Formation of the E 4 * level in implanted β − Ga 2 O 3

Deep-level transient spectroscopy measurements were conducted on He-implanted $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}₂{\mathrm{O}}₃$ thin films to study the ${E}₄^*$ level, which is a known irradiation-induced defect that is energetically positioned $1.5\phantom{\rule{0.16em}{0ex}}\mathrm{e}\mathrm{V}$ below the conduction band minimum. We find that the formation of ${E}₄^*$ after implantation is strongly dependent on a reverse-bias annealing step, where the activation energy for the thermally-activated introduction of ${E}₄^*$ is estimated to be $\ensuremath{\sim}2.4\phantom{\rule{0.16em}{0ex}}\mathrm{e}\mathrm{V}$. Contrary to previous reports, we find, for some of the measured diodes, that the level is stable upon subsequent measurements. From first-principles calculations of the intrinsic defects, we find that the properties of the ${V}_{\text{O1}}$ and ${V}_{\text{O3}}$ configurations of the oxygen vacancy closely agree with the experimental observations for the ${E}₄^*$ level. A model is suggested where the reverse bias lowers the Fermi-level position in the depletion region of the diode and changes the relative formation energies of the possible configurations of the oxygen vacancy; the formation of ${E}₄^*$ then results from an increase in the relative stability of the O1 and O3 configurations of ${V}_{\mathrm{O}}$.