Hidden Hydrogen in β-Ga₂O₃

Hydrogen impurities may play a crucial role in the electrical conductivity of β-Ga₂O₃ by acting as shallow donors and by passivating cation-vacancy acceptor complexes [1,2]. IR spectroscopy of β-Ga₂O₃ single crystals treated in an H₂ (D₂) ambient yields a strong, polarized vibrational line at 3437 (2546) cm^-1 originating from a defect containing two equivalent O-H(D) partners. Theoretical calculations using the CRYSTAL06 code [3] with hybridized DFT Hamiltonian yield a plausible model for this defect in which the two H(D) are associated with a relaxed Ga(1) vacancy[4]. The observed production of this defect under a two-step annealing process[5] signifies the existence of “hidden” hydrogen that acts as a source of H not readily seen in vibrational spectroscopy. Candidates for this species, including H₂ at interstitial or vacancy sites, are analyzed theoretically.
[1] J. B. Varley et al., Appl. Phys. Lett. 97, 142016 (2010).
[2] J. B. Varley et al., J. Phys.: Condens. Matter 23 (2011), 334212.
[3] R. Dovesi et al., Crystal06 User’s Manual (University of Torino, Torino, 2006).
[4] P. Weiser, M. Stavola, W. B. Fowler, Y. Qin, and S. Pearton, to be published.
[5] Y Qin et al., this meeting.