Dangling bond defects in Si1−xGex alloy nanocrystals (nc-Si1−xGex) as small as 4 nm in diameter embedded in SiO2 thin films were studied by electron spin resonance (ESR), and the effects of the defects on photoluminescence (PL) properties were discussed. It was found that the ESR spectrum is a superposition of signals from Si and Ge dangling bonds at the interfaces between nc-Si1−xGex and SiO2 matrices (Si and Ge Pb centers). As the Ge concentration increased, the signal from the Ge Pb centers increased, while that from the Si Pb centers was nearly independent of Ge concentration. The increase in the number of Ge Pb centers was accompanied by strong quenching of the PL. The observed correlation between the two measurements suggests that the Ge Pb centers act as efficient nonradiative recombination centers for photogenerated carriers, resulting in the quenching of the main PL.

The effects of P doping on photoluminescence ͑PL͒ properties of Si 1Ϫx Ge x alloy nanocrystals (nc-Si 1Ϫx Ge x) in SiO 2 thin films were studied. P doping drastically decreases the electron spin resonance ͑ESR͒ signals that are assigned to the Si and Ge dangling bonds at the interfaces between nc-Si 1Ϫx Ge x and SiO 2 matrices ͑Si and Ge P b centers͒. 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 Si 1Ϫx Ge x alloy crystals can be controlled by impurity doping.

No abstract

No abstract

Dangling bond defects in Si1−xGex alloy nanocrystals (nc-Si1−xGex) as small as 4 nm in diameter embedded in SiO2 thin films were studied by electron spin resonance (ESR), and the effects of the defects on photoluminescence (PL) properties were discussed. It was found that the ESR spectrum is a superposition of signals from Si and Ge dangling bonds at the interfaces between nc-Si1−xGex and SiO2 matrices (Si and Ge Pb centers). As Ge concentration increased, the intensity of the signal from the Ge Pb centers increased, while that from the Si Pb centers was almost independent of Ge concentration. The increase in the number of Ge Pb centers was accompanied by strong quenching of the PL. The observed correlation between the two measurements suggests that Ge Pb centers act as efficient non-radiative recombination centers for photogenerated carriers, resulting in the quenching of the PL.