The influence of substrate etched on the quality of GaN epilayers

► Sapphire substrate is etched by H3PO4 and NaOH. ► The Raman scattering spectroscopy and photoetching analyses show that the substrate etched can effectively decrease the residual stress and the dislocations density in these epilayers. ► The X-ray diffraction analysis shows the process can reduce the value of the FWHM.