Terahertz time-domain spectroscopy of ZnO thin films and nanostructures

Abstract

The need of modern technology is to investigate new materials with rich fundamental physics and diverse technological applications. ZnO is a typical transparent conductive material (TCO) extensively studied for its UV photo sensing and gas sensing applications. The conductivity of the films and nanostructures under UV illumination is an important property that governs the feasibility for practical applications. THz radiation can be used to examine material systems without affecting them to change their current states because of its low energy. As a result, it is a non-perturbative technique for material study. In this work, we have used PLD and GLAD techniques to deposit highly crystallographically aligned ZnO thin films and nanostructures on Quartz substrate. Further, we have studied the effect of the environment and UV illumination on the conductivities of the two samples using Terahertz Time-Domain Spectroscopy (THz-TDS). It was found that, in comparison to thin film, the porosity of the nanostructures was significantly high. Further, when compared to thin films, the conductivity of nanostructures decreases by an order due to increased adsorption of nitrogen and oxygen gases which results in band bending. Furthermore, the conductivities in vacuum environment are higher than nitrogen atmosphere both in the presence and absence of UV light. The conductivities of both samples increase monotonously with increasing UV light intensity.