| Summary: | 碩士 === 國立交通大學 === 應用化學系所 === 97 === In this thesis, we used optical techniques to investigate semiconductor low-dimensional structures. The thesis was composed of two parts:
In the first part, we investigated optical properties of zero-dimensional nanostructure. We compared results of quantum dots (QDs) with quantum rings (QRs) by measuring photoluminescence excitation (PLE) and activation energy (Ea).In the PLE spectrum, we observed different behavior between dots and rings. The two different results were ascribed to the position of discrete state in the QDs and QRs, which leads to two distinct relaxation mechanisms for the carriers in the QDs and QRs. We could obtain the Ea in the QDs and QRs were retrieved from the temperature dependent PL spectra. Although the Ea of the QRs is smaller, however, the dark state in the QRs provide an escaping channel for the photoexcited carriers. Therefore, the luminescence efficiency is better in the QRs at high temperature.
In the second part, we used time correlated single photon counting technique to investigate the PL lifetime in cobalt doped zinc oxide (ZnO) at various temperatures. We observed the different behaviors of carrier relaxation between ZnO defect and d-d transition .An energy level model was proposed to explain our experimental results.
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