Study on the zinc doping and annealing effects of sprayed In2O3 thin films

Abstract

Zinc doped indium oxide thin films (In2O3:Zn) have been successfully prepared on glass substrates using spray pyrolysis technique for different zinc concentrations y $$\big( {{\text{y}} = \frac{{[{\text{Zn}}^{2 + } ]}}{{[{\text{In}}^{3 + } ]}} = \, 0,1, \, 2, \, 3, \, 4, \, 5\;{\text{and}}\,6\,{\text{at}}.\% } \big)$$ . The structure, surface morphology, optical and electrical properties of In2O3:Zn thin films were investigated by X-ray diffraction, atomic force microscopy, spectrophotometer, fluorescence spectrometer and Hall Effect. It is found that physical properties of In2O3 material are affected by doping with zinc element. Structural analysis shows that In2O3 thin layers are polycrystalline with cubic structure. After doping, a double transition of preferential orientation was observed from (222) to (400) for y = 1 at.% and from (400) to (440) for y = 3 at.%. The best crystallinity is obtained for y = 1 at.% with (400) as a preferred orientation. The maximum grain size is obtained for y equals to 1 at.%. Optical transmission shows an average value after doping of about 80 % with interference fringes revealing the good uniformity and homogeneity of deposited layers. After doping, the direct band gap Eg is equals to 3.51 eV for In2O3:Zn (1 at.%). The single oscillator energy E0 and dispersion energy Ed were determined by Wemple model using the envelope method. We obtained E0 = 2 × Eg for doped films. Electrical resistivity (ρ) decreases from 650.20 × 10−3 to 198.50 × 10−3 Ω cm for respectively undoped and In2O3:Zn (1 at.%). A heat treatment under nitrogen atmosphere of In2O3:Zn (1 at.%) thin films leads to enhanced optical transmission especially for 250 (2 h) and 450 °C (2 h). A significant decrease of the resistivity to about 2.82 × 10−3 Ω cm is obtained for annealing temperature equals to 250 °C (2 h). All these experimental results lead to consider that annealed zinc doped indium oxide thin films can be used as transparent conductive oxide material in optoelectronic applications.