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

• Published in: Applied surface science 2012-10, Vol.258 (24), p.9891-9895
• Main Authors: Lin, Y.C., Hsu, C.Y., Hung, S.K., Chang, C.H., Wen, D.C.
• Format: Article
• Language: English
• Subjects: Annealing; Buffer layer; Buffer layers; Carrier density; Chromium; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Electrical resistivity; Electron mobility; Exact sciences and technology; Hall effect; Magnetron sputtering; Physics; Post-annealing; Thin films; Ti-doped ZnO; Transmittance; Zinc oxide
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2012.06.046

► The effects of buffer layer and annealing on properties of TZO films were studied. ► All films exhibited strong (002) diffraction peaks of hexagonal structure. ► The buffered TZO films had lower resistivity and higher energy band gap. ► The decrease in resistivity was mainly attributed to increase in Hall mobility. ► Optimal electrical and optical properties were obtained after annealing at 500°C. This work investigates the effects of Cr buffer layers and post-annealing on the properties of titanium-doped zinc oxide (TZO) thin films prepared by radio frequency magnetron sputter. All films had a (002) preferential orientation along the c-axis at 2θ∼34°. 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 5.41×10−3Ωcm while the energy band gap increased from 3.252 to 3.291eV 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°C, the grain size, resistivity, and energy band gap attained the optimal values of 28.12nm, 3.37×10−3Ωcm and 3.357eV, 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.