STRUCTURAL AND OPTICAL PROPERTIES OF PHOSPHOROUS AND ANTIMONY DOPED ZNO THIN FILMS DEPOSITED BY SPRAY PYROLYSIS: A COMPARATIVE STUDY

Abstract: A study of structural and properties of pure (undoped) Zinc oxide (ZnO) and phosphorous (P) and Antimony (Sb) doped Zinc Oxide films has been carried out. The films were deposited by an automated spray pyrolysis equipment on both microscope glass at various elevated temperatures (270 oC - 420 oC) and on fluorine doped tin Oxide (FTO) substrates at 420 oC. Structural characterization using Raman spectroscopy showed the presence of the main peak for ZnO at 437 cm-1for all the films. Antimony doped films showed other peaks associated with the doping but phosphorous doping did not show extra peaks. Optical characterization using a UV-VIS-NIR Shimadzu (Model DUV 3700) double beam spectrophotometer provided both reflectance and transmittance data and Scout software was used to compute the band gap. At a wavelength of 600 nm, the average transmittance of the pure ZnO films was ~62 % while it was transmittance was ~85 % and ~80 % for Sb and P doped films respectively, an increase of ~23 % and ~18 % respectively. For the undoped ZnO films, high deposition temperatures led to band gap narrowing from 3.25eV to 3.10eVwhile doping resulted in band gap widening from 3.10 eV to 3.30 eV (for P-doped) and 3.10 eV to 3.33 eV (for Sb-doped),an observation confirmed by the increased transmittance on doping. The band gap narrowing for ZnO films makes the film become a better materials for visible light absorption which is good for photovoltaic applications. The wide gap broadening on doping makes the film more transparent to solar radiation making it suitable for transparent conducting oxide applications.

Keywords: Spray pyrolysis, Band gap, optical characterization, resistivity, doped ZnO, Transparent conducting oxides, photovoltaics