Photoluminescence properties of silicon nanocrystals as a function of their size

We present results on the photoluminescence (PL) properties of silicon nano crystals as a function of their size. The nanocrystals are synthesized by l aser pyrolysis of silane in a gas flow reactor and deposited at low energy on a substrate after a mechanical velocity and size selection. Both the pho toluminescence spectroscopy and yield have been studied as well as the effe ct of aging of the samples in air. The measurements show that the PL of the silicon nanocrystallites follows the quantum confinement model very closel y. The apparent PL yields are rather high (up to 18%). From evaluation of t he size distribution obtained by atomic force microscopy it is concluded th at the intrinsic PL yield of the nanocrystals can reach almost 100%. These results enabled us to develop a simple theoretical model to describe the FL of silicon nanocrystals. This model can also explain the changes of PL wit h aging of the sample, just by invoking a decrease of the size of the cryst alline core as a result of oxidation.