Crystalline orientation and anisotropy of semi-polar GaN films grown on m-sapphire substrate by hydride vapor phase epitaxy

Abstract

In this paper, semi-polar (10–13) and (11–22) GaN layers were fabricated on m-plane sapphire templates by vertical hydride vapor phase epitaxy system. The GaN layer with a thickness of 10 μm, excluding the thickness of the template. By systematically optimized growth parameters, high quality semi-polar layers were achieved and confirmed by high resolution X-ray diffraction (HR-XRD) measurement, with a rocking curve width of 0.15° for (10–13) GaN layer and 0.31° for (11–22) GaN layer. In-plane epitaxial relationships between (10–13) or (11–22) GaN and sapphire substrates were also determined by HR-XRD. Crystalline anisotropies were shown in two aspects. One is associated with the crystal quality, which can be measured by the full width at half maximum (FWHM) value curves on azimuth Phi angles and originated from the different atom mobility along different crystal directions on growing surface. The other one is associated with defects on the surface, which can be clearly recorded by optical cameras. When defects of epitaxial films accumulate, the shape of FWHM curves dependence on Phi degree changed from M−type to W-type. These two kinds of anisotropic features are closely connected with each other.