Indium-based ultraviolet-transparent electroconductive oxyfluoride InOF: ambient-pressure synthesis and unique electronic properties in comparison with In2O3.

A method for the synthesis of single-phase powdered InOF under ambient pressure has been developed. The method involves pyrolysis of a hydrate of InF3 in an O2 atmosphere of controlled humidity. Various intermediate phases were formed during the pyrolysis, and their structures and interconversions were analyzed. Combined results of optical absorption measurements and density functional calculations indicate that InOF is a direct band gap material with a band gap energy of ∼3.7 eV. Unlike In2O3, the electrical conductivity of polycrystalline InOF pellets can be controlled over ∼8 orders of magnitude from ∼10(-8) S cm(-1) to ∼2 S cm(-1) by thermal annealing, and the sample with the highest conductivity was a nearly degenerate n-type semiconductor with a relatively small carrier concentration of ∼10(18) cm(-3). The work function of InOF measured by ultraviolet photoelectron spectroscopy is ∼3.5 eV and is smaller by ∼1.5 eV than that of In2O3. This difference comes from a decrease in the electron affinity.