The structural and optoelectronic properties of Ti-doped ZnO thin films prepared by introducing a Cr buffer layer and post-annealing

Abstract

This work investigates the effects of Cr buffer layers and post- annealing on the properties of titaniumdoped zinc oxide (TZO) thin films prepared by radio frequency magnetron sputter. All films had a (0 0 2) preferential orientation along the c-axis at 2 theta similar to 34 degrees. The crystallinity, grain size, Hall mobility and carrier concentration of TZO films were enhanced by introducing a Cr buffer layer and post-annealing. The decrease in resistivity was mainly attributed to the increase in Hall mobility rather than carrier concentration. As a Cr buffer layer was inserted, the film resistivity decreased by 32% to 5.41 x 10(-3) Omega cm while the energy band gap increased from 3.252 to 3.291 eV in comparison with that of the film deposited without the buffer layer. When the Cr-buffered films were annealed in a vacuum, the structural, electrical, and optical properties were improved with increasing annealing temperature. At an annealing temperature of 500 degrees C, the grain size, resistivity, and energy band gap attained the optimal values of 28.12 nm, 3.37 x 10(-3) Omega cm and 3.357 eV, respectively. The average transmittance of TZO films in the visible region was between 75% and 84%, and it decreased with increase in the grain size. The decrease in transmittance is attributed to an increase in surface roughness due to the three-dimensional island grain growth during thermal annealing. (c) 2012 Elsevier B.V. All rights reserved.