Influence of thickness and annealing temperature on the electrical, optical and structural properties of AZO thin films

Transparent conductive Al-doped ZnO (AZO) thin films with various thicknesses between 520 and 1420 nm were deposited on quartz substrates by radio frequency (RF) magnetron sputtering at room temperature for thin film solar cells as transparent conductive oxide (TCO) electrode layers. After deposition, the samples were annealed in a vacuum ambient at temperatures between 250 and 550 °C for a period of 30 min. The structural, electrical, and optical properties of these films have been analyzed as a function of the thickness and the annealing temperature by a series of characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Hall effect measurements and spectrophotometry. All of these samples exhibited strong (002) diffraction peaks and the visible range transmittance was over 80%. In addition, with the increase of thickness, the Hall mobility increased from 4.88 to 7.86 cm2/V, the resistivity decreased from 1.2 × 10−2 Ω cm to 4.2 × 10−3 Ω cm. Annealing in vacuum improved the crystallinity together with some changes of the electrical resistance that depended on the annealing temperature. The best characteristics have been obtained at 450 °C, where the lowest resistivity was 2.7 × 10−3 Ω cm for the thickest films.