Voltage-driven electro-spray and optoelectronic evaluation of Gadolinium-doped Zirconium sulphide thin films for enhanced optoelectronic and photonic device applications

Abstract

In this study, Gd-doped zirconium sulphide (ZrS/Gd) thin films were synthesized by electro-spray deposition at 10.5, 11.0, and 11.5 V to evaluate their structural, optical, and electrical properties. UV–Vis analysis showed enhanced UV absorption (300–400 nm), reaching 0.75 a.u. at 11.5 V, while visible transmittance reached approximately 85%. The optical bandgap increased from 3.19 eV for pristine ZrS to 3.62 eV at 11.5 V, indicating that the energy bandgap increased with applied voltage. This can be explained by changes in the material's electrical structure when exposed to an external electric field, charge redistribution, or quantum confinement effects. Optical conductivity reached 0.73 S/m, and the refractive index peaked at 3.0 around 3.4 eV. Electrical conductivity increased from 1.65 S/m for pristine ZrS to 1.89 S/m at 11.5 V, accompanied by a resistivity decrease from 0.61 to 0.53 Ω·m. The crystallite size remained relatively constant at 801.28–801.35 nm, whereas FWHM increased from 0.1034° to 0.1272° with increasing deposition voltage. FTIR spectra showed O–H vibrational features around 3500–3800 cm⁻¹ and lower-wavenumber bands associated with Zr–S and possible Gd–O vibrations. I–V measurements revealed a pronounced current increase beyond 0.4 V for the 11.5 V sample, indicating threshold-like electrical behaviour. SEM revealed relatively uniform films with nanoparticle agglomeration and no obvious pinholes. Therefore, Gd incorporation and deposition-voltage variation significantly influenced the optical and electrical characteristics of ZrS/Gd films, demonstrating their potential for optoelectronic and photonic applications.