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 cm2V−1s−1 for an a-InOx:H film to 77.2 cm2V−1s−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 cm2V−1s−1 were obtained, respectively. We believe that a nondegenerate poly-InOx:H film has great potential for boosting the μFE of oxide TFTs.

Influence of Grain Boundary Scattering on the Field-Effect Mobility of Solid-Phase Crystallized Hydrogenated Polycrystalline In2O3 (In2O3:H)

“…In general, for degenerate transparent conducting oxide materials, the mobility in the grains is determined by an optical method using the Drude model, because optical mobilities are not affected by grain boundary scattering [ 32 , 33 ]. However, it is difficult to determine the optical mobility of In 2 O 3 :H films annealed at T ann ≥ 250 °C because the free electrons are significantly decreased to the order of 10 17 cm −3 and the films become non-degenerate semiconductors [ 34 , 35 ]. Therefore, we evaluated the effects of intragrain scattering by measuring the field-effect mobility of In 2 O 3 :H TFTs.…”

Nucleation and grain growth in low-temperature rapid solid-phase crystallization of hydrogen-doped indium oxide

“…For TFT applications, Magari and Kataoka et al demonstrated poly-InO x :H TFTs with field-effect mobility of 139 cm 2 Vs −1 . [30][31][32] Most of the research on SPC poly-InO x :H films has focused on film thickness of more than 100 nm for TCO applications. On the other hand, there are few papers on the study of SPC poly-InO x :H for TFT applications with a thickness of less than 50 nm.…”