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

Abstract Transparent conductive Ga-doped Zn 1 − x Mg x O (ZnMgO:Ga) films were epitaxially grown via Pulsed Laser Deposition on sapphire by optimizing the substrate temperature and other parameters of deposition. Zn 0.68 Mg 0.31 Ga 0.01 O/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 0.90 Mg 0.09 Ga 0.01 O/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 0.90 Mg 0.09 Ga 0.01 O/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.