PLD growth of CuAlO2

Copper aluminium oxide, CuAlO2 (“CAO”) films were deposited by pulsed laser deposition (“PLD”) on a variety of substrates. As-deposited films were X-ray amorphous. Films formed at 200 °C were insulating, whereas films formed on sapphire at 720 °C were conducting. Specific conductivity and light transmittance were optimized for CAO/sapphire. Best values for the conductivity of around 0.3 S/cm for 280 nm thick films on sapphire were obtained for 3.5 J/cm2/pulse, substrate to target distance 6.5 cm, 400 mTorr oxygen and 720 °C, deposition time 90 min at 10 Hz. Films obtained under these conditions were specular and had a refractive index around 2.1 as derived from reflectivity measurements. Transmission spectra showed an onset around 400 nm and a non-negligible unspecific absorption above.Annealing of as-deposited, X-ray amorphous films on sapphire at 1050 °C in air for 5 min led to crystallization in combination with disruption of film continuity (and therefore loss of conductivity) as seen by optical microscopy, where hexagonal platelets could be clearly distinguished. X-ray analysis showed highly preferential orientation (<003>, <006>, <009>, <0012>). Post-annealing in situ (15 min–8 h) at 720 °C had no effect on film properties.