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

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. Zn0.68- Mg0.31Ga0.01O/sapphire films deposited at 400 degrees C have a Hall mobility (mu) of 9.2 +/- 0.5 cm(2) V-1 s(-1) and a free electron density (n) of 1.79 x 10(20) +/- 0.06 x 10(20) cm(-3), yielding an electrical conductivity (sigma) = 262 +/- 22 S/cm. Zn0.90Mg0.09Ga0.01O/sapphire films, deposited under the same growth conditions, have similar crystalline quality, but significantly better electrical properties (sigma = 1450 +/- 10 S/cm, mu = 24.5 +/- 2.5 cm(2) V-1 s(-1), n = 3.81 x 10(20) +/- 0.20 x 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 Zn0.90Mg0.09Ga0.01O/a-SiO2 samples deposited under identical conditions on amorphous silica substrates had both inferior crystal quality and inferior transport properties (mu = 2.5 +/- 0.2 cm(2) V-1 s(-1), n = 2.04 x 10(20) +/- 0.20 x 10(20) cm(-3), sigma = 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. (c) 2012 Elsevier B.V. All rights reserved.