Transport Properties of As-Prepared Al-Doped Zinc Oxide Films Using Sol–Gel Method

ZnO films doped with different concentrations of aluminum (AZO) have been prepared by the sol–gel technique. The electrical properties of the samples have been measured on as-deposited films. Two of the films have been heat treated in vacuum at 400 °C to determine the changes in transport properties. The electrical properties, i.e. conductivity and Hall coefficient, have been studied from room temperature down to low temperatures. Combining these two it has been possible to determine the Hall mobilities, carrier concentrations and the barrier height at the grain-boundary region. Attempts have been made to explain the barrier height assuming monovalent trapping states at the grain boundary and the density of trapped states has been estimated from the experimental data. As carrier concentration increases after heat treatment of the samples in vacuum the role of non-ionized impurities decreases.