Microscopic analysis of defects in direct synthesized GaN microcrystals

We prepared GaN microcrystals for the source material of the sublimation method by the direct reaction of Ga-melt in NH₃ ambient at temperatures of 850, 950 and 1050 °C. The typical size of the microcrystals is about 1-15 μm. The microcrystals have been investigated by solid 200 MHz nuclear magnetic resonance and micro-Raman scattering. Nuclear magnetic resonance powder spectra for ⁷¹Ga in the microcrystals were recorded near 50ppm. The disappearance of the relative broad peak in the spectra of the sample synthesized at 850 °C and the commercial GaN can be thought to come from the perturbed electric field gradient at ⁷¹Ga nuclei, which is induced by the internal stress due to native defects in the GaN microcrystals. Therefore, the GaN microcrystals synthesized at 1050 °C has the lower concentration of intrinsic defects, which is consistent with the experimental results from micro-Raman scattering measurements.