Study on corundum-structured p-type iridium oxide thin films and band alignment at iridium oxide /gallium oxide hetero-junction

Corundum-structured iridium oxide, showing p-type conductivity, is a powerful candidate material for forming high-quality pn hetero-junctions with gallium oxide. We have succeeded in fabricating corundum-structured iridium oxide thin films on sapphire substrates. According to the optical transmittance measurement, the optical bandgap of iridium oxide was found to be approximately 3.0 eV. Furthermore, the band alignment at the iridium oxide /gallium oxide interface was investigated by X-ray photoemission spectroscopy, revealing a staggered-gap (type-II) with the valence and conduction band offsets of 3.3 eV and 1.0 eV, respectively.