| Summary: | 碩士 === 國立臺灣大學 === 物理研究所 === 95 === This work is composed of two parts including measurements associated with magnetotransport of two-dimensional electron gas (2DEG) in semiconductor heterostructures, which provides substantial information on the transport phenomena in heterostructures.
We reported the photoconductivity of two-dimensional electron gas (2DEG) in GaAs/AlGaAs heterostructure. The signal we observed was the magnetoresistivity under the microwave illumination (12dBm; 20GHz~30GHz). Comparing with the results of the standard magnetoresistivity measurements we found that the effect induced by continuous microwave could be possibly due to hot carrier effect. However, by means of modulated-microwave technique we could directly detect the effect induced by the microwave. Therefore, the measurements concern microwave frequency, microwave power, magnitude of current source, and temperature dependence of the microwave modulated signal were performed. The results show that the peaks of the magnetoresistivity oscillations shift as the microwave frequency is changing. Nevertheless, we were still able to observe microwave modulated signals while the current source was turn off. These signals associated with photovoltaic effect had been studied further by understanding the microwave frequency and temperature dependence of them.
We also reported on magnetotransport results of "AlGaN/GaN" high electron mobility transistor structure grown on p-type Si (111) substrate. The results show that there exists an approximately temperature (T)-independent point in the longitudinal resistivity ρ_XX which could be ascribed to a direct transition from a weak insulator to a high Landau level filling factor quantum Hall state at low magnetic fields. And the Hall resistivity decreases with increasing T, compelling experimental evidence for electron-electron interaction effects in a weakly disordered system. However, quantum correction has attracted much attention recently because of the theory of Zala et al. In order to verify these new theories, we would used them to analyze the experimental results.
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