Effect of Al content on electrical conductivity and transparency of P-type Cu-Al-O thin film

Copper aluminum oxide (Cu-Al-O) film was prepared by radio-frequency (RF) sputter method using a pure metal Cu target and a mosaic target with different relation between Al and Cu at room temperature, respectively. The effects of Al content on crystal structure, electrical conductivity, and optical transmittance were studied. The composition of the film was adjusted by placing various numbers of Cu disks on the Al target surface. The Al concentration in the films were measured as 0, 4.2, 6.8, and 20.5 at.%, respectively. As the Al content in the deposited films increased, the crystal structure changed from CuO to amorphous CuAlO2 and the resistivity of the deposited films increased. The resistivity of Cu-Al-O films obtained in this study ranged from 0.5 Ω-cm to 4.8 MΩ. The increased resistivity can be attributed to the incorporated Al3+ ions substituting the Cu2+ ions, thus decreasing the hole concentration. The average optical transmittances in the visible range (400–800 nm) of the deposited films were measured as 20.1%, 33%, 43.9%, and 73.9 % and the related optical band gaps obtained from optical transmittances were 2.1, 2.6, 2.7, and 2.9 eV, respectively.