Improvements of epitaxial quality and stress state of GaN grown on SiC by in situ SiNx interlayer

In this study, 4.5 μm thick GaN films with graded Al_xGa_1?xN/AlN buffer and SiN_x interlayer were prepared on 6H–SiC substrates by metal–organic chemical vapor deposition. To determine the effects of SiN_x interlayer on epitaxial quality and stress state of GaN films, a series of comparative experiments were carried out by changing the deposition time and the insert location of SiN_x interlayer. By optimizing growth conditions of SiN_x interlayer, the full width at half maximum values of ( (0002) ) and ( (10bar{1}2) ) rocking curves of GaN films were improved to 142 and 170 arcsec, respectively. A crack-free GaN film with a small root-mean-squared roughness of 0.21 ± 0.02 nm was achieved. Simultaneously, the reduction in threading dislocation density of GaN films was confirmed by using wet etching method. In addition, stress values in GaN films were investigated by Raman and low-temperature photoluminescence spectra, which indicated that the lower tensile stress in GaN film, the higher the film’s crystallinity.