Substrate temperature dependence of growth mode, microstructure and optical properties of highly oriented zinc oxide films deposited by reactive sputtering

Abstract

Polycrystalline ZnO films were deposited on quartz substrates by reactive sputtering of zinc target. X-ray powder diffraction, pole figure analysis and high resolution measurements along with transmission electron microscopy, Raman and photoluminescence studies were carried out to study the microstructure, crystallinity and optically active defects in the films. All the films deposited in the substrate temperature range from room temperature to 600 °C exhibited strong c-axis preferred orientation. The changes in preferred orientation of crystallites with substrate temperature were attributed to its being determined by preferential nucleation at lower temperatures and surface diffusion at higher temperatures. A detailed microstructural analysis showed that with increase in substrate temperature from 300 °C to 600 °C, a significant reduction in micro-strain to ∼ 10 − 3 takes place, along with a marginal increase in crystallite size. Raman and photoluminescence studies have shown that the films deposited below 300 °C possessed poor crystalline quality. The film deposited at 600 °C yielded the most intense and narrow (∼ 102 meV) band edge luminescence at room temperature, though it did not exhibit the strongest c-axis orientation of crystallites. This is attributed to its superior crystalline quality and absence of oxygen-deficiency related defects.