Browsing by Author "Song, TS"

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Carrier-carrier scattering in GaAs/AlxGa1-xAs quantum wells
(2000-06-15)
Sun, KW
;
Song, TS
;
Sun, CK
;
Wang, JC
;
Kane, MG
We have studied carrier dynamics in highly nonequilibrium two-dimensional (2D) carrier distributions generated with femtosecond laser pulses in p-doped GaAs/Al0.32Ga0.68As quantum wells at photoexcited carrier densities between 10(9) and 10(11) cm(-2). The initially nonthermal carrier distribution is quickly broadened due to inelastic carrier-carrier scattering, with the broadening rate increasing as carrier density is increased. Measurements of the unrelaxed peak height in the hot electron-neutral acceptor luminescence spectra are compared with calculations of the carrier distribution using integration of the 2D dynamically screened Boltzmann equation. Our results indicate that carrier-carrier scattering becomes as significant a scattering mechanism as LO-phonon emission at density of about 10(10) cm(-2).
Nonthermal carrier dynamics in AlxGa1-xAs/GaAs quantum wells
(2000-05-01)
Sun, KW
;
Song, TS
;
Wang, SY
;
Lee, CP
;
電子工程學系及電子研究所
We present new time-resolved measurements that demonstrate the effect of injected carrier densities on carrier-carrier scattering rates of highly nonequilibrium carrier distributions in the p-doped Al0.32Ga0.68As/GaAs quantum wells with well width of 5 and 3 nm. The spectra at high densities (greater than or equal to 10(10) cm(-2)) demonstrate that the initially narrow electron distribution is altered in a time less than or equal to the LO phonon emission time as the result of rapid carrier-carrier scattering. At about the same excitation density (similar to 10(10) cm(-2)), the carrier-carrier scattering rate is faster in 3 nm quantum wells in comparison to 5 nm wells. Our results also indicate that carrier-carrier scattering becomes as significant as LO phonon emission at density of about 1 X 10(10) cm(-2) in the 5 nm quantum wells. (C) 2000 Elsevier Science B.V. All rights reserved.
Raman and hot electron-neutral acceptor luminescence studies of electron-optical phonon interactions in GaAs/AlxGa1-xAs quantum wells
(2000)
Sun, KW
;
Chang, HY
;
Wang, CM
;
Song, TS
;
Wang, SY
Using two optical techniques, we have studied the hot electron-optical phonon interactions in GaAs/AlxGa1-xAs multiple-quantum wells. Raman scattering measurements at 15 K are presented for the Al composition of x = 0.3, 0.5, 0.7 and 1.0. The GaAs-like and AlAs-like phonon frequencies of the first-order modes are also measured as a function of Al composition. The optical phonon energies emitted by the photoexcited electrons in quantum wells are determined by using hot electron-neutral acceptor luminescence techniques. It is shown that the relaxation of hot electrons in the quantum wells is dominated by the GaAs LO phonon emission for small x, but by AlAs-like LO phonons for larger Al composition. (C) 2000 Elsevier Science Ltd. All rights reserved.
Ultrafast carrier-carrier scattering in AlxGa1-xAs/GaAs quantum wells
(1999-12-01)
Sun, KW
;
Song, TS
;
Sun, CK
;
Wang, JC
;
Wang, SY
We present new time-resolved measurements that demonstrate the effect of injected carrier densities on carrier-carrier scattering rates of a highly nonequilibrium carrier distribution in the p-doped Al0.32Ga0.68As/GaAs quantum wells. The initially photoexcited nonthermal carrier distribution is quickly broadened due to rapid increase of the inelastic carrier-carrier scattering as the injected carrier densities increased toward 10(11) cm(-2). (C) 1999 Elsevier Science B.V. All rights reserved.