Dr. Sudersena Rao Tatavarti Profile

Dr. Sudersena Rao Tatavarti

at MicroLink Devices Inc

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Publications (6)

Proceedings Article | 4 March 2022 Presentation + Paper

Light management for improved photon absorption in thin-film radiation-tolerant multijunction space photovoltaics

Julia D'Rozario, Steve Polly, Rao Tatavarti, Seth Hubbard

Proceedings Volume 11996, 1199605 (2022) https://doi.org/10.1117/12.2609780

KEYWORDS: Solar cells, Indium gallium arsenide, Reactive ion etching, Reflectivity, Thin films, Absorption, Mirrors, Photovoltaics, Gallium arsenide, Thin film solar cells

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Proceedings Article | 9 March 2021 Presentation

Improved photon absorption in thin-film solar cells for integration into radiation tolerant multijunction photovoltaics

Seth Hubbard, Julia D'Rozario, Stephen Polly, S. Rao Tatavarti

Proceedings Volume 11681, 116810M (2021) https://doi.org/10.1117/12.2590964

KEYWORDS: Tolerancing, Solar radiation, Multijunction solar cells, Mirrors, Indium gallium arsenide, Solar cells, Diffusion, Wet etching, Solar energy, Resistance

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Proceedings Article | 14 March 2016 Paper

Carrier dynamics in QW and bulk bismide and epitaxial lift off GaAs-In(Al)GaP double heterostructures grown by MOVPE for multi-junction solar cells

Yongkun Sin, Mark Peterson, Zachary Lingley, Stephen LaLumondiere, Steven Moss, Honghyuk Kim, Kamran Forghani, Yingxin Guan, Kangho Kim, Jaejin Lee, Luke Mawst, Thomas Kuech, Rao Tatavarti

Proceedings Volume 9743, 974313 (2016) https://doi.org/10.1117/12.2208804

KEYWORDS: Carrier dynamics, Quantum wells, Indium gallium phosphide, Multijunction solar cells, Heterojunctions, Gallium arsenide, Annealing, Epitaxial lateral overgrowth, Luminescence, Bismuth, Solar cells, Tellurium, Ions, Transmission electron microscopy

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III-V multi-junction solar cells are based on a triple-junction design that consists of an InGaP top junction, a GaAs middle junction, and a bottom junction that employs either a 1eV material grown on the GaAs substrate or InGaAs grown on the Ge substrate. The most promising 1 eV materials under extensive investigation are the bulk dilute nitride such as InGaAsN(Sb) lattice-matched to GaAs substrate and the dilute-bismide quantum well materials, such as GaAsBi, strain-compensated with GaAsP barriers. Both approaches have the potential to achieve high performance triple-junction solar cells. In addition, space satellite applications utilizing III-V triple-junction solar cells can have significantly reduced weight and high efficiency. An attractive approach to achieve these goals is to employ full-wafer epitaxial lift off (ELO) technology, which can eliminate the substrate weight and also enable multiple substrate re-usages. For the present study, we employed time-resolved photoluminescence (TR-PL) techniques to study carrier dynamics in MOVPE-grown bulk dilute bismide double heterostructures (DH). Carrier lifetime measurements are crucial to optimizing MOVPE materials growth. We have studied carrier dynamics in GaAsBi QW structures with GaAsP barriers. Carrier lifetimes were measured from GaAsBi DH samples at different stages of post-growth thermal annealing steps. Post-growth annealing yielded significant improvements in carrier lifetimes. Based on this study, single junction solar cells (SJSC) were grown and annealed under a variety of conditions and characterized. The SJSC annealed at 600 – 650 °C exhibited improved response in EQE spectra. In addition, we studied carrier dynamics in MOVPE-grown GaAs-In(Al)GaP DH samples grown on GaAs substrates. The structures were grown on top of a thin AlAs release layer, which allowed epitaxial layers grown on top of the AlAs layer to be removed from the substrate. The GaAs active layers had various doping densities and thicknesses. Our TR-PL results from both pre- and post-ELO processed GaAs-In(Al)GaP DH samples are reported.

Proceedings Article | 16 April 2015 Paper

Radiative dark current in optically thin III-V photovoltaic devices

Roger Welser, Ashok Sood, Sudersena Rao Tatavarti, Andree Wibowo, David Wilt, Alex Howard

Proceedings Volume 9358, 93580Q (2015) https://doi.org/10.1117/12.2185571

KEYWORDS: Quantum wells, Photovoltaics, Indium gallium arsenide, Diodes, Solar cells, External quantum efficiency, Thin films, Epitaxial lateral overgrowth, Gallium arsenide, Absorption

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Proceedings Article | 25 March 2013 Paper

Carrier dynamics in bulk 1eV InGaAsNSb materials and epitaxial lift off GaAs-InAlGaP layers grown by MOVPE for multi-junction solar cells

Yongkun Sin, Stephen LaLumondiere, William Lotshaw, Steven Moss, Tae Wan Kim, Kamran Forghani, Luke Mawst, Thomas Kuech, Rao Tatavarti, Andree Wibowo, Noren Pan

Proceedings Volume 8620, 86201L (2013) https://doi.org/10.1117/12.2001528

KEYWORDS: Epitaxial lateral overgrowth, Gallium arsenide, Carrier dynamics, Picosecond phenomena, Antimony, Multijunction solar cells, Solar cells, Zinc, Electroluminescence, Annealing

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III-V multi-junction solar cells are based on a triple-junction design that consists of an InGaP top junction, a GaAs middle junction, and a bottom junction that employs either a 1eV material grown on the GaAs substrate or InGaAs grown on the Ge substrate. The most promising 1 eV material that is currently under extensive investigation is bulk dilute nitride such as InGaAsN(Sb) lattice matched to GaAs substrates. Both approaches utilizing dilute nitrides and lattice-mismatched InGaAs layers have a potential to achieve high performance triple-junction solar cells. In addition, it will be beneficial for both commercial and space applications if III-V triple-junction solar cells can significantly reduce weight and can be manufactured cost effectively while maintaining high efficiency. The most attractive approach to achieve these goals is to employ full-wafer epitaxial lift off (ELO) technology, which can eliminate the substrate weight and also enable multiple substrate re-usages. For the present study, we employed time-resolved photoluminescence (TR-PL) techniques to study carrier dynamics in MOVPE-grown bulk dilute nitride layers lattice matched to GaAs substrates, where carrier lifetime measurements are crucial in optimizing MOVPE materials growth. We studied carrier dynamics in InGaAsN(Sb) layers with different amounts of N incorporated. Carrier lifetimes were also measured from InGaAsN(Sb) layers at different stages of post-growth thermal annealing steps. Post-growth annealing yielded significant improvements in carrier lifetimes of InGaAsNSb double hetero-structure (DH) samples compared to InGaAsN DH samples possibly due to the surfactant effect of Sb. In addition, we studied carrier dynamics in MOVPE-grown GaAs-InAl(Ga)P layers grown on GaAs substrates. The structures were grown on top of a thin AlAs release layer, which allowed epitaxial layers grown on top of the AlAs layer to be removed from the substrate. The GaAs layers had various doping densities and thicknesses. We present our TR-PL results from both pre- and post-ELO processed GaAs-InAl(Ga)P samples.

Proceedings Article | 21 August 2009 Paper

Light weight low cost InGaP/GaAs dual-junction solar cells on 4" epitaxial liftoff (ELO) wafers

Rao Tatavarti, G. Hillier, C. Youtsey, D. McCallum, G. Martin, A. Wibowo, R. Navaratnarajah, F. Tuminello, D. Hertkorn, M. Disabb, N. Pan

Proceedings Volume 7407, 74070B (2009) https://doi.org/10.1117/12.827449

KEYWORDS: Epitaxial lateral overgrowth, Solar cells, Semiconducting wafers, Gallium arsenide, Electroluminescence, Indium gallium phosphide, Quantum efficiency, Metals, Transmission electron microscopy, Antireflective coatings

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