Effect of substrate temperature on structural and electrical properties of K-doped p-ZnO thin films

ZnO thin films have been deposited on (0001) sapphire substrates using potassium (K) as a dopant by radio frequency magnetron sputtering technique. The electrical properties, crystallinity and surface morphology of as-grown ZnO films are investigated by Hall measurement, X-ray diffraction and Atom Force Microscopy. Results show that the structure and electrical properties of p-K:ZnO films are strongly dependent on the substrate temperature. From 300 to 700°, all K-doped ZnO samples prepared under rich oxygen atmosphere possess p type conductivity, and the best results are obtained at 500° with the hole carrier concentration, resistivity and hole mobility of typical 3.19×1017 cm−3, 10.7 Ω.cm, and 1.83 cm2/V.s, respectively. At the same temperature, the p-K:ZnO films also exhibit the best surface quality with the strongest intensity of (101) diffraction peak, and the preferred orientation (002) peak becomes too weak to be observed. The surface morphology is also smoother and uniform with the average roughness of 105.7 nm and grain size of 231.3 nm.