Pyramidal shape four V-grooved silicon substrate for enhancing cubic phase gallium nitride growth

Abstract

Strong spontaneous polarization and piezoelectric effects in hexagonal gallium nitride (h-GaN) seriously limit the efficiency of h-GaN-based devices. To overcome this issue, a pyramidal-shaped four V-grooved silicon (4PVG-Si) patterned substrate is introduced for transforming h-GaN into cubic GaN (c-GaN) at the nanoscale. The purpose of using 4PVG-Si instead of simple V-grooved Si (VG-Si) is to improve the crystal quality with the maximum cubic volume of GaN. The growth of c-GaN was verified by high-resolution x-ray diffraction and cathodoluminescence, whereas high-resolution transmission electron microscopy (HRTEM) was further used to analyze the excessive and smooth c-GaN growth. The HRTEM images revealed that optimizing the growth of an aluminum nitride layer with 10–15 nm thicknesses promotes the maximum c-GaN volume. However, exceeding this thickness tended to the reduction in c-GaN volume, resulting in the development of big voids with abnormal tip-shaped growth. In the presence of big voids and abnormal tip-shaped growth, the hexagonal growth closed very late, and the cubic volume of c-GaN is reduced. To further promote the cubic phase of GaN, the growth conditions of GaN were also optimized. Our results proved that the design of 4PVG-Si and optimized growth conditions promote the maximum cubic volume of GaN.