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We have recently discovered an O-H vibrational line at 3427 cm^-1 in beta-Ga₂O₃. This line was found to be strongly polarized along the [010] direction of a (-201)-oriented wafer and has been assigned to a V_Ga-2H complex [1]. Surprisingly, this defect has been found to be most effectively produced by a two-step annealing process. A first anneal in an H₂ ambient at 900°C produces a weak line at 3437 cm^-1. A second anneal in flowing N₂ at 450°C greatly increases the intensity of the 3437 cm^-1 line. These results show that a “hidden” form of H can be produced in Ga₂O₃ that can be converted into the V_Ga-2H complex by an addition thermal annealing treatment in an inert ambient. Similarly, the implantation of protons into Ga₂O₃ at room temperature produces a weak line at 3427 cm^-1 that is made roughly 4 times more intense by a subsequent anneal at 450°C. The identity of this “hidden” form of H in Ga₂O₃ remains as a puzzle.
[1] P. Weiser, M. Stavola, W. B. Fowler, Y. Qin, and S. J. Pearton, to be published.