Heteroepitaxial Growth of Vertically-Aligned GaN Single-Crystalline Microrod Arrays on Silicon Substrates.

Abstract

The heteroepitaxial growth of vertically aligned gallium nitride (GaN) single-crystalline microrod arrays on silicon substrates was achieved with high reproducibility by using the plasma-enhanced chemical vapor deposition (PECVD) method in the furnace. By reducing the plasma power from 70 to 15 W, the crystal morphology of GaN varied from thin films to microrod arrays with the decreased V/III gas ratio. The growth of GaN crystals occurred in the vertical direction of the substrate and in the lateral direction of the growth axis via the self-catalytic vapor-liquid-solid mechanism (VLS mechanism) and the vapor-solid mechanism (VS mechanism), respectively, contributing to the formation of inverted hexagonal GaN cone microrods. Furthermore, the morphology of inverted hexagonal GaN cone microrods shows extremely small contact areas between the microrods and the substrate, suggesting the potential to solve the problems of stress accumulation and poor crystalline qualities of heteroepitaxy. With the raised growth temperature of GaN from 930 to 980 °C, the material quality was improved and the high crystalline qualities were obtained, owing to the successful surface migration of gallium atoms. However, the density of GaN microrods became lower with the increased growth temperature because the spatial temperature gradient was reduced and the evaporation of gallium was enhanced, leading to fewer gallium atoms precipitating and remaining on the substrate. The growth direction of vertically aligned GaN single-crystalline microrod arrays with the (002) crystal plane is along the [0001] orientation (c axis) and normal to the substrate surface, which may bring about many device applications in future studies.