A comparative study of the structural and optical properties of ZnO films synthesized through spray pyrolysis and hydrothermal growth

Abstract

This study correlates growth temperature with the UV-A sensitivity of zinc oxide (ZnO) thin films and nanostructures. ZnO thin films were deposited on GaAs (100) substrates via spray pyrolysis, while ZnO nanostructures were synthesized on GaAs (100) substrates using a two-step process involving spray pyrolysis of a zinc acetate precursor to form a seed layer, followed by hydrothermal growth using zinc acetate and hexamethylenetetramine (HMTA). For both materials, two conditions were compared: as-grown samples and post-heat treatment at 350°C. Structural characterizations were done via X-ray Diffractometer and micro-Raman spectroscopy. XRD patterns confirmed the wurtzite phase of ZnO for all synthesized samples. Spray-deposited films exhibited broader diffraction peaks and prominent defect-related visible emission, indicative of smaller crystallite sizes. Subsequent hydrothermal growth promoted further grain evolution, resulting in enhanced crystalline ordering and the suppression of visible photoluminescence (PL) associated with deep-level defects. Thermal annealing further enhanced the near-band-edge (NBE) emission and UV-A radiative efficiency, particularly for the hydrothermal samples. These results indicate that the sequential application of a spray-deposited seed layer and hydrothermal growth, combined with post-growth annealing, improves the structural and optical quality of ZnO/GaAs, demonstrating its potential for UV-A optoelectronic applications.