DFT theoretical and experimental investigations of the effect of Cu doping within SILAR deposited ZnS

Abstract

In this work, the effect of copper doping within ZnS on glass substrates was studied using integrated theory and experiments. Experimentally the pure ZnS and Cu-doped ZnS, for a variety of Cu concentrations (2 %, 4 %, 6 %), were grown, on a glass substrate, using the SILAR technique with 30 deposition cycles. Theoretically, the full potential linearized enhanced plane wave (FP-LAPW) approach based on density functional theory (DFT), using the TB-mBJ and PBE_GGA approximations, was employed to study the structural, electronic, and optical properties of copper-doped ZnS. The structural, morphological, and optical properties of deposited films were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and ultraviolet–visible-Near Infrared spectroscopy. XRD patterns demonstrate that all films were polycrystalline which corresponds to the hexagonal wurtzite with the (103), (104), and (105) directions as the preferred orientation. The crystalline particle size of the samples decreased, suggesting a change in crystallinity with Cu doping. The surface morphology showed that pure ZnS and Cu-doped ZnS present a rough, granular surface. EDX analysis confirms the expected dopant element presence in ZnS film. UV spectrophotometry experiments reveal that Cu incorporation causes a slight decrease in the optical gap energy from 3.74 to 3.67 eV, which confirms that the Cu atom reduces the band gap of this material.