The Effect of AlN Nucleation Temperature on the Growth of AlN Films via Metalorganic Chemical Vapor Deposition

Abstract

AlN epilayers were grown directly on sapphire (0001) substrates using a combined growth scheme, consisting of a low-temperature nucleation layer and a second layer grown by high-temperature pulsed atomic layer epitaxy via metalorganic chemical vapor deposition. With an emphasis on the nucleation layer, its growth temperature was varied from 470°C to 870°C, and obvious differences in the surface morphology, crystal quality, and strain states of the overall AlN epilayers were observed. Based on atomic force microscopy, x-ray diffraction, and Raman spectroscopy results, these differences are ascribed to the nucleation sites and the subsequent grain size. Due to the enhanced mobility of Al adatoms with increasing temperature, the nucleation sites decrease and the subsequent grain size increases, leading to the achievement of atomically flat AlN epilayers with good crystal quality for the nucleation layer grown at 570°C. However, at higher nucleation layer growth temperature, the properties of the AlN epilayers deteriorate due to the possible appearance of misaligned AlN grains. A model is also developed according to all observations.