Growth and characterization of nano-structured Sn doped ZnO

In the present investigation, we report the transparent and conducting Sn doped ZnO (Sn–ZnO) films fabricated by a chemical spray pyrolysis technique (CSPT). The effect of Sn concentration on the structural, morphological, electrical and optical properties has been studied. Contrary to the common observation, the optical band gap of Sn–ZnO is red-shifted from 3.26 to 2.98 eV as the dopant concentration was increased to 5 wt.% but remained at this value with a further increase in Sn percentage to 10 wt.% (2.96 eV). The red-shift of the optical band gap is due to the deep states in the band gap. The increase in density of states has been confirmed by variable range hoping (VRH) mechanism. The activation energy was found to be decreased when Sn concentration increased. The low temperature conduction has been explained by VRH mechanism, which fits very well in the temperature range 100–300 K. The optical property of Sn–ZnO system in terms of the band structure has been tentatively discussed.