Study of lateral growth regions in ammonothermal c-plane GaN

Lateral growth in the a-direction is an effective way to expand the size of crystal in basic ammonothermal GaN growth. Cathodoluminescence image of cross section clearly revealed several different regions along a-direction. Stress distributions and optical properties were investigated among these different regions by Raman spectroscopy and photoluminescence spectroscopy, respectively. TOF-SIMS mapping showed the spatial distribution of O, H, Si and C impurities in lateral growth regions. Our results indicate that there is small stress variation among the interfaces. Different concentration of impurities incorporated in these regions, especially O impurity, which can significantly increase the free carrier concentration. Fairly low concentration and uniform distribution of C impurity indicated that YL band in PL spectra is not closely related to carbon impurity or a complex involving carbon. Based on the above data, the evolution process of lateral crystal growth is deduced.