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

Abstract

CuAlO x thin films were prepared at three substrate temperatures (TS=60, 300, and 600 °C) and two oxygen partial pressures (PO2=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 PO2=0.5 mTorr were oxygen deficient; although the delafossite structure formed upon annealing, electrical properties were poor. Films deposited with PO2=2 mTorr transformed into the delafossite structure and exhibited p-type conductivity after annealing under N2 at temperatures TA≥750 °C. Conductivity generally increased with increasing TS and decreasing TA. A special case of PO2=2 mTorr and low TS (60 °C) resulted in a partially crystalline oxide phase that transformed into the delafossite structure at TA=700 °C and yielded the highest conductivity of 1.8 S cm−1. In general, a TA 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.