Deposition of Ti:sapphire thin films by reactive pulsed laser ablation using liquid metals and oxygen

Ti:sapphire films were grown using molten Al-Ti alloy ablation targets with either O-2 gas pulses or O-2 background reactive medium on sapphire (0001) substrates. The films were characterized by the use of XRD, RHEED, AFM, and XPS. While the films deposited at a substrate temperature of 650 degrees C showed three-dimensional epitaxial growth, the films deposited at 1000 degrees C exhibited a two-dimensional structure. Annealing of the low-temperature deposited films improved the crystal quality but failed to improve the surface morphology. Ti exists in the host sapphire lattice in the form of Ti3+ for films deposited at lower temperatures, whereas it assumes the tetravalent form in the high-temperature deposited films. The valence states of Ti identified by XPS studies are in agreement with low-temperature luminescence results.