Browsing by Author "Tsai, KL"

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Compositional disordering of InGaAs/GaAs heterostructures by low-temperature-grown GaAs layers
(1996-01-15)
Tsang, JS
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Lee, CP
;
Lee, SH
;
Tsai, KL
;
Tsai, CM
Compositional disordering of InGaAs/GaAs superlattices using a low-temperature-grown GaAs cap layer (LT-GaAs) by molecular beam epitaxy has been studied. The disordering of the superlattice was verified by photoluminescence and double-crystal x-ray rocking curve measurements. The Ga-vacancy-enhanced interdiffusion due to the presence of LT-GaAs was found to be the disordering mechanism. Diffusion equations and the Schrodinger's equation were solved numerically to obtain the composition profile and the transition energies in the disordered quantum well, respectively. The simulated energy shifts for samples under different annealing conditions agreed very well with the experimental results. The calculated effective diffusivity for the In-Ga interdiffusion has an activation energy of 1.63 eV, which is smaller than the activation energy 1.93 eV, for intrinsic interdiffusion. The diffusivity for the enhanced In-Ga interdiffusion due to the presence of LT-GaAs is about two orders of magnitude larger than the intrinsic In-Ga diffusivity. (C) 1996 American Institute of Physics.
The effect of barrier structure on the performance of double barrier quantum well infra-red photodetectors
(1996-02-01)
Tsai, KL
;
Lee, CP
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Chen, PC
;
Tsang, JS
;
Tsai, CM
The effects of the inner and outer barriers on the performance of mid-wavelength (3-5 mu m) GaAs/AlGaAs double barrier quantum well infra-red photodetectors (DBQWIPs) have been studied. It was found that the peak response wavelength had a significant red shift when the thickness of the AlAs inner barriers was below 10 Angstrom. This is attributed to the lowering of the upper state energy in the quantum wells. The responsivity of DBQWIPs decreases with the inner barrier thickness. This is because the optical gain decreases faster than the increasing rate of the quantum efficiency when the inner barrier thickness increases. The responsivities for devices with different Al compositions (0.35 and 0.24) in the outer barriers are in the same range, but the dark currents for devices with Al(0.35)G(0.65)As outer barriers are much lower than those with Al0.24Ga0.76As outer barriers. Nearly two orders of magnitude improvement in detectivity was observed when the Al composition in the outer barriers was changed from 0.24 to 0.35. A high detectivity of 1 x 10(11) cm Hz(1/2) W-1 at 77 K was obtained for a device with 12 Angstrom AlAs inner barriers and 300 Angstrom Al0.35Ga0.65As outer barriers.