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.