Modulation of optical and electrical properties of In2O3 films deposited by high power impulse magnetron sputtering by controlling the flow rate of oxygen

Abstract

Herein, highly transparent and conductive In2O3 films were deposited by reactive high power impulse magnetron sputtering from a metal target without thermal assistance. Film deposition was performed at room temperature using oxygen flow rates selected based on target voltage hysteresis, and the obtained films were compared in terms of structure and electrical/optical properties. Notably, the use of high plasma density, peak power, and ionization efficiency resulted in the formation of highly crystalline films featuring a small grain size and a columnar structure with a preferred orientation. The minimal carrier concentration of 1.6 × 1021 cm−3 was observed for films deposited in metallic mode; the carrier mobility of these films increased from 23 to 51 cm2 V−1 s−1 as the oxygen flow rate increased from 7 to 10 sccm. Moreover, the oxygen flow rate significantly affected the conductivity of In2O3 films, which ranged from semiconductor-like to insulator. The visible-light transmittance of In2O3 films exceeded 85% when oxygen flow rate larger than 7sccm. The absorption edge of as-prepared films was located close to 350 nm and shifted to lower wavelengths with increasing oxygen flow rate, which was explained by the Burstein–Moss effect. The infrared transmittance of In2O3 films was strongly dependent on the deposition mode. In agreement with Drude's theory, films deposited in transition mode at room temperature were highly transparent and conductive, which was ascribed to the use of controlled In:O ratios, whereas films deposited in other modes were shown to exhibit either excellent conductivity (metallic mode) or good optical transmittance (poisoning mode).