Nondegenerate Polycrystalline Hydrogen-Doped Indium Oxide (InO:H) Thin Films Formed by Low-Temperature Solid-Phase...

We successfully demonstrated a transition from a metallic InO film into a nondegenerate semiconductor InO:H film. A hydrogen-doped amorphous InO:H (a-InO:H) film, which was deposited by sputtering in Ar, O₂, and H₂ gases, could be converted into a polycrystalline InO:H (poly-InO:H) film by low-temperature (250 °C) solid-phase crystallization (SPC). Hall mobility increased from 49.9 cm²V^-1s^-1 for an a-InO:H film to 77.2 cm²V^-1s^-1 for a poly-InO:H film. Furthermore, the carrier density of a poly-InO:H film could be reduced by SPC in air to as low as 2.4 × 10¹⁷ cm^-3, which was below the metal-insulator transition (MIT) threshold. The thin film transistor (TFT) with a metallic poly-InO channel did not show any switching properties. In contrast, that with a 50 nm thick nondegenerate poly-InO:H channel could be fully depleted by a gate electric field. For the InO:H TFTs with a channel carrier density close to the MIT point, maximum and average field effect mobility (μ_FE) values of 125.7 and 84.7 cm²V^-1s^-1 were obtained, respectively. We believe that a nondegenerate poly-InO:H film has great potential for boosting the μ_FE of oxide TFTs.