Growth and Stress Analysis of a-Plane GaN Films Grown on r-Plane Sapphire Substrate with a Two-Step AlN Buffer Layer

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 ［1120］GaN‖［1102］sapphire,［0001］GaN‖[1101］sapphire and ［1100］GaN‖［1120］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.