Optimization of the optical properties of Er-doped Si-rich SiO2/SiO2 multilayers obtained by reactive magnetron sputtering

The effects of annealing time and of Si nanocluster (Si-nc) size on the coupling rate to Er ions were investigated through studies made on multilayers (MLs) consisting in about 20 periods of Er-doped Si-rich SiO2/SiO2. These MLs were deposited by reactive magnetron sputtering at 650 °C and subsequently annealed at 900 °C. A steep increase of the PL emission is observed for short annealing time while a trend of some saturation occurs for longer treatment time. Besides, the Er lifetime continuously increases with the annealing time. For Si-rich layer thickness or Si-nc larger than about 5 nm, the rate of energy transfer is lowered because of the weak confinement of carriers and the loss of resonant excitation of Er through the upper levels (second, third, etc.). The latter is liable to prevent the energy back transfer process, while the weak confinement reduces strongly the probability of no phonon radiative recombination that governs the transfer excitation rate from Si-nc to Er ions.