α-Ga2O3 grown by low temperature atomic layer deposition on sapphire

alpha-Ga2O3 is a metastable phase of Ga2O3 of interest for wide bandgap engineering since it is isostructural with alpha-In2O3 and alpha-Al2O3. alpha-Ga2O3 is generally synthesised under high pressure (several GPa) or relatively high temperature (similar to 500 degrees C). In this study, we report the growth of alpha-Ga2O3 by low temperature atomic layer deposition (ALD) on sapphire substrate. The film was grown at a rate of 0.48 angstrom/cycle, and predominantly consists of alpha-Ga2O3 in the form of (0001)-oriented columns originating from the interface with the substrate. Some inclusions were also present, typically at the tips of the alpha phase columns and most likely comprising epsilon-Ga2O3. The remainder of the Ga2O3 film - i.e. nearer the surface and between the alpha-Ga2O3 columns, was amorphous. The film was found to be highly resistive, as is expected for undoped material. This study demonstrates that alpha-Ga2O3 films can be grown by low temperature ALD and suggests the possibility of a new range of ultraviolet optoelectronic and power devices grown by ALD. The study also shows that scanning electron diffraction is a powerful technique to identify the different polymorphs of Ga2O3 present in multiphase samples. (C) 2018 Elsevier B.V. All rights reserved.