Electronic And Dielectric Properties Of Porous Silicon

Abstract

Bulk Si is, due to its indirect band-gap electronic structure, a very inefficient emitter, even at liquid He temperatures. In recent years several approaches were developed towards improving the efficiency of light emission from Si-based structures. All of them were based on the lifting of the lattice periodicity inducing an uncertainty in the k-space and therefore altering the indirect nature of this material. Additionally, a better overlap of wavefunctions of electrons and holes results in a larger oscillator strength of optical transitions. Some examples are: SiGe [1] or Si-SiO₂ superlattices [2] or Si nanocrystal assemblies [3]. The largest quantum yield that has been achieved under optical excitation of Si nanocrystals is of the order of 10% and is already comparable with that of direct band-gap quantum dots assemblies. The purpose of the paper is to survey the experimental work which has been carried out towards detailed understanding of the basic optical properties of silicon nanocrystal assemblies.