| Summary: | 碩士 === 國立臺灣大學 === 物理研究所 === 92 === This dissertation describe the measurements on the electron transport in two-dimensional GaAs/AlGaAs electron systems and optical properties of InGaAsN/GaAs single quantum well with different nitrogen content. This dissertation consists of the following three parts.
1. Peak values of resistivity in a high-mobility GaAs/AlGaAs electron system
We presented magneto transport measurements on a high-quality GaAs electron system. We found that the peak values of resistivity increase linearly with magnetic field and break down when spin splitting becomes resolved. This interesting phenomena can be well interpreted by the quantum diffusion model and Coleridge argued that we can estimate quantum lifetime using this model. In addition, we also observed quantum lifetime has the same temperature dependence on Shubnikov-de Hass (SdH) theory and quantum diffusion model, it implies SdH theory and quantum diffusion model need to be modified for my sample. We speculate this modification may be due to thermal broadening.
2. Upshift of the fractional quantum Hall plateaus
It is now established that if there are an equal number of positively and negatively charged impurities, the quantum Hall plateaus in �漚y(B) are expected to be centred about the classical value �漚y = B/(en) where n is the 2D carrier density. It has also been shown that when repulsive or attractive scattering centres are deliberately introduced close to a two-dimensional electron gas (2DEG), the centres of the quantum Hall plateaus are shifted to higher or lower magnetic field, respectively. We extend this concept to the composite fermions where each electron is bound to two magnetic flux quanta. By studying the upshift of the ��=1 quantum Hall plateau, We provide compelling evidence that the dominant scattering for the composite fermions is different from that for electrons.
3. Optical properties of InGaAsN/GaAs single quantum well with different nitrogen content
In this part, we report the PL studies of InGaAsN/GaAs single quantum well (SQW) with various nitrogen content. The bandgap reduction of InGaAsN has been found with increasing nitrogen content. In addition, the PL properties have been investigated for various excitation intensities and temperatures when nitrogen is added. It was observed that the PL peak energy increases with excitation power like exponential relation at low temperature. The PL peak energy exhibits S-shape dependence while the FWHM exhibits N-shape dependence with temperature. All observed results can be well explained by localization effect due to the local fluctuations of nitrogen composition.
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