Depth-resolved microspectroscopy of porous silicon multilayers

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.

Spectral and Morphological Studies of Nanocrystalline Silicon Thin Films Synthesized by PECVD for Solar Cells

“…Since the interpretation of the Raman measurements largely influences the estimated structural data, RS has to be combined with other methods, typically microscopy or XRD. Manotas et al [34] combined microphotoluminescence and micro-Raman spectra taken on the cross-section of porous silicon multilayers to get direct depth-resolved information, but the spatial resolution of these methods cannot reach nanometric scale. RS spectroscopy results were combined with grazing incidence small angle X-ray scattering (GISAXS) results as well, but the crystals seen by RS and the ''particles'' seen by GISAXS are not necessarily the same objects [31].…”

In-depth RBS study of optical layers based on nanostructured silicon

“…Moreover, the presence of a high concentration of defects at the PS/Si interface suggests that PS formation and propagation occurs through these defects. In addition, Raman measurements [9] have also revealed the existence of a transition layer in the PS/silicon interface with a high density of dislocations and compressive stress forces as high as 13 kbar with lower porosity than expected. Hence, RBS results obtained in the present work further support these observations.…”

“…Accordingly, the accurate analysis of the composition and morphology of PS is of great importance to precisely control its behavior. Up to now, many studies about the structure of PS by the use of different techniques such as transmission electron microscopy (TEM) [3][4][5], X-ray diffraction (XRD) [6][7][8] and Raman spectroscopy [9], have been reported. In particular, we have previously investigated in detail the structure of PS by means of high-resolution transmission electron microscopy (HRTEM) and digital image processing [10,11].…”

HRTEM analysis of the nanostructure of porous silicon

“…In particular, the Si/PS interface will play an important role on the optoelectronic behavior of PS-based devices. Up to now, many studies about the structure of PS by the use of different techniques, such as transmission electron microscopy (TEM) [4][5][6][7], X-ray diffraction (XRD) [8][9][10][11][12] and Raman spectroscopy [13] among others, have been reported. However, the formation mechanisms of PS are still unclear due to the difficulty of characterizing very thin porous layers.…”