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Steven Ringel

  • Executive Director - IMR, OR - Inst for Material Res
  • Professor, Neal A Smith Chair, Electrical & Computer Engr.
  • Professor, Materials Science Engineering
  • Professor, Physics
  • 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

http://emdl.ece.ohio-state.edu/index.html

Honors

  • 2005

    AAAS Fellow.

  • 1999

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

  • 1994

    National Young Investigator Award.

Chapters

2006

  • Wilt, D. M.; Ringel, S. A.; Fitzgerald, E. A.; Jenkins, P. P.; Walters, R.. 2006. In Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion (IEEE Cat. No. 06CH37747), IEEE.
  • Lee, K.; VanMil, B.; Luo, M.; Myers, T. H.; Armstrong, A.; Ringel, S. A.; Rummukainen, M.; Saarinen, K.. 2006. In GaN, AlN, InN and Related Materials. Symposium (Materials Research Society Symposium Proceedings Vol.892), Materials Research Society.
  • Ringel, S. A.; Kwon, O.; Lueck, M.; Boeckl, J.; Fitzgerald, E. A.. 2006. In 2006 International SiGe Technology and Device Meeting (IEEE Cat. No. 06EX1419), IEEE.
  • Liu, D.; Hudait, M.; Lin, Y.; Kim, H.; Ringel, S. A.; Lu, W.. 2006. In 2005 Asia-Pacific Microwave Conference, IEEE.

2005

  • Dongmin Liu; Hudait, M.; Yong Lin; Hyeongnam Kim; Ringel, S. A.; Wu Lu. 2005. In 2005 International Semiconductor Device Research Symposium (IEEE Cat. No.05EX1272C), IEEE.
  • Wilt, D. M.; Pal, A. M. T.; Prokop, N. F.; Ringel, S. A.; Andre, Cl.; Smith, M. A.; Scheiman, D. A.; Jenkins, P. P.; Maurer, W. F.; McElroy, B.; Fitzgerald, E. A.. 2005. In Conference Record of the Thirty-First IEEE Photovoltaic Specialist Conference (IEEE Cat. No. 05CH37608), IEEE.
  • Ringel, S. A.; Andre, C. L.; Lueck, M.; Isaacson, D.; Pitera, A. J.; Fitzgerald, E. A.; Wilt, D. M.. 2005. In Materials for Photovoltaics. Symposium (Materials Research Society Symposium Proceedings Vol.836), Materials Research Society.
  • Lueck, M.; Gonzalez, M.; Ojin Kwon; Andre, C.; Ringel, S. A.. 2005. In Conference Record of the Thirty-First IEEE Photovoltaic Specialist Conference (IEEE Cat. No. 05CH37608), IEEE.
  • Ringel, S. A.; Andre, C. L.; Fitzgerald, E. A.; Pitera, A. J.; Wilt, D. M.. 2005. In Conference Record of the Thirty-First IEEE Photovoltaic Specialist Conference (IEEE Cat. No. 05CH37608), IEEE.
  • Armstrong, A.; Green, D.; Arehart, A. R.; Mishra, U. K.; Speck, J. S.; Ringel, S. A.. 2005. In GaN, AlN, InN and Their Alloys. Symposium (Materials Research Society Symposium Proceedings Vol.831), Materials Research Society.

2004

  • Armstrong, A.; Arehart, A. R.; Ringel, S. A.; Moran, B.; Denbaars, S. P.; Mishra, U. K.; Speck, J. S.. 2004. In GaN and Related Alloys - 2003 Symposium (Mater. Res. Soc. Symposium Proceedings Vol.798), Mater. Res. Soc.
  • Arehart, A. R.; Poblenz, C.; Heying, B.; Speck, J. S.; Mishra, U. K.; DenBaars, S. P.; Ringel, S. A.. 2004. In GaN and Related Alloys - 2003 Symposium (Mater. Res. Soc. Symposium Proceedings Vol.798), Mater. Res. Soc.
  • Armstrong, A.; Arehart, A. R.; Moran, B.; DenBaars, S. P.; Mishra, U. K.; Speck, J. S.; Ringel, S. A.. 2004. In 2003 International Symposium on Compound Semiconductors: Post-Conference Proceedings (IEEE Cat. No.03TH8767), IEEE.

2003

  • 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, J. A.; Keyes, B. M.. 2003. In Proceedings of 3rd World Conference on Photovoltaic Energy Conversion (IEEE Cat. No.03CH37497), Arisumi Printing Inc.
  • Fitzgerald, E. A.; Groenart, M. E.; Pitera, A.; Lee, M. L.; Yang, V.; Carlin, J. A.; Leitz, C. W.; Andre, C. L.; Ringel, S. A.. 2003. In Proceedings of 3rd World Conference on Photovoltaic Energy Conversion (IEEE Cat. No.03CH37497), Arisumi Printing Inc.
  • Ringel, S. A.; Armstrong, A.; Arehart, A.; Moran, B.; Mishra, U. K.; Speck, J. S.. 2003. In 2003 International Symposium on Compound Semiconductors (Cat. No.03TH8675), IEEE.

2002

  • Hudait, M. K.; Lin, Y.; Andre, C. L.; Sinha, P. M.; Tivarus, C. A.; Pelz, J. P.; Wilt, D. M.; Ringel, S. A.. 2002. In Materials and Devices for Optoelectronics and Microphotonics. Symposia (Materials Research Society Symposium Proceedings Vol.722), Mater. Res. Soc.
  • 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. In Conference Record of the Twenty-Ninth IEEE Photovoltaic Specialists Conference 2002 (Cat. No.02CH37361), IEEE.

2000

  • Hierro, A.; Kwon, D.; Ringel, S. A.; Hansen, M.; Mishra, U. K.; DenBaars, S. P.; Speck, J. S.. 2000. In GaN and Related Alloys - 1999. Symposium (Materials Research Society Symposium Proceedings Vol.595), Mater. Res. Soc.
  • Carlin, J. A.; Hudait, M. K.; Ringel, S. A.; Wilt, D. M.; Clark, E. B.; Leitz, C. W.; Currie, M.; Langdo, T.; Fitzgerald, E. A.. 2000. In Conference Record of the Twenty-Eighth IEEE Photovoltaic Specialists Conference - 2000 (Cat. No.00CH37036), IEEE.
  • Hierro, A.; Boeckl, J. J.; Ringel, S. A.; Hansen, M.; Mishra, U. K.; Debaars, S. P.; Speck, J. S.; Look, D. C.. 2000. In Proceedings of International Workshop on Nitride Semiconductors, Inst. Pure & Appl. Phys.

1999

  • Daewon Kwon; Kaplar, R. J.; Beockl, J. J.; Ringel, S. A.; Allerman, A. A.; Kurtz, S. R.; Jones, E. D.. 1999. In III-V and IV-IV Materials and Processing Challenges for Highly Integrated Microelectronics and Optoelectronics. Symposium, Materials Res. Soc.
  • Ringel, S. A.; Carlin, J. A.; Sieg, R. M.; Boeckl, J. J.; Fitzgerald, E. A.. 1999. In Lattice Mismatched Thin Films. Proceedings of the First International Workshop, TMS - Miner. Metals & Mater. Soc.
  • Hierro, A.; Kwon, D.; Ringel, S. A.; Brillson, L. J.; Young, A. P.; Franciosi, A.. 1999. In III-V and IV-IV Materials and Processing Challenges for Highly Integrated Microelectronics and Optoelectronics. Symposium, Materials Res. Soc.

1998

  • Hoffman, R. W. , Jr.; Fatemi, N. S.; Weizer, V. G.; Jenkins, P.; Stan, M. A.; Ringel, S. A.; Sieg, R. M.; Scheiman, D. A.; Wilt, D. M.; Brinker, D. J.. 1998. In Thin-Film Structures for Photovoltaics. Symposium, Materials Research Society.

1997

  • Ringel, S. A.; Grillot, P. N.. 1997. In Defects in Electronic Materials II. Symposium, Mater. Res. Soc.
  • Ringel, S. A.; Sieg, R. M.; Ting, S. M.; Fitzgerald, E. A.. 1997. In Conference Record of the Twenty Sixth IEEE Photovoltaic Specialists Conference - 1997 (Cat. No.97CB36026), IEEE.
  • Chatterjee, B.; Ringel, S. A.; Hoffman, R. W. , Jr.. 1997. In Conference Record of the Twenty Sixth IEEE Photovoltaic Specialists Conference - 1997 (Cat. No.97CB36026), IEEE.
  • Hoffman, R. W. , Jr.; Fatemi, N. S.; Jenkins, P. P.; Weizer, V. G.; Stan, M. A.; Ringel, S. A.; Scheiman, D. A.; Wilt, D. M.; Brinker, D. J.; Walters, R. J.; Messenger, S. R.. 1997. In Conference Record of the Twenty Sixth IEEE Photovoltaic Specialists Conference - 1997 (Cat. No.97CB36026), IEEE.

1996

  • Chatterjee, B.; Ringel, S. A.; Hoffman, R. , Jr.. 1996. In Conference Record of the Twenty Fifth IEEE Photovoltaic Specialists Conference - 1996 (Cat. No.96CH35897), IEEE.
  • Hoffman, R. W. , Jr.; Fatemi, N. S.; Jenkins, P. P.; Scheiman, D. A.; Ringel, S. A.; Davis, W.; Weizer, V. G.; Wilt, D. M.; Brinker, D. J.. 1996. In Conference Record of the Twenty Fifth IEEE Photovoltaic Specialists Conference - 1996 (Cat. No.96CH35897), IEEE.

1994

  • Grillot, P. N.; Ringel, S. A.; Watson, G. P.; Fitzgerald, E. A.; Xie, Y. H.. 1994. In Physics and Applications of Defects in Advanced Semiconductors. Symposium, Mater. Res. Soc.
  • Chatterjee, B.; Ringel, S. A.; Sieg, R.; Weinberg, I.; Hoffman, R.. 1994. In Physics and Applications of Defects in Advanced Semiconductors. Symposium, Mater. Res. Soc.
  • Ringel, S. A.; Chatterjee, B.; Sieg, R. M.; Schnetzer, E. V.; Hoffman, R.. 1994. In 1994 IEEE First World Conference on Photovoltaic Energy Conversion. Conference Record of the Twenty Fourth IEEE Photovoltaic Specialists Conference-1994 (Cat.No.94CH3365-4), IEEE.

1991

  • Rohatgi, A.; Ringel, S. A.; Sudharsanan, R.; Chou, H. C.. 1991. In Conference Record of the Twenty Second IEEE Photovoltaic Specialists Conference - 1991 (Cat. No.91CH2953-8), IEEE.

1988

  • Ringel, S. A.; Rohatgi, A.. 1988. In Conference Record of the Twentieth IEEE Photovoltaic Specialists Conference - 1988 (Cat. No.88CH2527-0), IEEE.
  • Rohatgi, A.; Sudharsanan, R.; Ringel, S. A.; Meyers, P. V.; Liu, C. H.. 1988. In Conference Record of the Twentieth IEEE Photovoltaic Specialists Conference - 1988 (Cat. No.88CH2527-0), IEEE.

Journal Articles

2007

  • 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,

2006

  • 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,
  • 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,
  • 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,
  • 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,
  • 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,
  • 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,
  • 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,

2005

  • 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,
  • 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,
  • 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,
  • 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,
  • 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,
  • 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,
  • 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,
  • 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,
  • 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,
  • 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,
  • 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,
  • 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,
  • 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 no. 7,
  • 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,

2004

  • 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,
  • 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,
  • 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,
  • 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,

2003

  • 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,
  • 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,
  • 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,

2002

  • 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,
  • 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,
  • 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,
  • 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,

2001

  • 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,
  • 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,
  • 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,
  • 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,

2000

  • 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,
  • 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,
  • 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,
  • 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,
  • 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,

1999

  • 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,
  • 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,
  • 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,
  • 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,
  • 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,

1998

  • 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,
  • 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,
  • 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,
  • 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,
  • 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,
  • 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,
  • 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,
  • 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,

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,
  • 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,
  • Ringel, S. A., 1997, "Hydrogen-extended defect interactions in heteroepitaxial InP materials and devices." Solid-State Electronics 41, no. 3,
  • 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,

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,
  • 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,
  • 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,
  • 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,
  • 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,
  • 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,
  • 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,

1995

  • 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,
  • 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,
  • 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,
  • 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,
  • 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,
  • 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,

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,

1991

  • 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,
  • 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,
  • 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,

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,
  • 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,

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,
  • 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,
  • 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,

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,

1986

  • Ashok, S.; Ringel, S. A., 1986, "Low-energy hydrogen implantation for silicon Schottky barrier modification." Vacuum 36, no. 11-12,
  • 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,
  • 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.; 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,