Self-Powered UV Photodetectors Based on Heterojunctions Composed of ZnO Nanorods Coated with Thin Films of ZnS and CuI
Akshai Shyam, NandaKumar Amal Kaitheri, R. Ramesh, S. Ramasubramanian
Abstract
A simple, inexpensive solution process is used to deposit γ-CuI thin films, and many aspects of the films, such as morphology, crystalline phase, and its optical and electrical properties on annealing are studied. All of the grown films exhibited p-type conductivity and an average transmittance of 70 to 80% in the visible region. The film annealed at 200 °C is observed to be relatively smooth with root-mean-square roughness of 13.25 nm. CuI films annealed at 200 °C displayed a hole mobility of 0.53 cm 2 /Vs and a hole concentration of 8.36 × 10 18 cm –3 . Additionally, the potential of γ-CuI as a p-type material for photodetection is explored by fabricating transparent hybrid ultraviolet (UV) photodetectors based on p- CuI/ n- ZnO nanorods and p- CuI/ n- ZnS/ZnO nanostructures. The high-resolution transmission electron microscopy (HRTEM) image showed that the ZnO nanorods grew as a single crystal along the [001] direction and smaller CuI attached on their surface. A simple sulfurization procedure has created a poly-nanocrystalline ZnS shell layer over the ZnO nanorods. Crucial photodetector parameters such as responsivity, external quantum efficiency, and detectivity are analyzed with different illumination intensities and incident wavelengths. Under self-powered conditions, upon illumination with 372 nm and intensity of 0.25 mW/cm 2, the p- CuI/ n- ZnO nanorod showed significant responsivity of 25.11 mA/W and detectivity of 4.59 × 10 13 Jones. Insertion of the ZnS layer between the ZnO and CuI has enhanced these parameters to 43.85 mA/W and 3.84 × 10 14 Jones, respectively. This research underlines the potential of p-type CuI as a transparent, high-performance optoelectronic material.