Impacts of specific element-treated three-dimensional GaN layer on characteristics of nonpolar a-plane GaN film

Nonpolar a-plane GaN films with three-dimensional (3D) GaN layers have successfully grown on r-plane sapphire substrates by metal organic chemical vapor deposition. The inserted 3D GaN layers were grown accompanied with the treatment by various kinds of elements such as Si, Mg, and In to further improve the characteristics of the subsequently lateral overgrown nonpolar a-plane GaN films. Scanning electron microscopy, x-ray rocking curve, and room temperature photoluminescence spectroscopy were used to examine the effects of the introduction of the specific element-treated 3D GaN layer on the crystalline quality, the anisotropy, and the optical property of the nonpolar a-plane GaN film. It was found that significant improvements in the crystalline quality and optical property as well as a remarkable reduction in anisotropy have been achieved for the nonpolar a-plane GaN film grown on the r-plane sapphire substrate by inserting a 3D GaN layer treated with Si. In fact, evident reduction in full width at half maximum of x-ray rocking curves from 972 to 651 arcsec along the c-axis (φ = 0°) and from 1234 to 752 arcsec along the m-axis (φ = 90°), and a notable decrease in anisotropy from 27.0% to 15.6% were obtained with the employment of Si treatment to the 3D GaN layer.