| Summary: | This thesis focuses on the growth of high quality III-nitride materials by MOCVD along both c-direction and non-polar a-direction. High temperature AlN buffer layer is introduced, which can effectively reduce the dislocation density of the overlying layer. Stimulated emission at 340nm has been obtained by such AlN buffer techniques, which mechanism is understood by studying the strain relaxation in the QW structure with RSM measurements. A non-polar overgrowth approach has also been established for the growth of non-polar GaN, leading to an impressive improvement in the crystalline quality. Meanwhile, optical investigation on c-plane InGaN/GaN MQW nanorod structures has been performed, demonstrating an significantly enhanced photoluminescence emission. It has been concluded that the enhancement is due to the reduction on quantum confined Stark effect caused by strain relaxation in the MQW structure.
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