Influence of thallium doping on structural, electrical, and optical properties of ZnO nanorods for TCO applications

Thallium (Tl)-doped ZnO nanorods were prepared (the doping ratios were between 0 and 5 mol %) in two stages. Combined sol-gel and spin-coating methods and hydrothermal method were used, respectively. Depending on the concentrations of the Tl dopant, the structural, morphological, electrical, and optical properties of the samples were examined. XRD results demonstrated that the ZnO samples were in hexagonal (wurtzite) unit cell type with single crystalline nature. FE-SEM results indicated that the undoped and Tl-doped ZnO samples had hexagonal rod-like structures. The average lengths and diameters of the samples were between 0.90 and 1.35 mu m, and 80 and 120 nm, respectively. The electrical conductivity increased with increasing temperature and doping concentrations. For the undoped and 5 mol % Tl-doped ZnO-samples, the electrical conductivity values were 1.22E-08 and 1.95E-05 (omega.cm)(-1) at 25 degrees C and 4.84E-07 and 3.97E-04 (omega.cm)(-1) at 300 degrees C, respectively. The 1 mol % Tl-doped ZnO had the highest transmittance (within the range of 70 and 80%) in the wavelength of between 500 and 1000 nm. The band gap energy values of the Tl-doped samples were higher than the undoped ZnO sample.