Influence of annealing temperature on properties of room-temperature rf-sputtered CuAlOx:Ca thin films

The influence of annealing temperature on the characteristics of rf-sputtered CuAlOx:Ca thin films is studied. Room-temperature sputter-deposited CuAlOx:Ca thin films show an amorphous/nanocrystalline phase with p-type conductivity, as evidenced by Hall measurements and Seebeck coefficient measurements. This film becomes slightly crystalline after annealing at 600 °C for 5 h in N2 atmosphere. As the annealing temperature is increased to 900 °C, crystalline CuAlO2 mixed with CuO and CaAl4O7 are formed in the film; these precipitates extrude and roughen the surface. ZnO:Al/CuAlOx:Ca diodes fabricated using CuAlOx:Ca films that are as-deposited or annealed at 600 °C show good rectification characteristics, whereas those fabricated using CuAlOx:Ca films annealed at 900 °C show poor diode performance owing to the rugged surface that leads to the poor interface and current leakage paths.