Annealing effects on the structural, optical and electrical properties of Zn₃P₂ thin films prepared by the thermal evaporation technique

Zn₃P₂ films are important for a wide range of optoelectronic applications. Zinc phosphide (Zn₃P₂) thin films were deposited on indium tin oxide (ITO)-coated glass substrates at room temperature by thermal evaporation and subsequently annealed in air at 150, 250, and 350 °C. This study examined the effects of annealing on the structural, optical, and electrical properties of the films. X-ray diffraction (XRD) showed that both the as-deposited and annealed films were amorphous. Scanning electron microscopy (SEM) revealed pronounced changes in surface morphology with increasing annealing temperature. Energy-dispersive X-ray spectroscopy confirmed the presence of Zn and P, with Zn/P atomic ratios of 1.47, 1.48, 1.22, and 1.48 for the as-deposited, 150, 250, and 350 °C samples, respectively. The optical band gaps were 1.532 eV for the as-deposited film and 1.685, 1.662, and 1.630 eV for the films annealed at 150, 250, and 350 °C, respectively. FTIR spectra showed annealing-dependent changes in weak vibrational features, suggesting modifications in the local bonding environment. The electrical resistivity increased markedly from 5.8 × 10⁴ Ω cm for the as-deposited film to 1.6 × 10⁹ Ω cm after annealing at 350 °C.