The origin of electrical property deterioration with increasing Mg concentration in ZnMgO:Ga

Abstract

Transparent conductive Ga-doped Zn1−xMgxO (ZnMgO:Ga) films were epitaxially grown via Pulsed Laser Deposition on sapphire by optimizing the substrate temperature and other parameters of deposition. Zn0.68Mg0.31Ga0.01O/sapphire films deposited at 400°C have a Hall mobility (μ) of 9.2±0.5cm2V−1s−1 and a free electron density (n) of 1.79×1020±0.06×1020cm−3, yielding an electrical conductivity (σ)=262±22S/cm. Zn0.90Mg0.09Ga0.01O/sapphire films, deposited under the same growth conditions, have similar crystalline quality, but significantly better electrical properties (σ=1450±10S/cm, μ=24.5±2.5cm2V−1s−1, n=3.81×1020±0.20×1020cm−3). This comparison provides evidence of electrical property deterioration in doped ZnMgO bulk material with increasing Mg content, independent of crystalline quality. Electrical properties of ZnMgO:Ga are further deteriorated by the decrease of the crystalline quality. Polycrystalline Zn0.90Mg0.09Ga0.01O/a-SiO2 samples deposited under identical conditions on amorphous silica substrates had both inferior crystal quality and inferior transport properties (μ=2.5±0.2cm2V−1s−1, n=2.04×1020±0.20×1020cm−3, σ=80±8S/cm) compared to their epitaxial counterparts. Overall, the results of this study indicate that both bulk material properties and crystalline quality influence the electrical properties of single-phase ZnMgO:Ga thin films.