Evolution of morphology and crystalline quality of DC-sputtered AlN films with high-temperature annealing

Abstract

High-temperature annealing (HTA) is a promising technique to improve the crystalline quality of AlN films. Combining HTA with RF sputtering, Miyake et al. have reported the fabrication of high-quality AlN templates on sapphire [J. Cryst. Growth 456, 155 (2016)], which paves the way to realizing low-cost AlGaN UV optical devices. In terms of AlN growth, DC sputtering is interesting because of its low cost and high throughput. We studied the effect of HTA on the morphology and crystalline quality of DC-sputtered AlN films. As with RF sputtering, HTA substantially improved the crystalline quality of DC-sputtered AlN films. In contrast, hillocks were formed on the surface after HTA, which plausibly stems from the rough surface with spiked structures of the DC-sputtered film. Additional growth of AlN on annealed samples improved the surface morphology and crystalline quality except for the sample containing large hillocks.