Dependence of structural, electrical, and optical properties of ZnO:Al films on substrate temperature

ZnO:Al (ZAO) films were deposited on fused silica substrates heated to 350 °C by dc magnetron reactive sputtering from a Zn target mixed with 1.5 wt% Al. Films deposited on a substrate heated to a temperature between room temperature and 300 °C were (001)-oriented crystals, but those grown at 350 °C consisted of crystallites with (001) and (101) orientations. The dependence of electrical properties such as resistivity, carrier concentration, and Hall mobility on temperature was measured. The results indicate that the carrier concentration and Hall mobility increase with increasing temperature up to 250 °C, though the Al content remains unchanged in this temperature range. The probable mechanisms are discussed. The minimum resistivity of ZAO films is 4.23 × 10⁻⁴ Ω cm, with a carrier concentration of 9.21 × 10²⁰ cm⁻³ and a Hall mobility of 16.0 cm² v⁻¹ s⁻¹. The films show a visible transmittance of above 80%.