Browsing by Author "Chu, AK"

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Determination of built-in field by applying fast Fourier transform to the photoreflectance of surface-intrinsic n(+)-type doped GaAs
(1999-01-18)
Wang, DP
;
Wang, KR
;
Huang, KF
;
Huang, TC
;
Chu, AK
Photoreflectance spectroscopy of surface-intrinsic n(+)-doped (s-i-n(+)) GaAs has been measured at various power densities (P-pu) of a pump beam. Many Franz-Keldysh oscillations (FKOs) were observed above the band-gap energy, which will enable the electric-field strength (F) to be determined from the periods of the FKOs. Field F thus obtained is subject to photovoltaic effects. In order to reduce the photovoltaic effects from the pump beam, P-pu was kept below 10 mu W/cm(2) in the previous experiments. Here, we demonstrate that the built-in field can be determined at a larger P-pu by using fast Fourier transform techniques. (C) 1999 American Institute of Physics. [S0003-6951(99)02803-X].
Effect of modulating field on photoreflectance simulated by electroreflectance
(1999-04-01)
Chiou, SJ
;
Sung, YG
;
Wang, DP
;
Huang, KF
;
Huang, TC
Photoreflectance (PR) of surface-intrinsic- n(+) (s-i-n(+)) type doped GaAs has been simulated by electroreflectance (ER). The simulated spectra of the s-i-n(+) sample have exhibited many Franz-Keldysh oscillations, which enable the electric field (F) to be determined. It is known that F's determined from PR are subjected to photovoltaic effect and the measured F is close to F-bi -delta F/2 when the modulating field, delta F much less than F-bi, where F-bi is the built- in field of the sample and delta F is the modulating field. In this work, we have investigated the relation between the measured F and delta F not only for the region where delta F much less than F bi holds, but also for a whole range of delta F. In order to determine the magnitude of dF, we have used ER to simulate PR, that is, the measurements of ER under a forward bias, which is set to be equal to delta F/2. (C) 1999 American Institute of Physics. [S0021-8979(99)01906-4].
Temperature dependence of Fermi level obtained by electroreflectance spectroscopy of undoped n(+)-type doped GaAs
(1997-12-29)
Huang, KM
;
Wang, KL
;
Wang, DP
;
Huang, KF
;
Huang, TC
The electroreflectance (ER) spectra of an undoped n(+)-type doped GaAs have been measured over a range of temperature from 25 to 400 K. Many Franz-Keldysh oscillations were observed above the band-gap energy, which enabled the electric field strength and, hence, also the Fermi level to be determined. The photovoltaic effect is shown to be negligible, even at the low temperature. The experiment shows that the Fermi level decreases with increasing temperature and has almost the same temperature dependence as the energy gap. It is pinned at about 0.63 of energy gap below the conduction band. (C) 1997 American Institute of Physics.