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A comparison of the compositional and photoluminescent properties of stain etched (SE) and anodically etched (AE) porous silicon (PS) samples has been carried out. The silicon substrates used and the laboratory conditions are the same for both types of etching processes. The study is carried out varying the PS surface properties by means of different cleaning procedures and post-etching ambient conditions. The results demonstrate that the evolution of the photoluminescence and the composition are related for both types of PS (AE and SE). Thus, it seems highly likely that the photoluminescence mechanisms involved in both cases are similar.

We have studied the stress in porous silicon films as a function of depth and porosity using micro-Raman spectroscopy. Raman spectra were measured at different points along a cross section cleaved normal to the layer planes. Each spectrum was fitted using the phonon confinement model with the bulk phonon wavenumber as a free parameter. From the variation of this parameter we get the stress using the known dependence of phonon frequency on stress for bulk silicon. We observe a compressive stress at the interface with the substrate due to the lattice mismatch between porous and bulk silicon. The maximum value of the stress increases with porosity. The results obtained by Raman micro-spectroscopy agree well with the lattice mismatch measured by X-ray diffraction reported in the literature.

This paper is focused to the study of the stabilization of the photoluminescent properties of porous silicon (PS). For this purpose, as-formed PS samples were subjected to different surface treatments. Photoluminescent excitation spectra were used to obtain the indirect band gaps, yielding practically the same values for PS films having undergone different surface annealing and post-etch treatments. However, the excitation spectra show a significant blueshift with aging for the different samples, which has been related to the initial amount of oxygen present in the porous surface as detected by XPS and FTIR. The variation of the intensity of the excitation spectra with aging has also been studied and can be associated to carbon contamination. The results are interpreted in terms of quantum size effects in PS and the influence of the surface composition.

This paper focuses on the study of the effect of anodic oxidation in porous silicon bilayers composed of two porous layers of different porosities. The order of the two types of layers has been alternated, and the thicknesses and refractive indices have been optically characterized by Fourier transform infrared spectroscopy. The results show that the refractive index of anodic oxidized porous silicon is reduced significantly with respect to just formed porous silicon. It is also observed that the quality of the oxidation is related to the porosity of the inner porous layer of the silicon bilayer structure. This effect is interpreted in terms of quantum size effects.

In this work we present a comparative study of porous silicon (PS) photoluminescence for samples stain etched and electrochemically etched. The etching parameters for both types of samples have been adjusted to obtain similar porous structures. The photoluminescence spectra have been obtained varying the excitation energy between 2.48 and 3.54 eV. The variation of the excitation energy produces differences in the evolution of the emission energy maximum between both types of PS. This behaviour is attributable to the differences in oxidation level in the porous structure. Also it has been established a higher concentration of luminescent centers for stain etched PS.

In this work we present the first experimental study of photocarrier lifetimes in p-type and n-type Si substrates in which stain etched porous silicon (PS) has been formed on the surface. The lifetime values have been obtained before and after the surface passivation of the samples. The surface pasivation has been produced by two different techniques: (i) hydrogen passivation by immersion of the samples in a HF solution; and (ii) deposition of SiNx in a plasma enhanced chemical vapour deposition system. The results show a degradation of the photocarrier lifetime when the porous layers are not adequately passivated. This lifetime degradation is mainly associated to a large concentration of rapid recombination centres located at the Si/PS interface. We have also detected a weak influence of the PS outermost dangling bonds to the photocarrier lifetimes.