Study of Optical Properties of Nanocrystalline Zinc Phosphide Thin films

Abstract

Zinc phosphide (Zn3P2), a II–V group semiconductor compound has long been considered as a very interesting and suitable candidate for several applications especially in photovoltaics. Nanocrystalline Zn3P2 thin films were successfully synthesized on glass and different silicon-based substrates by a combined physico-chemical method. The properties and morphology of Zn3P2 films were investigated. SEM images showed that all films displayed a nanoscale granular, polycrystalline morphology. It depends dramatically on the surface state of the substrate and follows the substrate its morphology. X-ray diffraction (XRD) spectra revealed a preferred orientation of the Zn3P2 nanocrystalline film along the (102) and (405) direction. The transmittance of the Zn3P2 films was found to be high of the order of 87%. The optical gap of the film was determined using the optical transmission spectra and the obtained optical band gap value is 1.96 eV. A decrease of the average reflectance from 15% to 4.25%, after deposition of the nanocrystalline Zn3P2 on a textured Si substrate, was observed. This result was compared to the one obtained with SiNx layer deposited on the same Si substrate. A difference of 1% was noticed. We assume that the combination of nanocrystalline Zn3P2 thin film and a textured Silicon surface could increase the efficiency of photovoltaic silicon solar cell by using Zn3P2 as an antireflection layer.