Study Of Porous Silicon Modified By Surfactants And Temperature Dependence Of Spectroscopy For Porous Silicon

It is reported firstly by CanHam in 1990 that porous silicon can exhibit visible photoluminescence at room temperature. Since then it has generated much interest all over the world, because achieving visible-light emission from crystalline Si has remained a formidable task due to the fundamental band-structure limitation: a small and indirect band gap at room temperature. The observation of visible-light emission from porous silicon has begun to revitalize silion's role as a material for optical electronics.The history, background, preparation and form of PS is introduced in the first chapter. Then the origin of this visible-light emission is disscused. Each model has its advantage in some specific cases, but meets difficulties in other cases. We suggest both the quantum confinement effect and the surface state mechanism should be considered in order to understanding photoluminescence of PS. Afterward the application of PS is anticipated. In the second chapter, porous silicon is surface modified with four kinds of surfactants: Sodium dodecyl sulfate, Cetyl pyridinium bromide, Sodium oleate and OP. It is found that Sodium dodecyl sulfate enhance PL intensity, but others weaken it. Sodium dodecyl sulfate solution with different concentration enhance differently. The work offers a new and effective way to improve the PL characteristic of PS.In the third chapter, the temperature dependence of PL of porous silicon is investigated. At lower temperature, the PL intensity enhance firstly as decreasing temperature, then weaken. One sample named A1 shows two-peak PL (H peak and L peak) at room temperature. The wavelength and intensity of H peak remain still asincreasing temperature above room temperature, but the wavelength blue-shifts and intensity increases gradually for L peak in the same process. The PL peak of the sample named A2 shifts to lower energy and intensity decreases as increasing temperature above room temperature. The quantum confinement effect or the surface state mechanism can not explain the phenomena in singles. The quantum confinement effect is a key factor of photoluminescence of PS, and the surface state mechanism plays an important role in the conditions. The fourth chapter is the Raman study of porous silicon. Only a sharp single band near 520 cm-1 appears in the Raman spectrum of porous silicon when the exciting laser power is low. The Raman peak shifts to the red side with the increase of the laser power and shows dissymmetrical extension. The phenomena are discussed elementarily. The Raman band is splinted into two bands when laser power gets strong enough. The Raman band shifts to the red side and shows dissymmetrical extension can be explained as quantum confinement effect. We attributed the appearance of the double bands to the non-degeneracy of the LO and TO phonons...