Development of phase-pure CuAlO2 thin films grown on c-plane sapphire substrates prepared by RF sputtering

Abstract CuAlO 2 films were deposited on c-plane sapphire by radio-frequency (RF) reactive sputtering using a CuAlO 2 ceramic target at different deposition temperatures. The as-deposited films were found to be amorphous regardless of the deposition temperatures. After annealing at 1050 °C in air, only the film deposited at 700 °C showed the crystalline CuAlO 2 structure but with a small amount of CuAl 2 O 4 impurity. During post-annealing, Al in the sapphire substrate reacted with the as-deposited Cu–Al–O film so the whole film contained excess of Al, leading to the formation of CuAl 2 O 4 . To suppress CuAl 2 O 4 , a layer of 100 nm Cu 2 O film was deposited between the Cu–Al–O film and sapphire. In the annealing process, Cu 2 O reacted with sapphire to form CuAlO 2 so the ratio of Cu to Al of the whole film was maintained, and a highly preferred c-oriented CuAlO 2 film without impurity was fabricated. The room temperature electric conductivity of the phase-pure CuAlO 2 thin film is 1.01 S cm −1 , which is two orders of magnitude better than that of the film with CuAl 2 O 4 impurity. The CuAlO 2 film exhibited both p-type conductivity and transparency in the visible region.