High electron doping to a wide band gap semiconductor 12CaO∙7Al2O3 thin film

High-density electrons (∼1.9×1021cm−3) were doped into a polycrystalline film of a wide band gap (∼7eV) semiconductor 12CaO∙7Al2O3 (C12A7) by an in situ postdeposition reduction treatment using an oxygen-deficient C12A7 overlayer. The resultant film exhibits metallic conduction with a Hall mobility of ∼2.5cm2V−1s−1 and a conductivity of ∼800Scm−1. Optical analyses indicate that most of the doped electrons behave as free carriers with an effective mass of 0.82me and the estimated in-grain mobility is 5.2cm2V−1s−1, which agrees reasonably with the value obtained for high-quality single crystals.