A combined theoretical and experimental study on vertically aligned ZnO and ZnO: Sn

Vertically aligned ZnO and Sn (5, 10 v/v%) doped ZnO microrods were produced using chemical bath deposition technique on ZnO seed layers fabricated on glass substrates by spin coating method. The thickness of the seed layer is 365 nm and the length of the ZnO and ZnO:Sn rods are in the range of 1-5 mu m. The length of the rods decreases with increasing Sn concentration. The structural, morphological, elemental compound, electrical and optical properties of ZnO and ZnO:Sn films were investigated using x-ray powder diffraction, field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy, two probe method and UV-Vis absorption spectroscopy, respectively. The electronic structure of ZnO and Sn doped ZnO is calculated depending Density Functional Theory thanks to the WIEN2k program. Based on experimental and theoretical calculations, the band gap energy decreases with increasing Sn concentration. The band gap energy of seed layer, pure ZnO, Sn (5%) and Sn (10%) doped ZnO films was estimated as 3.27 eV, 3.18 eV, 3.14 eV and 3.12 eV, respectively. The band gap energy of Sn (1 atom) and Sn (2 atom) doped ZnO calculated theoretically was found as 0.392 eV and 0.245 eV, respectively. The Fermi Energy shifting towards the conduction band was observed upon Sn doping. Sn (5%) doped ZnO film shows the highest electrical conductivity although its band gap energy is higher than that of Sn (10%). The highest conductivity is attributed to the lowest dislocation density and less oxygen vacancies in the structure.