The Origin of Electrical Property Deterioration with Increasing Mg Concentration in ZnMgO:Ga

Transparent conductive Ga-doped Zn _1-xMg _xO (ZnMgO:Ga) films were epitaxially grown via Pulsed Laser Deposition on sapphire by optimizing the substrate temperature and other parameters of deposition. Zn _0.68Mg _0.31Ga _0.01O/sapphire films deposited at 400°C have a Hall mobility (μ) of 9.2 ± 0.5 cm ² V ^-1 s ^-1 and a free electron density (n) of 1.79 × 10 ²⁰ ± 0.06 × 10 ²⁰ cm ^-3, yielding an electrical conductivity (σ) = 262 ± 22 S/cm. Zn _0.90Mg _0.09Ga _0.01O/sapphire films, deposited under the same growth conditions, have similar crystalline quality, but significantly better electrical properties (σ = 1450 ± 10 S/cm, μ = 24.5 ± 2.5 cm ² V ^-1 s ^-1, n = 3.81 × 10 ²⁰ ± 0.20 × 10 ²⁰ cm ^-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 Zn _0.90Mg _0.09Ga _0.01O/a-SiO ₂ samples deposited under identical conditions on amorphous silica substrates had both inferior crystal quality and inferior transport properties (μ = 2.5 ± 0.2 cm ² V ^-1 s ^-1, n = 2.04 × 10 ²⁰ ± 0.20 × 10 ²⁰ cm ^-3, σ = 80 ± 8 S/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.