| Summary: | 碩士 === 國立高雄大學 === 應用物理學系碩士班 === 99 === This study is to investigate the anisotropic characteristics of nonpolar a-plane InGaN/GaN multiple quantum wells (MQWs) and semipolar (11-22) InGaN/GaN MQWs. The characteristics of the samples are measured by using temperature-dependence photoluminescence (PL), and time-resolved photoluminescence (TRPL) measurements, atomic force microscopy (AFM), field-emission electron microscopy (FE-SEM), and cathodoluminescence (CL).
For nonpolar a-plane InxGa1-xN/GaN MQW samples, the sample shows a rougher surface morphology in the high-indium-content samples. Two main emission bands PH and PL in PL attributed to MQWs-related and localized states were observed, respectively. As the indium content increases, the sample shows a lower degree of polarization. Also, the lifetime of high energy emission peak depends on the polarization, while that of the low energy emission peak is not sensitive to the polarization.
For the semi-polar (11-22) InGaN/GaN MQWs grown on HT-AlN (InGaN/GaN/HT-AlN sample) and LT-GaN (InGaN/GaN/LT-GaN sample) buffer layers, the InGaN/GaN/LT-GaN MQW sample has a striation feature with a larger roughness. The obvious feature and larger roughness were characterized by higher densities of SFs. In addition, two main emission bands in PL attributed to GaN- and MQWs-related were observed. It was found that the degree of polarization of InGaN/GaN/HT-AlN MQW sample is higher than that of InGaN/GaN/LT-GaN MQW sample. Also, from the TRPL results, the longer lifetimes of InGaN/GaN/LT-GaN MQW sample suggests that poor quantum well structures delay carrier relaxation.
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