No abstract

We have measured depth-resolved microphotoluminescence ͑PL͒ and micro-Raman spectra on the cross section of porous silicon multilayers to sample different layer depths. The PL emission band gets stronger, blueshifts, and narrows at the high porosity layers. On the contrary, the Raman band weakens and broadens. This band is fitted to the phonon confinement model. With the bulk silicon phonon frequency and its linewidth as free parameters, we obtain crystallite size, temperature, and stress as a function of depth. Sizes are larger than those estimated from PL. Laser power was reduced to eliminate heating effects. Compressive stresses in excess of 10 kbar are found in the deepest layer due to the lattice mismatch with the substrate.

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.

No abstract

No abstract