Hydrogen Adsorption on Ga2O3 Surface: A Combined Experimental and Computational Study

In the present work, hydrogen adsorption on the Ga2O3 surfaces was investigated using Fourier transform infrared spectroscopy (FTIR) measurements and periodic density functional theory (DFT) calculations. Both the FTIR and DFT studies suggest that H-2 dissociates on the Ga2O3 surfaces, producing OH and GaH species. The FTIR bands at 3730, 3700, 3630, and 3600 cm(-1) are attributed to the vibration of the OH species whereas those at 2070 and 1990 cm(-1) to the GaH species. The structures of the species detected in experiments are established through a comparison with the DFT calculated stretching frequencies. The O atom of the experimentally detected OH species is believed to originate from the three-coordinated surface O atom. However, the H adatom that binds the coordinately unsaturated Ga atom results in the experimentally detected GaH species. Dissociative adsorption of H-2 on the perfect Ga2O3 surface, with the formation of both OH and GaH species, is endothermic and has an energy barrier of 0.90 eV. In contrast, dissociative adsorption of H-2 on the defective Ga2O3 surface with oxygen vacancies, which mainly produces GaH species, is exothermic, with an energy barrier of 0.61 eV. Accordingly, presence of the oxygen vacancies promotes H-2 dissociation and production of GaH species on the Ga2O3 surfaces. Higher temperatures are expected to favor oxygen vacancy creation on the Ga2O3 surfaces and thereby benefit the production of GaH species. This analysis is consistent with the FTIR results that the bands assigned to GaH species become stronger at higher temperatures.