Improvement in the luminescence properties of Si/CaF2 nanostructures

We report on the photoluminescence quantum efficiency and the lifetime of t wo Si/CaF2 heterostructures grown by molecular beam epitaxy. The first is a nanocrystalline Si/CaF2 multiquantum well which consists of interacting Si nanocrystallites within Si layers, the second is an annealed Si/CaF2 multi quantum well which can be described as a collection of non-interacting Si n anocrystallites embedded in the CaF2 matrix. While a photoluminescence effi ciency of 0.01% has been found in the former, it reaches 1% in the latter. The energy dependence of the PL lifetime differs drastically between both s ets of samples. These results are explained in terms of carrier localizatio n. (C) 2000 Elsevier Science S.A. All rights reserved.