Optical characterization and photoluminescence study of porous silicon

I present a study of the optical properties of porous silicon using micro-Raman, micro-photoluminescence and FTIR spectrocopies. Porous silicon is grown by anodizing crystalline silicon in a hydrofluoric (HF) acid bath. The optical properties of this material are unique in that it luminesces strongly in the visible region. The origin of this luminescence is not fully understood and it is the goal of this paper to give some insight into this luminescence.; The first part of the research deals with understanding the crystalline phase of the porous silicon material. Micro-Raman measurements were performed on this material and were fit to a theoretical model for microcrystalline silicon ({dollar}mu{dollar}-Si) and amorphous silicon (a-Si). The results indicated that the porous silicon samples consisted of a combination of {dollar}mu{dollar}-Si and a-Si. The importance of the study was the indication that including the amorphous phase was necessary to extract the crystalline phase using Raman Spectroscopy.; The rest of the research was dedicated to photoluminescence (PL) of the porous silicon material. Micro-PL was used to achieve high laser power densities at the surface and monitor the evolution of the PL for both fast ({dollar}mu{dollar}sec) and slow (min) time periods. These results seem to indicate that carrier diffusion through the crystallite has a dramatic impact on the PL of this material.; Finally a study was performed on the sensitivity of the PL of porous silicon to oxygen. The study showed that at low temperatures the visible PL of porous silicon was completely quenched when exposed simultaneously to oxygen and laser light. The PL could be partially recovered by removing the oxygen from the surface. These results can be explained by physisorption of oxygen to the surface of the microcrystallites which combined with the laser modifies the surface potential of the crystallites. This indicates that the surface of the crystallites plays a significant part in the PL of porous silicon.