Characterisation of Ti:sapphire layers synthesized energy ion implantation

High energy ion implantation has been investigated as a means of locally doping sapphire with Ti to form Ti:sapphire: a highly valued laser material. We have characterised the properties of Ti:sapphire layers formed by this process over a wide range of ion implantation and thermal processing conditions in order to understand the mechanisms which lead to stabilisation of Ti in the required optically-active 3+ chemical state. Characterisation by a wide variety of techniques including photoluminescence (PL) and luminescence lifetime has been used to provide a detailed picture of the annealing behaviour of the ion implanted layers and the dependence of formation of Ti³⁺ on the implantation conditions, annealing ambient and temperature. For annealing below about 1300°C, the Ti can be encouraged to form the 3+ state by co-implanting O into the substrates. For anneals above 1300 °C, the annealing ambient plays a dominant role with a reducing environment producing the highest Ti³⁺ PL output and co-implantation no longer being helpful. In this regime, the Ti³⁺ luminescence yield increases rapidly with increasing temperature and the lifetime approaches that of bulk Ti:sapphire. The Ti also begins to diffuse substantially. We have also observed a substrate orientation dependence to the Ti³⁺ formation. Implantation into a-axis oriented substrates results in a substantial improvement in the luminescence yield: an effect which is greater than the orientation-dependence of the absorption cross-section and suggests that damage recovery and activation of the Ti may be better in a-axis oriented sapphire.