Vibrational properties of an OH center in $\beta \quad -$\textbf{Ga}$_{\mathbf{2}}$\textbf{O}$_{\mathbf{3}}$

Theoretical predictions suggest that hydrogen impurities play a crucial role in the electrical conductivity of $\beta -$Ga$_{2}$O$_{3}$ by acting as shallow donors and by passivating cation-vacancy acceptor complexes [1,2]. IR spectroscopy of $\beta -$Ga$_{2}$O$_{3}$ single crystals treated in an H$_{2}$ (D$_{2})$ ambient display a strong vibrational line at 3437 (2546) cm$^{-1}$ originating from an O-H(D) containing defect. This line is thermally stable at 1000$^{\circ}$ C, which suggests that it may arise from a V$_{Ga}$-H complex. Theoretical calculations using the CRYSTAL06 code [3] with hybridized DFT Hamiltonian and the polarization properties of the O-H vibrational line are used to determine possible microscopic structures for this defect and other possible defects. [1] J. B. Varley \textit{et al.}, Appl. Phys. Lett. \textbf{97}, 142016 (2010). [2] J. B. Varley \textit{et al.}, J. Phys.: Condens. Matter \textbf{23} (2011), 334212. [3] R. Dovesi \textit{et al.}, \textit{Crystal06 User's Manual} (University of Torino, Torino, 2006).