Optical and Electrical Characterization of Stable p-Type ZnO Thin Films Obtained by Bismuth Doping

We report the growth of stable p-type ZnO thin films obtained by doping bismuth (Bi) in ZnO and deposited over ITO coated glass substrate. The Bi doped ZnO thin films have been deposited by a sol-gel spin coating method using zinc acetate and bismuth nitrate as main precursors. The structural, optical and electrical properties of annealed Bi doped thin films have been studied in detail using X-ray diffraction (XRD), Atomic force microscopy (AFM), ellipsometry, hot probe system and Hall measurement. The presence of strong diffraction peak along (101) obtained from the XRD spectra shows that the high-quality Bi doped ZnO nanostructures grow along (101) orientation. A number of important micro-structural parameters for the thin films such as grain size, lattice parameters, stress and texture coefficient have been calculated, in order to show the effect of Bi incorporation in ZnO thin film. Further, transmittance has been calculated over the range of 350- 800 nm wavelength regions. The optical band gap of Bi doped ZnO films have also been calculated for different concentrations of Bi using the data taken by an ellipsometer. Hot probe characterization method has been used to ascertain the type of semiconductor thin film and it was observed that films doped with the concentration of 10 mol% Bi show p-type nature that was found to be stable over the period of eight months. Further, in order to calculate the resistivity, hole concentration, and mobility of p-type Bi doped ZnO thin film Hall measurement have been performed.