Effects of P doping on photoluminescence of Si1-xGex alloy nanocrystals embedded in SiO2 matrices:: Improvement and degradation of luminescence efficiency

The effects of P doping on photoluminescence (PL) properties of Si1-xGex alloy nanocrystals (nc-Si1-xGex) in SiO2 thin films were studied. P doping drastically decreases the electron spin resonance (ESR) signals that are assigned to the Si and Ge dangling bonds at the interfaces between nc-Si1-xGex and SiO2 matrices (Si and Ge P-b centers). With increasing P concentration, the signal from the Ge P-b centers are first quenched, and then the signal from the Si P-b centers start to be quenched. The quenching of the ESR signals is accompanied by a drastic enhancement of the PL intensity. The PL intensity has a maximum at a certain P concentration, which depends on the Si:Ge ratio. By further increasing the P concentration, the PL intensity becomes weaker. In this P concentration range, optical absorption emerges due to the intravalley transition of free electrons generated by the P doping. The observation of the free-electron absorption provides direct evidence that carriers in nanometer-sized Si1-xGex alloy crystals can be controlled by impurity doping. (C) 2001 American Institute of Physics.