Synthesis and characterization of Zn1-xMnxS thin films deposited by spray pyrolysis technique

Abstract

Diluted magnetic semiconductor (DMS) thin films (A1-xMxB) are prepared by doping a particular amount of magnetic element (M) into II (A)-VI (B) semiconductor. Zn1-xMnxS with varying Manganese (Mn) concentrations or x = 0.00, 0.10, 0.30, 0.50 and 0.70 mole were synthesized on glass substrates using Spray Pyrolysis Deposition (SPD) technique. An aqueous solution containing Zinc acetated, Manganese acetated and thiourea for Zinc ions (Zn+2), Manganese ions (Mn+2) and sulfide ions (S-2) respectively were used to deposit Zn1-xMnxS thin films at 3500C substrate temperature. The ratio of Zinc acetated, Manganese acetate and thiourea were 1:1:2. The films were characterized by Scanning Electron Microscopy (SEM), energy dispersive X-ray spectrometer (EDX), X-ray diffractometer (XRD), ultraviolet visible light (UV-vis) spectroscopy and Van-der Paw method for electrical property. The results showed that deposition time, temperature, and Mn doping concentration can affect the composition, surface morphology, crystallinity, grain size, and transmission spectra of the films. All the films were annealed at 4500C and 5500C for 1h. All as deposited films showed amorphous in nature and annealed films showed crystalline nature. SEM micrographs showed that the surface morphology of as-deposited Zn1-x MnxS films was inhomogeneous and after annealing the films became homogeneous. Some fibrous like structure was found into the annealed ZnS and Zn1-x MnxS films showed some crystallographic shape which confirmed the presence of Mn into ZnS. EDX spectra revealed the presence of Zn, Mn and S peaks in the films. All XRD patterns showed that crystallinity of the films increased with increasing Mn concentration. The size of the particles increased as the annealing temperature was increased. XRD patterns of the 5500 C annealed samples with different Mn concentrations (0.00, 0.10, 0.30, and 0.50 mole) showed polycrystalline nature. UV-vis transmission spectroscopy showed that the films were highly transparent (>80%) in the visible region. The optical direct band gap of as-deposited films was decreased from 3.51 eV to 3.01eV and indirect band gap from 3.02eV to 1.85eV with increasing Mn concentrations. This indicated that the presence of Mn in the system greatly affected the optical bad gap. The electrical conductivity and activation energy increased with increasing Mn concentrations. The dc conductivity was 10-3 order and activation energy changed from 0.14 eV to 0.45 eV. Also the increase of electrical conductivity with the increase of temperature indicated semi conducting behavior of as-deposited films.