Applied Physics 77, no. 7, 3248 - 3256.

1994

  • Chatterjee, B.; Ringel, S. A.; Sieg, R.; Hoffman, R.; Weinberg, I., 1994, "Hydrogen passivation of dislocations in InP on GaAs heterostructures." Applied Physics Letters 65, no. 1, 58 - 60.

1991

  • Ringel, S. A.; Smith, A. W.; MacDougal, M. H.; Rohatgi, A., 1991, "The effects of CdCl2 on the electronic properties of molecular-beam epitaxially grown CdTe/CdS heterojunction solar cells." Journal of Applied Physics 70, no. 2, 881 - 889.
  • Rohatgi, A.; Sudharsanan, R.; Ringel, S. A.; MacDougal, M. H., 1991, "Growth and process optimization of CdTe and CdZnTe polycrystalline films for high efficiency solar cells." Solar Cells 30, no. 1-4, 109 - 122.
  • Ringel, S. A.; Rohatgi, A., 1991, "The effects of trap-induced lifetime variations on the design and performance of high-efficiency GaAs solar cells." IEEE Transactions on Electron Devices 38, no. 11, 2402 - 2409.

1990

  • Ringel, S. A.; Sudharsanan, R.; Rohatgi, A.; Carter, W. B., 1990, "A study of polycrystalline Cd(Zn,Mn)Te/CdS films and interfaces." Journal of Electronic Materials 19, no. 3, 259 - 263.
  • Ringel, S. A.; Sudharsanan, R.; Rohatgi, A.; Owens, M. S.; Gillis, H. P., 1990, "Effects of annealing and surface preparation on the properties of polycrystalline CdZnTe films grown by molecular beam epitaxy." Journal of Vacuum Science & Technology A (Vacuum, Surfaces, and Films) 8, no. 3, 2012 - 2019.

1989

  • Ringel, S. A.; Rohatgi, A.; Tobin, S. P., 1989, "An approach toward 25-percent efficient GaAs heteroface solar cells." IEEE Transactions on Electron Devices 36, no. 7, 1230 - 1237.
  • Rohatgi, A.; Ringel, S. A.; Sudharsanan, R.; Meyers, P. V.; Liu, C. H.; Ramanathan, V., 1989, "Investigation of polycrystalline CdZnTe, CdMnTe, and CdTe films for photovoltaic applications." Solar Cells 27, no. 1-4,

1988

  • DeWald, A. B.; Frost, R. L.; Ringel, S. A.; Schaffer, J. P.; Rohatgi, A.; Nielsen, B.; Lynn, K. G., 1988, "Positron annihilation spectroscopy of AlGaAs/GaAs interfaces in metalorganic chemical vapor deposition grown GaAs heterojunction solar cells." Journal of Vacuum Science & Technology A (Vacuum, Surfaces, and Films) 6, no. 4, 2248 - 2252.
  • Rohatgi, A.; Ringel, S. A.; Welch, J.; Meeks, E.; Pollard, K.; Erbil, A.; Summers, C. J.; Meyers, P. V.; Liu, C. H., 1988, "Growth and characterization of CdMnTe and CdZnTe polycrystalline thin films for solar cells." Solar Cells 24, no. 1-2, 185 - 194.

1987

  • Ringel, S. A.; Ashok, S., 1987, "Silicon surface barrier modification by low-energy nitrogen ion implantation." Journal of the Electrochemical Society 134, no. 6, 1494 - 1499.

1986

  • Ringel, S. A.; Chien, H. C.; Ashok, S., 1986, "Evidence for the formation of polycrystalline silicon by argon implantation and its passivation by atomic hydrogen." Applied Physics Letters 49, no. 12, 728 - 730.
  • Ashok, S.; Ringel, S. A., 1986, "Low-energy hydrogen implantation for silicon Schottky barrier modification." Vacuum 36, no. 11-12, 917 - 920.
  • Giewont, K.; Ringel, S. A.; Ashok, S., 1986, "Synergistic effects in ion bombardment modification of silicon Schottky contacts." Journal of Vacuum Science & Technology A (Vacuum, Surfaces, and Films) 4, no. 3,
  • Ringel, S. A.; Mu, X. C.; Fonash, S. J.; Ashok, S., 1986, "A study of target heating in low-energy ion-beam processing." Journal of Vacuum Science & Technology A (Vacuum, Surfaces, and Films) 4, no. 5, 2385 - 2388.

Papers in Proceedings

2012

  • Sasikumar,A; Arehart,A; Ringel,S,A; Kaun,S; Wong,M,H; Mishra,U,K; Speck,J,S "Direct Correlation Between Specific Trap Formation and Electric Stress-induced Degradation in MBE-grown AlGaN/GaN HEMTs." in IEEE International Reliability Physics Symposium (IRPS). Piscataway, (1 2012). 2C.3.1 - 2C.3.6.