Phase and morphological transformations of GaS single crystal surface by thermal treatment

GaS single crystal layers have been thermally treated under argon flow for 4 h at two different temperatures (700 °C and 900 °C). The starting GaS sample and the annealed ones have been characterized by X- ray diffraction, Raman spectroscopy, scanning and transmission electron microscopy. It was found that GaS transformed into β-Ga2O3 through the formation of Ga2S3 intermediate phase. Moreover, such an oxidation process involved the growth of dense Ga2S3 sub-micron crystallites at a temperature of 700 °C and relatively long β-Ga2O3 nanowires (up to 4 μm) at a temperature of 900 °C. Experiments also evidenced that an intentional supply of oxygen was unfavourable both to the formation of Ga2S3 phase and to the growth of sub-micron crystallites and nanowires.