Optical properties of silicon micro and nanocrystals

Abstract

Silicon nanocrystal aggregates have been produced in an inert argon gas by a pulsed laser vaporization-condensation technique using the second harmonic of a Nd: YAG laser. In our previous work, it has been shown that materials generated by evaporation-condensation technique present a variety of structures depending on the conditions of production. A theoretical model has been elaborated from a multitude of metallic samples, taking into consideration the effect of the main physical factors on the resulting morphology. This model has been applied to silicon in order to produce silicon nanocrystals with specific structural characteristics. We carried out an investigation of the influence of the structure on the optical properties of silicon nanocrystals. In this report, we present the first results from this investigation. We have explored the inert gas pressure variation effect on the resulting nanocrystallite structures. Investigation under scanning electron microscopy (SEM) has revealed a weblike arrangement whose density gradually increases with the value of pressure. The deposits have been exposed to ambient air for eight months before photoluminescence (PL) measurements. The oxidized nanocrystals exhibited PL and the broad bands seem composed of multiple narrower bands. Silicon nanocrystals are the best candidates for the understanding of the extended red emission (ERE) visible in spectroscopic observations of many astronomical objects.