引入GaN过渡层对Si（111）衬底上生长GaN外延的影响

本文研究了在Si(111)衬底上生长GaN外延层的方法。相比于直接在AlN缓冲层上生长GaN外延层，引入GaN过渡层显著地提高了外延层的晶体质量并降低了外延层的裂纹密度。使用X射线双晶衍射仪、光学显微镜以及在位监测曲线分析了GaN过渡层对外延层的晶体质量以及裂纹密度的影响。实验发现，直接在AlN缓冲层上生长外延层，晶体质量较差， X射线(0002)面半高宽最优值为0.686°，引入GaN过渡层后，通过调整生长条件，控制岛的长大与合并的过程，从而控制三维生长到二维生长过渡的过程，外延层的晶体质量明显提高， (0002)面半高宽降低为0.206°,并且裂纹明显减少。研究结果证明，通过生长合适厚度的GaN过渡层，可以得到高质量、无裂纹的GaN外延层。

Impact of GaN transition layers in the growth of GaN epitaxial layer on silicon

A method for growing GaN epitaxial layer on Si (111) substrate is investigated. Due to the large lattice mismatch between GaN and AlN, GaN grown directly above an AlN buffer layer on the Si substrate turns out to be of poor quality. In this study, a GaN transition layer is grown additionally on the AlN buffer before the GaN epitaxial growth. By changing the growth conditions of the GaN transition layer, we can control the growth and merging of islands and control the transfer time from 3D to 2D growth mode. With this method, the crystalline quality of the GaN epitaxial layer can be improved and the crack density is reduced. Here, we have investigated the impact of a transition layer on the crystalline quality and stress evolution of a GaN epitaxial layer with methods of X-ray diffraction, optical microscopy and in situ reflectivity trace. With the increasing thickness of transition layer, the crack decreases and the crystalline quality is improved. But when the transition layer exceeds a critical thickness, the crystalline quality of the epilayer becomes lower and the crack density increases.