Nowadays, the sputtered AlN buffer layer plays a crucial role in enhancing the crystal quality of the GaN materials. However, the ex situ buffer inevitably introduces contamination and defects, which severely decrease the performance of devices. In this work, we developed a new flow flange (FF) of GaN MOCVD to improve the process of AlN growth. Experimental results show a higher growth rate, improved radial uniformity, and enhanced crystal quality, which can be explained by the numerical calculation showing that this modification in FF leads the pyrolysis pathway of AlN’s gas-phase reaction to suppress parasitic reactions. Subsequently, by controlling the thickness of the in situ AlN buffer and its recrystallization, the morphology and orientation of nucleation islands are improved, thereby reducing the threading dislocations generated during the coalescence of the GaN film. As a result, a 6 in. GaN wafer under in situ AlN buffer with high quality and low defect is successfully grown. The threading dislocation density (TDD) is optimized to 9.37 × 107 cm–2, which is the same as that of GaN grown under ex situ AlN buffers, while the surface defect is substantially declined. Furthermore, the growth mechanism of GaN under an in situ AlN buffer using novel MOCVD is systematically concluded, supplying the high-quality materials demanded by new applications of GaN-based devices.
Wang et al. (Thu,) studied this question.