The importance of nucleation layer for the GaN N-face purity on the annealed Al2O3 layers deposited by atomic layer deposition

Abstract

This study presents the results of N-face GaN layers MOCVD grown on the 20 nm thick Al2O3 layer (ALD-AlO), as a composite of a waveguiding structure. The shortening of GaN nucleation time from 195 to 60 s revealed the appearance of Ga-face inclusions in the N-face GaN, which has improved the layers’ crystal quality. It also changed surfaces’ morphology and roughness which decreased from 17 ÷ 22 nm to 5 nm. To determine the GaN face, the samples were rinsed in a KOH solution. Time-dependent etching experiment and scanning electron microscopy inspection revealed that the etching stops at the ALD-AlO layer. After 60 min of etching, we have not detected any V-pits on the surface (on the underneath Ga-face GaN), indicating etching suppression by the ALD-AlO layer. We have performed in-plane (112¯0) X-ray diffraction (XRD) measurements, atomic force microscopy (AFM) and scanning electron microscopy (SEM) imaging, electron-beam-induced-current (EBIC) investigations.