DC reactive magnetron sputtering, annealing, and characterization of CuAlO2 thin films

CuAlOx thin films were prepared at three substrate temperatures (T-S=60, 300, and 600 degrees C) and two oxygen partial pressures (P-O2=0.5 and 2 mTorr) via dc reactive magnetron sputtering from Cu-Al 50-50 at. % alloy targets and subsequent annealing. As-deposited films with P-O2=0.5 mTorr were oxygen deficient; although the delafossite structure formed upon annealing, electrical properties were poor. Films deposited with P-O2=2 mTorr transformed into the delafossite structure and exhibited p-type conductivity after annealing under N-2 at temperatures T-A >= 750 degrees C. Conductivity generally increased with increasing T-S and decreasing T-A. A special case of P-O2=2 mTorr and low T-S (60 degrees C) resulted in a partially crystalline oxide phase that transformed into the delafossite structure at T-A=700 degrees C and yielded the highest conductivity of 1.8 S cm(-1). In general, a T-A near the phase formation boundary led to an increase in conductivity. Low-temperature hydrothermal annealing was also investigated and shown to produce mixed phase films exhibiting the delafossite structure along with CuO, AlOOH, and Al2O3. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3525640]