# MOCVD growth of N-polar GaN on on-axis sapphire substrate: impact of AlN nucleation layer on GaN surface hillock density

## TL;DR

This study demonstrates that optimizing the AlN nucleation layer and using indium surfactant during MOCVD growth significantly reduces surface hillock density in N-polar GaN on sapphire, without compromising crystal quality.

## Contribution

It introduces an optimized high-temperature AlN nucleation layer and indium surfactant use to substantially lower hillock density in N-polar GaN growth on sapphire.

## Key findings

- Hillock density reduced by over 80%
- Crystal quality remains high and unaffected
- Small feature density unchanged by buffer conditions

## Abstract

We report on the impact of growth conditions on surface hillock density of N-polar GaN grown on nominally on-axis (0001) sapphire substrate by metal organic chemical vapor deposition (MOCVD). Large reduction in hillock density was achieved by implementation of an optimized high temperature AlN nucleation layer and use of indium surfactant in GaN overgrowth. A reduction by more than a factor of five in hillock density from 1000 to 170 hillocks/cm$^{-2}$ was achieved as a result. Crystal quality and surface morphology of the resultant GaN films were characterized by high resolution x-ray diffraction and atomic force microscopy and found to be relatively unaffected by the buffer conditions. It is also shown that the density of smaller surface features is unaffected by AlN buffer conditions.