Effect of Nb doping on structural, electrical and optical properties of spray deposited SnO2 thin films

Abstract

Nb doped SnO2 transparent conducting thin films were deposited by spray pyrolysis method. Microstructural, morphological, electrical and optical properties of the films were investigated as a function of niobium (Nb) doping, in the range from 1.0% to 4.0% by atomic percent (with 1.0 at.% step). From XRD patterns the films exhibited a tetragonal cassiterite structure. Although (2 1 1) peak is the most intense peak which is observed for all samples, the (3 0 1) reflection has the highest texture coefficient. The grain size values for (2 1 1) and (3 0 1) peaks were dependent on Nb doping concentration and they varied in the range of 34.99-24.15 nm and 131.4-216.7 nm, respectively. The SEM images of the films showed that the films were made up of grains with polyhedron like shape and that smaller grains were mostly seen in the spaces between polyhedron like grains. Also, SnO2 thin film doped with 2.0 at.% Nb exhibited lowest values of sheet resistance (6.84 Omega) and resistivity (0.62 x 10(-3) Omega cm), beside the highest value of figure of merit (3.4 x 10(-3) Omega(-1)) was obtained for 1.0 at.% Nb doped thin film. The direct optical band gap decreased from 3.98 eV to 3.73 eV with increasing Nb concentration. These results make Nb doped SnO2 films an attractive candidate for many optoelectronic applications.