Hydrogen on polycrystalline β-Ga2O3: Surface chemisorption, defect formation, and reactivity

The adsorption of H2 and H2O on differently pretreated β-Ga2O3 samples, exhibiting variable surface chemistry and surface defect concentration, was studied by temperature-programmed reduction, oxidation, and desorption; Fourier transform infrared spectroscopy; and electric impedance measurements. Adsorption of H2 at 300–473 K resulted in the formation of surface OH groups with no formation of oxygen defects. Between 473 and 550 K, formation of Ga–H species was observed. At above 550 K, oxygen vacancy/defect formation was observed, resulting in enhanced formation of Ga–H species, accompanied by the formation of more strongly bound Ga–H species. H2O was observed to quench oxygen vacancies formed by reductive pretreatment and to exhibit a strong hydrolytic affinity to H adsorbed on Ga sites. The effect of water was seen even under strongly reducing conditions (773 K; 1 bar H2) with only traces of water present.