Effect of thickness on the properties of ZnO thin films prepared by reactive RF sputtering

This work reports structural and electrical properties of ZnO thin film deposited by reactive RF sputtering at the room temperature, for thin film transistor (TFT) applications. To study the thickness dependent effect, ZnO thin film of thicknesses 100, 200 and 800 nm were deposited over p-type silicon substrate. Structural properties of thin films have been characterized using X-ray Diffraction (XRD) and Atomic Force Microscopy (AFM). XRD analysis of 100 and 200 nm thick films shows dominant cubic phase of ZnO along with small presence of ZnO₂, while; XRD analysis of 800 nm thick film confirms strong c-axis growth of wurtzite (W) ZnO. The XRD result confirm the polycrystalline nature of the thin film and shows that crystallinity improves with the film thickness. The AFM results confirm high step coverage of deposited thin films. From the thermionic transport model across the grain boundary it was observed that with an increase in film thickness mobility of carriers increases. The sheet resistance of undoped 100 and 200 nm ZnO film is found to be approximately 7 × 10¹¹ Ω/□; while, the sheet resistance of 800 nm thick ZnO film shows almost 10 time reduction to 6.025 × 10¹⁰ Ω/□, owing to its improved crystallinity.