Browsing by Author "Lee, JR"

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Electrooptical properties of GaNAs/GaAs multiple quantum well structures
(2003-07-25)
Lee, JR
;
Chen, YY
;
Lu, CR
;
Lee, WI
;
Lee, SC
The electrooptical properties of the GaNAs/GaAs multiple quantum well structures have been studied using the photoreflectance spectroscopy from 20 K to room temperature. Above the band gap energy of GaAs, Franz-Keldysh oscillations were observed. The period of the Franz-Keldysh oscillations decreased slightly with decreasing temperature, and indicated that the corresponding space charge distribution varied slowly with temperature. The modulated quantum well transition features were observed below the band gap energy of GaAs. A matrix transfer algorithm was used to calculate the quantum well subband energies numerically. The band gap energy and the electron effective mass of the GaNAs/GaAs system were adjusted to obtain the subband energies to best fit the observed quantum well transition energies. (C) 2003 Elsevier Science B.V. All rights reserved.
Investigation of populated InAs/GaAs quantum dots by photoluminescence and photoreflectance
(2005-01-01)
Lee, JR
;
Lu, CR
;
Lee, WI
;
Lee, SC
;
電子物理學系
We studied self-assembled InAs/GaAs quantum dots by contrasting photoluminescence and photoreflectance spectra from 10K to room temperature. The photoluminescence spectral profiles comprise contributions from four equally separated energy levels of InAs quantum dots. The emission profiles involving ground state and excited states have different temperature evolution. Abnormal spectral narrowing occurred above 200 K. In the photoreflectance spectra, major features corresponding to the InAs wetting layer and GaAs layers were observed. Temperature dependences of spectral intensities of these spectral features indicate that they originate from different photon-induced modulation mechanisms. Considering interband transitions of quantum dots were observed in photoluminescence spectra and those of wetting layer were observed in photoreflectance profiles, we propose that quantum dot states of the system are occupied up to the fourth energy level which is below the wetting layer quantum state. (C) 2004 Elsevier B.V. All rights reserved.
Photoreflectance characterization of GaNAs/GaAs multiple quantum well structures
(2002)
Lu, CR
;
Lee, JR
;
Chen, YY
;
Lee, WI
;
Lee, SC
We investigate GaNAs/GaAs multiple quantum well structures using the photoreflectance spectroscopy at various temperatures. The modulated optical response consists of quantum well excitonic transitions and band edge transitions that exhibits Franz-Keldysh oscillatory features. The bowing parameter, effective mass, and the band-offset value were adjusted to obtain the subband energies to best fit the observed quantum well transition energies. The period of the Franz-Keldysh oscillations indicates the strength of the internal field.