Browsing by Author "Fang, FF"

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Enhancement of Subnikov-de Haas oscillations by microwave radiation
(1997-12-01)
Fan, JC
;
Chang, YH
;
Chen, YF
;
Whang, JF
;
Fang, FF
We report for the first time that the Subnikov-de Haas (SdH) pattern can be greatly enhanced by recording the changes in the quantum oscillations of magnetoresistance due to microwave radiation. In order to understand the origin of the enhancement, the dependence of the enhanced SdH signal on temperature, microwave frequency and power has been studied. It is concluded that the enhancement can be attributed to the effects of free carrier absorption and the suppression of the nonoscillatory magnetoresistance. The technique shown here can be used to detect the SdH oscillations at relatively high temperature and in samples with moderate mobilities without perturbing the carrier concentration.
Very high hole mobility in p-type Si/SiGe modulation-doped heterostructures
(1997-03-15)
Tsai, WC
;
Chang, CY
;
Huang, GW
;
Fang, FF
;
Chang, YH
In this study, high-quality Si/Si1-xGex/Si p-type modulation-doped heterostructures were grown by ultrahigh-vacuum/chemical vapor deposition (UHV/CVD). High-field magnetotransport measurements revealed Shubnikov-de Hass oscillations in the longitudinal magneto resistance and the integer quantum Hall effect in transverse magnetoresistance illustrating the presence of a well-confined two-dimensional hole gas. The mobilities of the two-dimensional hole gas, as high as 12500 cm(2)/V . s at 0.65 K, were obtained for normal (doped layer at surface side) modulation-doped heterostructures with x = 0.12 at a sheet carrier concentration of 3.45 x 10(11) cm(-2). In addition, for this heterostructure, temperature-dependent measurements of Shubnikov-de Hass oscillations in the range 0.65 K-2.4 K were taken and the hole effective mass of 0.295m(0) + 0.01m(0) was obtained.