中文摘要：

采用MOCVD技术在r面蓝宝石衬底上采用两步AlN缓冲层法外延制备了a面GaN薄膜.利用高分辨X射线衍射技术和Raman散射技术分析了样品的质量以及外延膜中的残余应力.实验结果表明：样品的（11-↑20）面的X射线双晶摇摆曲线的半峰宽仅为0.193°，Raman光谱中E2高频模的半峰宽仅为3.9cm^-1，这些说明a面GaN薄膜具有较好的晶体质量；X射线研究结果表明样品与衬底的位相关系为：[11-↑20]GaN‖[1-↑102]sapphire，[0001]GaN‖[-↑1101]sapphire和[-↑1100]GaN‖[11-↑20]sapphire；高分辨X射线和Raman散射谱的残余应力研究表明，采用两步AlN缓冲层法制备的a面GaN薄膜在平面内的残余应力大小与用低温GaN缓冲层法制备的a面GaN薄膜不同，我们认为这是由引入AlN带来的晶格失配和热失配的变化引起的.

英文摘要：

a-plane GaN films were grown on r-plane sapphire substrates by metalorganic chemical vapor deposition with a two-step AlN buffer layer. High-resolution X-ray diffraction and micro-Raman scattering were used to analyze the residual strain and crystalline quality of the as-grown samples. The on-axis full width at half maximum value （FWHM） of the X-ray rocking curve is 0. 193°,and the FWHM of the E2-high energy peak is 3. 9cm^-1,indicating that the as-grown sample is of high quality. The orientation of the a-plane GaN with respect to r-plane sapphire substrate is confirmed to be [11-↑20]GaN ｜｜ [1-↑102]sapphire, [0001]GaN ｜｜[-↑1101]sapphire and [-↑1100]GaN ｜｜ [11-↑20]sapphire. The residual stress of the a-plane GaN grown with two- step AlN buffer is different from that of the a-plane GaN grown with a low-temperature GaN buffer,due to the effects of the AlN buffer,which has a larger thermal mismatch to sapphire than that of GaN.