Enhanced charge recombination due to surfaces and twin defects in GaAs nanostructures

Journal Article · Sat Feb 07 00:00:00 EST 2015 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4907534· OSTI ID:22413054

Brown, Evan; Sheng, Chunyang; Nakano, Aiichiro ^[1]; Shimamura, Kohei; Shimojo, Fuyuki ^[1]

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1. Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States)

Power conversion efficiency of gallium arsenide (GaAs) nanowire (NW) solar cells is severely limited by enhanced charge recombination (CR) at sidewall surfaces, but its atomistic mechanisms are not well understood. In addition, GaAs NWs usually contain a high density of twin defects that form a twin superlattice, but its effects on CR dynamics are largely unknown. Here, quantum molecular dynamics (QMD) simulations reveal the existence of an intrinsic type-II heterostructure at the (110) GaAs surface. Nonadiabatic quantum molecular dynamics (NAQMD) simulations show that the resulting staggered band alignment causes a photoexcited electron in the bulk to rapidly transfer to the surface. We have found orders-of-magnitude enhancement of the CR rate at the surface compared with the bulk value. Furthermore, QMD and NAQMD simulations show unique surface electronic states at alternating (111)A and (111)B sidewall surfaces of a twinned [111]-oriented GaAs NW, which act as effective CR centers. The calculated large surface recombination velocity quantitatively explains recent experimental observations and provides microscopic understanding of the underlying CR processes.

• OSTI ID: 22413054
• Journal Information: Journal of Applied Physics, Vol. 117, Issue 5; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

77 NANOSCIENCE AND NANOTECHNOLOGY
COMPARATIVE EVALUATIONS
COMPUTERIZED SIMULATION
CONVERSION
EFFICIENCY
ELECTRONS
GALLIUM ARSENIDES
HETEROJUNCTIONS
MOLECULAR DYNAMICS METHOD
NANOWIRES
RECOMBINATION
SOLAR CELLS
SUPERLATTICES
SURFACES
VELOCITY