Effect of SnO2 concentration on the tuning of optical and electrical properties of ZnO-SnO2 composite thin films

Abstract

ZnO-SnO2 composite thin films have been deposited at 400 °C on glass substrates using targets of different SnO2 content (1 to 40 wt. %) by pulsed laser deposition technique. The structural, optical, and electrical properties of the composite films have been studied as a function of SnO2 content. It is revealed from X-ray diffraction analysis that films are crystalline in nature and the crystallite size decreases from 20–23 nm to 5–7 nm with increase of SnO2 content. X-ray photoelectron spectroscopy analysis indicates that Sn is predominantly doped into the ZnO lattice upto a SnO2 content of 15 wt. % in the composite. For higher concentration, a separate SnO2 phase is segregated in the composite. The band gap energy as well as the electrical conductivity can be tuned by varying the SnO2 content in the composite. Low temperature electrical conductivity measurements show three dominant conduction mechanisms in the temperature range of 20–300 K. At high temperature range of 200–300 K, thermal activation conduction process is dominant. Nearest neighbor hopping conduction mechanism, which occurs in the shallow impurity bands, is dominant in the temperature range of 90–200 K. In the low temperature range of 20–90 K, the electronic transport occurs through Mott's variable range hopping conduction process.