| Summary: | 碩士 === 國立臺灣大學 === 物理研究所 === 93 === Hall effect and Shubnikov-de Haas (SdH) effect measurements are two most frequently used tools for characterizing the electronic transport properties in a semiconductor. This dissertation consists of the following two parts, regarding these two techeniques respectively.
1.Electron transport in InN films
We have preformed the electric transport measurements on InN films overa wide temperature range. Our results show that, within the experimental error, the carrier density are temperature-independent, similar to that in a metal. Such results indicate that we can consider our InN films as degenerate electron systems in which the Fermi level is much higher than the conduction band over the whole measurement range. Moreover, our results suggest that over a wide temperature range the dominant scattering mechanism is residue imperfection scattering since ρRT is only 10% more than ρ4k. That tells us in InN films it is the residue impurity scattering limits the electronic transport. So in order to obtain higher-mobility InN system, one needs to substantially reduce the number of background impurities and defects during the growth. Our data demonstrate that electron transport in InN is metallic-like, which is further supported by the observation that temperature dependence of the acoustic-phonon mobility shows a T-5 dependence.
2.Microwave-modulated transport in a GaAs/AlGaAs electron system :
Measurements of microwave-modulated SdH-like oscillation were carried out in a GaAs/AlGaAs heterostructure. The microwave-modulation technique is used to enhance the visibility of the oscillatory pattern while keeping the carrier density constant, and I performed some further measurements in order to figure out the exact electron temperature when the sample is under microwave illumination. By comparing the SdH oscillations under continuous microwave with different power and SdH oscillations at different temperature, our results show that the electron temperature increase is very small, less than 0.3 K. Besides, the spin-splitting phenomenon under chopped microwave is also observed, and the oscillatory pattern is asymmetric. At present, we have not found a plausible explanation of it.
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