Conversion of 2-dimensional GaSe to 2-dimensionalβ-Ga₂O₃by thermal oxidation

We demonstrate the conversion to quasi two-dimensional (2D)β-Ga₂O₃by 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 SiO₂layer, highly oriented pyrolytic graphite, 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 ofβ-Ga₂O₃in the annealed samples by comparison with the Raman spectrum of aβ-Ga₂O₃reference crystal. Atomic force microscopy was employed to study the morphology and the thickness of theβ-Ga₂O₃flakes. In addition, we used energy dispersive x-ray spectroscopy together with scanning electron microscopy to investigate the evolution of the composition, especially Se residuals, and the sample topography with annealing temperature.β-Ga₂O₃appears at temperatures above 600 °C and Se is completely evaporated at temperatures higher than 700 °C. The thicknesses of the resultingβ-Ga₂O₃flakes are half of that of the initial GaSe flake. Here we therefore present a straightforward way to prepare 2Dβ-Ga₂O₃by annealing 2D GaSe.