Synthesis and size control of Si nanocrystals by SiO/SiO 2 superlattices and Er doping

The synthesis of nc-Si by reactive evaporation of SiO and subsequent thermal induced phase separation is reported. The size control of nc-Si is realized by evaporation of SiO/SiO 2 superlattices. By this method an independent control of crystal size and density is possible. The phase separation of SiO into SiO 2 and nc-Si in the limit of ultrathin layers is investigated. Different steps of this phase separation are characterized by photoluminescence, infrared absorption and transmission electron microscopy measurements. The strong room temperature luminescence of nc-Si shows a strong blueshift of the photoluminescence signal from 850 to 750 nm with decreasing crystal size. Several size dependent properties of this luminescence signal, like decreasing radiative lifetime and increasing no-phonon transition properties with decreasing crystal size are in good agreement with the quantum confinement model. Er doping of the nc-Si shows an enhancement of the Er luminescence at 1.54 μm by a factor of 5000 compared to doped SiO 2 layers. The decreasing transfer time for the nc-Si to Er transition with decreasing crystal size can be understood as additional proof of increasing recombination probability within the nc-Si for decreasing crystal size.