Conversion of 2-dimensional GaSe to 2-dimensional β-Ga2O3 by thermal oxidation

Abstract

We demonstrate the conversion to quasi two-dimensional (2D) β-Ga2O3 by thermally oxidizing layered GaSe of different thicknesses (from bilayer to 100 nm). GaSe flakes were prepared by mechanical exfoliation onto Si with a 300 nm SiO2 layer, highly oriented pyrolytic graphite (HOPG), and mica substrates. The flakes were then annealed in ambient atmosphere at different temperatures ranging from 600°C to 1000°C for 30 min. Raman spectroscopy confirmed the formation of β-Ga2O3 in the annealed samples by comparison with the Raman spectrum of a β-Ga2O3 reference crystal. Atomic force microscopy was employed to study the morphology and the thickness of the β-Ga2O3 flakes. In addition, we used energy dispersive Xray spectroscopy together with scanning electron microscopy to investigate the evolution of the composition, especially Se residuals, and the sample topography with annealing temperature. β-Ga2O3 appears at temperatures above 600°C and Se is completely evaporated at temperatures higher than 700°C. The thicknesses of the resulting β-Ga2O3 flakes are half of that of the initial GaSe flake. Here we therefore present a straightforward way to prepare 2D β-Ga2O3 by annealing 2D GaSe.