High transparent and conductive undoped ZnO thin films deposited by reactive ion-beam sputtering

Abstract

High transparent and conductive undoped ZnO thin films deposited by reactive ion-beam sputtering on Si and glass substrates were studied. Our films were found to be polycrystalline ones having a hexagonal wurtzite structure with c-axis preferred orientation. In the course of experiments employing X-ray diffraction, energy dispersive X-ray analysis, multi-angle spectral ellipsometry, atomic force microscopy, optical transmission/reflection and electrical measurements, the influences of substrate temperature and accelerating voltage on the structural, optical and electrical properties of ZnO thin films were revealed and discussed. It was shown that the beneficial conditions for the growth of high-quality film are as follows: substrate temperature ranging in 200–250 °C and acceleration voltage ranging in 5–6 keV. O-rich condition of deposition helped to obtain p-type conductivity, which, however, was not stable over time. The best films with thickness nearly 100 nm demonstrated resistivities of ∼2 mOhm∙cm, being 86% transparent in visible light. Also, free electron concentration of ∼2 × 1020 cm−3 and mobility of ∼17 cm2 V−1s−1 were achieved. All this implies that the as-grown undoped ZnO films are promising for the application as high conductive transparent electrodes.