Structural and optoelectronic properties of p-type semiconductor CuAlO2 thin films

This study investigates the structural and optoelectronic properties of p-type CuAlO2 films. The films were prepared through magnetron sputtering deposition and underwent annealing in a controlled Ar atmosphere at 800 °C with different holding times. This temperature ensures that the formation of the CuAlO2 phase is favored. As the holding time for annealing increases, diffusion of copper, aluminum and oxygen atoms contributes to the phase change and grain growth of CuAlO2. CuO, Al2O3 and CuAl2O4 exist as reaction intermediates, but their proportion of the sample is reduced to zero during the formation of CuAlO2. No interface compound was found as a byproduct on the quartz substrate and CuAlO2 film due to the high-temperature annealing. The single-phase CuAlO2 films had root mean square roughness of 3.98 nm. The average CuAlO2 grain size increased from 33.70 to 35.43 nm after 4 and 5 h of annealing, respectively. The increased grain size is concurrent with a decrease of the band gap of the CuAlO2 film. Single-phase p-type CuAlO2 films showed lower electrical resistivities of 231.9 and 242.5 Ω cm, with direct band gaps of 3.33 and 3.26 eV, respectively.

► The CuO, Al2O3 and CuAl2O4 are intermediate phases for the formation of CuAlO2.
► To promote the CuAlO2 formation, we increase the annealing holding time at 800 °C.
► The grain size has a big influence on the band gap of single-phase CuAlO2 film.
► The lowest resistivity of CuAlO2 film is 231.9 Ω cm, with a band gap of 3.33 eV.
► The CuAlO2 dominates the structural and optoelectronic properties of these films.