Preparation and characterization of II -VI semiconductor thin film by spray pyrolysis

Abstract

Zn1-xCdxS thin films with different values of x (viz. 0, 0.2, 0.4, 0.6, 0.8 and1) have been prepared by spray pyrolysis onto glass substrates at 523 K. The surface morphology, structural, optical and electrical properties of the as-deposited films were studied by optical microscope, XRD, UV-Visible spectroscopy and van-der Pauw method. The as-deposited film Zn0.2Cd0.8S was annealed at different temperatures. The films Zn1-xCdxS have inhomogeneous surfaces, less defined grain boundaries. The elemental compositions have been estimated by Energy Dispersive X-ray Analysis (EDX) which reveal that the deposited films are very close to the nominal composition. X-ray diffraction patterns have been taken on Zn0.2Cd0.8S thin films of as-deposited and annealed for1 hour at different temperatures. The as-deposited film has a broad peak indicating amorphous in nature. After annealing the sample was found to be in crystalline nature. Lattice constant was found to be 4.676 Å. Structure of the material has been identified as cubic. Average grain size of the thin film is found to be in the range of 8 to 47 nm. Average grain size of the film increases with the increase of annealing temperature. Various optical constants such as optical band gap, refractive index, extinction coefficient, dielectric constant, dielectric loss and optical conductivity of the films have been studied. For different compositions of asdeposited Zn1-xCdxS films, the optical band gap is varied from 3.60 to 2.42 eV as x changes from 0 to 1. The optical band gaps of Zn0.2Cd0.8S films are observed to decrease from 2.6 to 2.1 eV with the increase of annealing temperature. The increase of electrical conductivity with the increase of temperature indicates that both the as deposited and annealed films are semiconductor in nature. Activation energies of Zn1-xCdxS films are found to increase with the incorporation of Cd.