Ultrasonic spray pyrolyzed copper oxide and copper-aluminum oxide thin films: optical, structural and electronic properties

摘要： A study of the structural, electrical and optical properties of copper oxide and copper-aluminum oxide thin films deposited by ultrasonic spray pyrolysis is presented in this work. On one hand copper oxide films were deposited at working temperatures in the range from 300 °C to 500 °C. These films present a mixture of Cu2O and CuO phases, CuO phase being more abundant at higher temperatures; all samples present p-type conductivity. On the other hand, copper-aluminum oxide samples were deposited at 350 °C but with different copper-aluminum ratios in the start solution (0, 12.5, 25, 50, 100, and 200 at.%). The films present a mixture of Cu2O and Al2O3 phases, being the Cu2O the most abundant and becoming amorphous as aluminum concentration rises. Electrical characterization indicates that electronic conductivity depends on the amount of Cu2O, while ionic conductivity increases with aluminum concentration. Aluminum concentration also provokes a shift in the valence band towards lower binding energies, as well as an increase in the optical band gap (from 2.6 to 3.7 eV). Upon a thermal annealing at 800 °C the samples turned to CuAl2O4 spinel structure.