Electron spin resonance study of defects in Si1-xGex alloy nanocrystals embedded in SiO2 matrices: Mechanism of luminescence quenching

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 s pin resonance (ESR), and the effects of the defects on photoluminescence (P L) properties were discussed. It was found that the ESR spectrum is a super position of signals from Si and Ge dangling bonds at the interfaces between nc-Si1-xGex and SiO2 matrices (Si and Ge P-b centers). As the Ge concentra tion increased, the signal from the Ge P-b centers increased, while that fr om the Si P-b centers was nearly independent of Ge concentration. The incre ase in the number of Ge P-b centers was accompanied by strong quenching of the PL. The observed correlation between the two measurements suggests that the Ge P-b centers act as efficient nonradiative recombination centers for photogenerated carriers, resulting in the quenching of the main PL. (C) 20 01 American Institute of Physics.