Influence of heat treatments in H2 and Ar on the E1 center in β-Ga2O3

The influence of heat treating n-type bulk β-Ga2O3 in hydrogen (H2) and argon (Ar) gases on the presence of the defect level commonly labeled as E1 was studied. Fourier transform-infrared spectroscopy confirms that hydrogen (H) is incorporated into β-Ga2O3 during H2 annealing at 900 °C. Deep-level transient spectroscopy measurements reveal that the concentration of the E1 level is promoted by the introduction of H, in contrast to what is observed in samples heat-treated in an Ar flow. We further find the E1 level to be stable against heat treatments at 650 K, both with and without an applied reverse-bias voltage. Potential candidates for the defect origin of E1 are investigated using hybrid-functional calculations, and three types of defect complexes involving H are found to exhibit charge-state transition levels compatible with E1, including substitutional H at one of the threefold coordinated O sites, Ga-substitutional shallow donor impurities passivated by H, and certain configurations of singly hydrogenated Ga–O divacancies. Among these types, only the latter exhibit H binding energies that are consistent with the observed thermal stability of E1.