Optimizing growth parameters for highly luminescent Er:Al2O3 thin films that act as a base to fabricate a PT laser

Abstract

Recently PT symmetric devices, a new class of artificial optical materials, found a tremendous interest in research where PT symmetry is maintained by balancing gain and loss regions, and therefore combined PT operation leads to interchange loss and gain and leaves the system invariant. Based on this gain/loss modulation concept, we demonstrate both experimentally and theoretically a PT symmetric laser fabricated out of a grating structure on the top surface of erbium doped alumina thin films deposited by Co-sputtering technique. Erbium doped in alumina act as one of the best choice to fabricate such an active device because Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> effectively improves the erbium ion doping concentration and hence increasing fluorescence lifetime giving a large optical gain in a smaller device size. In order to fabricate such grating structure, firstly we have optimized the growth parameters for depositing homogeneous and highly luminescent Er:Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thin films on thermally oxidized silicon substrates. The main subject of investigation includes the effect of change in various deposition parameters like substrate heating, RF power and oxygen pressure inside the chamber while deposition. Co-sputtering is found to be very promising technique for fabrication of such films as CVD and sol-gel techniques suffer from the presence of hydroxyl groups that incorporates inside the film during deposition and that induce luminescence quenching. In this paper, high quality as-deposited films with various Er concentrations and low carbon contents have been confirmed by XPS. Substrate heating ~ 500°C was found to be very effective in getting highly dense films with high refractive index of 1.70 in 1530-1565nm band. The films showed highly intense PL peak at 1550nm even without any post deposition annealing treatment.