In this study, amorphous Cu-Al-O films were deposited onto a (100) p-type silicon substrate by a magnetron sputtering system. The films were then annealed at 700 degrees C and 800 degrees C for 2 h in N-2, air and O-2. X-ray diffraction patterns showed that the as-deposited films were amorphous. When the films were annealed at 700 degrees C, the monoclinic-CuO and spinel-CuAl2O4 phases were detected in all atmospheres. As the annealing temperature increased to 800 degrees C, delafossite-CuAlO2 (R 3m and P6(3)/mmc phases) appeared in N-2 whereas monoclinic-CuO and spinel-CuAl2O4 phases were detected in air and O-2. Thermodynamic calculations can explain the formation of delafossite-CuAlO2 films. The optical bandgap and conductivity of delafossite-CuAlO2 films were 3.30 eV and 6.8 x 10(-3) S/cm, respectively:which are compatible with other data in the literature. The p-type characteristic in delafossite-CuAlO2 films was verified by a hot-probe method. (C) 2011 Elsevier B.V. All rights reserved.