Interfacial effects during GaN growth on 6H-SiC

Abstract

GaN growth on 6H-SiC was investigated for heterojunction device applications. Dopant diffusion and surface reactions were discovered at the GaN/SiC heterojunction. A systematic study was therefore conducted focusing on: 1) SiC substrate preparation, 2) SiC nitridation; the effect of flowing ammonia (NH₃) at 1050°C on the SiC, and 3) the conductivity type and carrier concentration of the SiC substrate. Atomic force microscopy measurements revealed that the SiC substrates became smoother after the nitridation process possibly due to nitrogen chemisorption and etching. Current-voltage and capacitance-voltage measurements on Cr-Schottky diodes made on SiC revealed evidence for an increased potential barrier in the nitrided samples that can be explained by an interfacial monolayer ofSiN_x. Furthermore, we compared GaN/SiC heterojunction n-n and n-p diodes made from direct and selective GaN growth. Capacitancevoltage measurements on GaN/SiC n-p heterojunctions indicate that the effective doping in the junction increases as the growth temperature increases. Secondary ion mass spectrometry measurements exposed a tail of Al in the GaN due to acceptor out-diffusion from the p-SiC.