Nondegenerate polycrystalline hydrogen-doped indium oxide (Inox:H) thin films formed by low-temperature solid-phase crystallization for thin film transistors

Abstract

We successfully demonstrated a transition from a metallic InOx film into a nondegenerate semiconductor InOx:H film. A hydrogen-doped amorphous InOx:H (a-InOx:H) film, which was deposited by sputtering in Ar, O2, and H2 gases, could be converted into a polycrystalline InOx:H (poly-InOx:H) film by low-temperature (250◦ C) solid-phase crystallization (SPC). Hall mobility increased from 49.9 cm2 V−1 s−1 for an a-InOx:H film to 77.2 cm2 V−1 s−1 for a poly-InOx:H film. Furthermore, the carrier density of a poly-InOx: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-InOx channel did not show any switching properties. In contrast, that with a 50 nm thick nondegenerate poly-InOx:H channel could be fully depleted by a gate electric field. For the InOx:H TFTs with a channel carrier density close to the MIT point, maximum and average field effect mobility (µFE ) values of 125.7 and 84.7 cm2 V−1 s−1 were obtained, respectively. We believe that a nondegenerate poly-InOx:H film has great potential for boosting the µFE of oxide TFTs.