Energy Relaxation And Diffusion Of Photoexcited Carriers In Symmetric And Asymmetric GaAs Quantum Wells

Kai Shum; Mahesh R. Junnarkar; Hsieh Shin Chao; R. R. Alfano; H. Morkoc

doi:10.1117/12.940857

3 August 1987 Energy Relaxation And Diffusion Of Photoexcited Carriers In Symmetric And Asymmetric GaAs Quantum Wells

Kai Shum, Mahesh R. Junnarkar, Hsieh Shin Chao, R. R. Alfano, H. Morkoc

Proceedings Volume 0793, Ultrafast Laser Probe Phenomena in Bulk and Microstructure Semiconductors; (1987) https://doi.org/10.1117/12.940857
Event: Advances in Semiconductors and Semiconductor Structures, 1987, Bay Point, FL, United States

Abstract

Subpicosecond time-resolved photoluminescence studies of a symmetric multiple quantum well structure and an asymmetric quantum well with a similar well thickness have revealed several important experimental results on the behavior of photoexcited carriers in these microstructures: (1) The energy relaxation process is substantially suppressed due to the existence of a large population of nonequilibrium phonons after an initial rapid cooling. (2) The two different well structures do not show any difference in the energy relaxation process under the same experimental conditions. (3) The photoexcited carrier density deduced from exact and consistent fittings of the time-resolved photoluminescence profiles at various emitted photon energies decreases nonexponentially and very rapidly within the first 30 ps after the end of a 0.5 ps pulse. An effective carrier depletion time is determined to be as short as 10 ps in either well. A mechanism which leads to such short carrier depletion time is found to be associated with the nonequilibrium phonon enhanced phonon replica emission. Unlike conventional stimulated emission behavior, this mechanism is even more effective in exhausting carriers from the system at higher temperatures. (4) The difference in potential well profile corresponds to a very different behavior of carrier diffusion process in the lateral well plane. The carrier diffusion is enhanced in the well plane of the asymmetric well by restricting carrier diffusion in the growth direction. Diffusivity D of the photoexcited carriers in the asymmetric well has been directly determined to be 106cm2/s at 4.3K, which is about four orders of magnitude larger than the value in bulk GaAs.

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Kai Shum, Mahesh R. Junnarkar, Hsieh Shin Chao, R. R. Alfano, and H. Morkoc "Energy Relaxation And Diffusion Of Photoexcited Carriers In Symmetric And Asymmetric GaAs Quantum Wells", Proc. SPIE 0793, Ultrafast Laser Probe Phenomena in Bulk and Microstructure Semiconductors, (3 August 1987); https://doi.org/10.1117/12.940857

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KEYWORDS

Luminescence

Phonons

Electrons

Picosecond phenomena

Diffusion

Quantum wells

Gallium arsenide

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