Ni/ZnO Schottky photodiodes for high-performance ultraviolet detection: Influence of precursor molarity on structural and electrical properties

In this study, ZnO thin films were spin coated on FTO coated glass substrates with varying precursor molarities (0.3 M, 0.5 M, 0.7 M, and 0.9 M). The impact of molarity on the structural, morphological, optical, and electrical properties of the films was comprehensively investigated. X-ray diffraction (XRD) patterns confirmed the hexagonal wurtzite structure of the films, with optimal crystallite size and reduced dislocation density for 0.7 M films. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed uniform film growth with roughness values ranging from 4.6 nm to 9.2 nm. UV–visible spectroscopy showed an absorption edge in the near UV region. Schottky diodes were fabricated using Ni as the top contact. The I–V characteristics showed non-linear behaviour with a rectification of 2 orders for 0.5 M and 0.7 M films. The photoresponse studies indicated significant photocurrent enhancement under UV illumination, with the 0.7 M sample exhibiting a responsivity of 3.5 A/W and detectivity of $2\times {10}^{11}$ Jones. Transient response analysis demonstrated fast switching behaviour with rise and decay times of approximately 3 and 7 s, respectively.