Ultrathin high-mobility hydrogen-doped indium oxide films

Hydrogen-doped indium oxide (IHO) is a unique photonic material because of its high carrier mobility, strong plasma dispersion effect, and low optical absorption at both visible and near-infrared wavelengths. Existing research has mostly focused on films thicker than 100 nm, which is different from their potential role as an electro-optic material in photonic integrated circuits, where ultrathin films are required. This study examined IHO films with thicknesses ranging from 6 to 88 nm by characterizing their morphologies, electrical, and optical properties. The carrier mobility increased from 36 to 112 cm 2 /V·s with increasing thickness owing to the reduced grain boundary electron scattering. Additionally, we observed that IHO films thinner than 25 nm exhibited significant mobility loss after 8 months of exposure to air but were fully recovered by re-annealing at 230 °C in a nitrogen gas environment, which might be attributed to reactivated hydrogen dopant.