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Conferences

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)

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.