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

We successfully demonstrated a transition from a metallic InO x film into a nondegenerate semiconductor InO x :H film. A hydrogen-doped amorphous InO x :H (a-InO x :H) film, which was deposited by sputtering in Ar, O 2 , and H 2 gases, could be converted into a polycrystalline InO x :H (poly-InO x :H) film by low-temperature (250 °C) solid-phase crystallization (SPC). Hall mobility increased from 49.9 cm 2 V -1 s -1 for an a-InO x :H film to 77.2 cm 2 V -1 s -1 for a poly-InO x :H film. Furthermore, the carrier density of a poly-InO x :H film could be reduced by SPC in air to as low as 2.4 × 10 17 cm -3 , which was below the metal-insulator transition (MIT) threshold. The thin film transistor (TFT) with a metallic poly-InO x channel did not show any switching properties. In contrast, that with a 50 nm thick nondegenerate poly-InO x :H channel could be fully depleted by a gate electric field. For the InO x :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 cm 2 V -1 s -1 were obtained, respectively. We believe that a nondegenerate poly-InO x :H film has great potential for boosting the μ FE of oxide TFTs.