Structural, Optical, and Electrical Properties of Nb-Doped ZnO Thin Films Prepared by Spray Pyrolysis Method

Niobium (Nb) doping (0 at.% to 3 at.%) in ZnO thin films prepared by the chemical spray pyrolysis method at a substrate temperature of 400°C enhances the optical and electrical properties but deteriorates the structural quality of the films. The films are polycrystalline with hexagonal structure having a preferential orientation along the (002) crystallographic direction. The film doped with 3 at.% Nb demonstrates a maximum average transmittance of ~83% in the visible region. A strong blue emission is recorded for both pure and doped films, and the intensity is substantially enhanced with Nb doping due to interface and valence-band transitions. Vacuum annealing at 400°C for 60 min improves the electrical characteristics of the films, and the highest mobility of 71 cm2/V s is achieved for the 1 at.% Nb-doped ZnO films.