Electronic Structure and Light-Induced Conductivity of a Transparent Refractory Oxide

Combined first-principles and experimental investigations reveal the underlying mechanism responsible for a drastic change of the conductivity (by 10 orders of magnitude) following hydrogen annealing and UV irradiation in a transparent oxide, $12\mathrm{C}\mathrm{a}\mathrm{O}\ifmmode\cdot\else\textperiodcentered\fi{}7{\mathrm{A}\mathrm{l}}_{2}{\mathrm{O}}_{3}$, found by Hayashi et al. [Nature (London) 419, 462 (2002).] The charge transport associated with photoexcitation of an electron from ${\mathrm{H}}^{\ensuremath{-}}$ occurs by electron hopping. We identify the atoms participating in the hops, determine the exact paths for the carrier migration, estimate the temperature behavior of the hopping transport, and predict a way to enhance the conductivity by specific doping.