Abstract:

This work concerns the structural and optical properties of Porous Silicon. Porous silicon was already known from 1956 when Uhlir at Bell Laboratories in USA discovered that for certain substrate type and resistivity, and for certain electrolyte concentration and current density, silicon could be dissolved anodically in hydrofluoric acid based electrolytes. Localized attack of the silicon substrates led to the formation of a porous silicon layer. In 1984 Pickering et al observed luminescence from this material but it was not until Canham observed efficient visible luminescence at DRA in the UK in 1989 that porous silicon received much attention worldwide as a material for potential optoelectronic applications. Various models have been put forward to explain the light emission in porous silicon. From all of these models the quantum confinement model which considers that the luminescence in porous silicon originates from quantum confinement of carriers in the fine structures of the porous silicon skeleton seems to cope well with the experimental data. Chronoamperometry and gravimetric measurements give information about the degree of the porosity in this material whereas TEM and SEM reveal the fine structure of the pores. Double crystal x-ray diffraction patterns obtained from porous silicon imply that the porous silicon layer is tetragonally distorted and lattice matched to the substrate, the strain increasing with increasing porosity. Electron beam diffraction patterns show that an amorphous phase may be present in the material, but the bulk of it remains crystalline. Infra-red absorption measurements indicate that silicon-hydrogen-oxygen complexes are present in the internal surface of porous silicon playing a significant role in light emission. ESR measurements show that hydrogen and oxygen in particular are important in the passivation of the surface dangling bonds. It is shown that increase in the porosity of this material or in other words decrease in the size of the fine structures constituting the porous silicon skeleton shifts the luminescence band to higher energies. This finding agrees well with the quantum confinement model. However post-treatments such as annealing in vacuum or oxidation cause vast changes in the internal surface of the material as well as in its photoluminescence properties. This observation indicates that changes in the chemical composition of the surface are important in the luminescence process. Unusally long luminescence decay times observed in porous silicon imply some similarities with disordered materials such as amorphous silicon. To date no answer on the important issue of the origin of the light emission in porous silicon exists.

Notes:

Copyright - Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.Last updated - 2023-03-08

Website