Effect of AlN buffer layers on the surface morphology and structural properties of N-polar GaN films grown on vicinal C-face SiC substrates

We investigated the effect of AlN buffer layers on hexagonal hillock formation and the crystallinity of N-polar GaN films grown by metalorganic chemical vapor deposition on vicinal C-face SiC substrates misoriented toward <112̄0> by 3.6 and <101̄0> by 4. As the source input group V/III ratio increased from 650 to 16310 and growth temperature was raised from 1100 C to 1150 C during AlN buffer layer growth on the substrates with <112̄0> miscut direction, the threading dislocation (TD) density of the AlN buffer layers and subsequent N-polar GaN films decreased. TD density of AlN and GaN films grown on <101̄0> misoriented substrates was higher in comparison to that grown on <112̄0> miscut substrates. The hexagonal hillock density of the N-polar GaN films was reduced by increasing the AlN V/III ratio up to 16310 and decreasing the AlN thickness from 90 to 30 nm, indicating that nucleation of inversion domain occurs during AlN buffer growth. Hexagonal hillocks were completely suppressed in N-polar GaN films grown on both substrates when the growth temperature of the 30 nm thick AlN was increased from 1100 C to 1150 C at a V/III ratio of 16310.