Microstructure of heteroepitaxial GaN grown on mesa-patterned 4H-SiC substrates

Cross-sectional transmission electron microscopy and atomic force microscopy have been used to study the microstructure of a thin heteroeptiaxial GaN film grown on (0001) 4H-SiC mesa surfaces with and without atomic scale steps. Analysis of a mesa that was completely free of atomic-scale surface steps prior to III–N film deposition showed that these GaN layers had a wide variation in island height (1–3μm) and included the presence of pit-like defects on the film surface. This sample had a low dislocation density (5×108∕cm2) as compared to conventionally grown samples on unpatterned (0001) on-axis 4H-SiC (2×109∕cm2), coupled with a 3–5 times increase in grain size. A comparison of a GaN film on the step-free 4H-SiC mesa region with a GaN film on a stepped 4H-SiC mesa region on the same substrate showed that the presence of surface steps reduced the overall grain size of the film from 7–10μm to a grain size of about 2–3μm. Since the GaN films grow via a Volmer–Weber mechanism, a decrease in the number of he...