SYNTHESIS AND OPTICAL CHARACTERISATION OF BORON DOPED ZINC OXIDE THIN FILM USING ELECTROSTATIC DEPOSITION METHOD.

Abstract

ABSTRACT ZnO thin film was doped with boron doping concentration of 5, 10, 15 and 20%, using electrostatic spray deposition method. The study on the effect on the optical properties of the thin film was carried out. The absorbance data, as-deposited, of the boron-doped ZnO (ZnO:B) thin films was obtained using UV-Visible spectroscopy at room temperature in the wavelength range of 350 – 80nm. A sharp absorption peak was observed at 370nm for undoped ZnO (0% Boron doping),the absorption peak slightly shifted to a lower wavelength when the material was doped with concentration of 5 and 10% of Boron, and significantly shifted to a much lower wavelength when doped with 15 and 20% of Boron concentration. The shift indicated the presence of Boron in ZnO thin films. The transmittance, absorption coefficient (α), optical bandgap, refractive index and extinction coefficient were evaluated from the absorbance data. The transmittance (T) of the films increased with the increase of boron concentration which was attributed to the decrease in free carrier absorption due to the elevated carrier mobility of the film. The films generally exhibit relatively poor optical transmission below 70%) which may be connected to film thickness. The optical bandgap(Eg) was found to be between 3.16 and 3.28 eV, the optical bandgap increased as the boron concentration increased from 0 to 20%, this observation can be attributed to the Burstein - Moss (B-M) effect. Refractive index (n) of ZnO:B thin films is found between 2.43 and 2.55. The extinction coefficient (k) is found between 0.4 and 0.7 which is similar to the widely reported value in its literature. It can therefore be inferred that: doping the material with boron modified/tuned atomic distribution of the ZnO thin films, causes changes in the optical properties. This could be useful in many areas including optoelectronics, solar cells, photo catalysis, single or multilayer optical coatings, and dye-sensitized solar cells.