Nonradiative recombination processes in nanocrystalline silicon

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It is well known that nanocrystalline Si shows large photoluminescence quantum efficiency. The silicon nanocrystallites prepared by pulsed laser ablation method are a promising material since the size and surface condition can be controlled by deposition parameters. We also prepared nanoscale Si in SiO2 matrix or SiH2 matrix by RF sputtering methods. The photoluminescence(PL)properties of these materials. The PL peak energy of nc-Si prepared by PLA varied from 1.7 eV to 2.0 eV.In previous works, some authors concluded that the shift is originated to be quantum size effect. We found that the this peak is a super position of 1.7 ev and 2.0 ev peaks.The PL feature of nc-Si prepared by PLA was similar to that of nanoscale Si in SiO2 matrix or SiH2 matrix prepared by RF sputtering. Temperature quenching of the PL intensity reduced by alloying and resulted in the large PL intensity at room temperature. We could not observe a correlation between PL intensity and defect density. Nonradiative recombination processes in the alloys were discussed in terms of temperature dependence of PL intensity. We concluded bandgap fluctuation induced by alloying reduced a transition to the nonradiative defect center in these systems. Although the PL center of the a-Si alloy and Si nanocrystallites may different, the origin of the large PL efficiency should be similar in a viewpoint of nonradiative recombination.