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Your search keyword '"Polly, Stephen"' showing total 87 results
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87 results on '"Polly, Stephen"'

4. Development of MOVPE grown GaSb-on-GaAs interfacial misfit solar cells.

Author

Kessler-Lewis, Emily S., Polly, Stephen J., Nelson, George T., Slocum, Michael A., Pokharel, Nikhil, Ahrenkiel, Phil, and Hubbard, Seth M.

Subjects
*SOLAR cells, *MOLECULAR beam epitaxy, *CHARGE carrier lifetime, *PHOTOVOLTAIC power systems, *DISLOCATION density, *OPEN-circuit voltage, *EPITAXY
Abstract

GaSb grown on GaAs through interfacial misfit (IMF) arrays grown via molecular beam epitaxy has been heavily studied; there is limited research, however, on IMF growth through metal-organic vapor phase epitaxy. To demonstrate viability for integration in a multijunction solar cell for terrestrial use, it is imperative to demonstrate high quality GaSb grown on GaAs through metal-organic vapor phase epitaxy. The preferred gallium precursors for n-type and p-type GaSb for longest minority carrier diffusion length were determined to be trimethylgallium and triethylgallium, respectively. A heteroepitaxial GaSb-on-GaAs device attained an open-circuit voltage of 190 mV and an efficiency of 2.2%. Extracted threading dislocation density from the minority carrier lifetime for the heteroepitaxial GaSb-on-GaAs device was determined to be 7.5 × 10 6 cm − 2 . In a modeled multijunction solar cell, this device attributes to an overall efficiency of 33.1% under AM1.5g illumination. [ABSTRACT FROM AUTHOR]

Published
2023
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6. High figure of merit spin polarized electron sources grown via MOCVD

Author

Belfore, Benjamin, primary, Masters, Adam, additional, Poudel, Deewakar, additional, Blume, Greg, additional, Polly, Stephen, additional, Wang, Erdong, additional, Hubbard, Seth M, additional, Stutzman, Marcy, additional, Grames, Joseph Michael, additional, Poelker, Matt, additional, Grau, Matt, additional, and Marsillac, Sylvain, additional

Published
2023
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14. Toward Hot Carrier Extraction in Intervalley Photovoltaic Devices

Author

Dorman, Kyle R., primary, Whiteside, Vincent R., additional, Ferry, David K., additional, Yusuf, Israa G., additional, Legvold, Tanner J., additional, Mishima, Tetsuya D., additional, Santos, Michael B., additional, Polly, Stephen J., additional, Hubbard, Seth M., additional, and Sellers, Ian R., additional

Published
2022
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20. Advanced Power Technology Development Activities for Small Satellite Applications

Author

Piszczor, Michael F, Landis, Geoffrey A, Miller, Thomas B, Taylor, Linda M, Hernandez-Lugo, Dionne, Raffaelle, Ryne, Landi, Brian, Hubbard, Seth, Schauerman, Christopher, Ganter, Mathew, Polly, Stephen, Dann, Martin, Zhou, Xiangyang, Karkkainen, Ryan, and Roberson, Luke

Subjects
Spacecraft Propulsion And Power
Abstract

NASA Glenn Research Center (GRC) has a long history related to the development of advanced power technology for space applications. This expertise covers the breadth of energy generation (photovoltaics, thermal energy conversion, etc.), energy storage (batteries, fuel cell technology, etc.), power management and distribution, and power systems architecture and analysis. Such advanced technology is now being developed for small satellite and cubesat applications and could have a significant impact on the longevity and capabilities of these missions. A presentation during the Pre-Conference Workshop will focus on various advanced power technologies being developed and demonstrated by NASA, and their possible application within the small satellite community.

Published
2017

32. Effect of electric field on carrier escape mechanisms in quantum dot intermediate band solar cells.

Author

Yushuai Dai, Polly, Stephen J., Hellstroem, Staffan, Slocum, Michael A., Bittner, Zachary S., Forbes, David V., Roland, Paul J., Ellingson, Randy J., and Hubbard, Seth M.

Subjects
*ELECTRIC fields, *QUANTUM dots, *SOLAR cells, *LIGHT absorption, *GALLIUM arsenide
Abstract

Carrier escape and recombination from quantum dot (QD) states reduce the probability of two-step photon absorption (TSPA) by decreasing the available carrier population in the intermediate band (IB). In order to optimize the second photon absorption for future designs of quantum dot embedded intermediate band solar cells, the presented study combined the results of simulations and experiments to quantify the effect of electric field on the barrier height and the carrier escape from the QDs in InAs/GaAs quantum dot solar cells with five-layer QD superlattices. The electric field dependent effective barrier heights for ground state electrons were calculated using eight band k.p theory at short circuit conditions. With an increase in electric field surrounding the QDs from 5 kV/cm to 50 kV/cm, the effective barrier height of the ground state electrons was reduced from 147 meV to 136 meV, respectively. Thus, the increasing electric field not only exponentially enhances the ground state electron tunneling rate (effectively zero at 5 kV/cm and 7.9 × 106 s-1 at 50 kV/cm) but also doubles the thermal escape rate (2.2 × 1011 s-1 at 5 kV/cm and 4.1 × 1011 s-1 at 50 kV/cm). Temperature-dependent external quantum efficiency measurements were performed to verify that the increasing electric field decreases the effective barrier height. Additionally, the electric field dependent radiative lifetimes of the ground state were characterized with time-resolved photoluminescence experiments. This study showed that the increasing electric field extended the radiative recombination lifetime in the ground state of the QDs as a consequence of the reduced wave-function overlap between the electrons and holes. The balance of carrier escape and recombination determines the probability of TSPA. [ABSTRACT FROM AUTHOR]

Published
2017
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45. Two-step photon absorption in InP/InGaP quantum dot solar cells

Author

Kum, Hyun, primary, Dai, Yushuai, additional, Aihara, Taketo, additional, Slocum, Michael A., additional, Tayagaki, Takeshi, additional, Fedorenko, Anastasiia, additional, Polly, Stephen J., additional, Bittner, Zachary, additional, Sugaya, Takeyoshi, additional, and Hubbard, Seth M., additional

Published
2018
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49. Development of a Nano-Enabled Space Power System

Author

Polly, Stephen J., primary, Dann, Martin, additional, Fedorenko, Anastasiia, additional, Hubbard, Seth, additional, Landi, Brian, additional, Schauerman, Christopher, additional, Ganter, Matthew, additional, and Raffaelle, Ryne, additional

Published
2018
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