Investigation on the effect of V-type defects on the properties of GaN crystals and the formation mechanism of surface V-type defects in GaN crystals

Abstract

The influence of V-type defect formation on the properties of GaN crystals has been systematically investigated. The results indicate that the presence of V-type defects causes the destabilization and interruption of step flow on the surface of GaN crystals, which severely degrades the crystalline quality of GaN crystals. This degradation leads to a reduction in the intensity of the band-edge emission peak in the photoluminescence (PL) spectrum and the broadening of the rocking curve in high-resolution X-ray diffraction (HRXRD). Specifically, for the regions containing V-type defects, the full width at half maximum (FWHM) of the rocking curves for the (002) and (102) crystal planes increases from 58.1 arcsec and 98.8 arcsec to 101 arcsec and 139.4 arcsec, respectively. Furthermore, V-type defects alter the stress state of GaN crystals, resulting in a shift of the E₂(high) phonon mode in the Raman spectrum. In addition, the study reveals that V-type defects are highly prone to form under gallium-rich conditions. A formation mechanism of V-type defects induced by endogenous impurities is proposed. By adjusting the proportion of the gallium source atmosphere, GaN crystals free of V-type defects are successfully fabricated. This research provides theoretical guidance and technical support for the preparation of high-quality GaN crystals.