Comparative Investigation of Semipolar (11-22) GaN Layers on m-Plane Sapphire with Different Nucleation Layers

We present the growth of semipolar (11-22) GaN layers on m-plane sapphire by low pressure metal organic chemical deposition. The influence of nucleation layer was studied on the crystal quality of GaN epilayers which exhibited an obvious in-plan anisotropic mosaicity with the symmetric on-axis (11-22) plane reflection and asymmetric off-axis plane refection X-ray diffraction (XRD) measurement. It is shown that the XRD full width at half maximum (FWHM) values for the GaN epilayers are narrowed closer to the ~310 arc seconds along the GaN c-axis projected direction ([-1-123]). It was found that the growth process played an important role in the reduction of the FWHM values, but did not have noticeable change to the surface roughness of GaN epilayers. The variable temperature photoluminescence measurements of GaN layer show the broad emission spectra. The silent Raman modes around 310 cm⁻¹ and 330 to 331 cm⁻¹ are found in Raman measurements.