Polarization effects on the Raman and photoluminescence spectra of porous silicon layers

Abstract

The e †ect of di †erent polarization orientations of the excitation source on the Raman and photoluminescence (PL) spectra of a porous silicon (PS) layer within two di †erent micro-regions was investigated. Two micro-regions (2 lm) along the (100) direction were studied, close to the crystalline silicon (c-Si)-PS layer interface and the PS layer-air interface. The Raman depolarization factors obtained in the 100-1200 cm-1 phonon spectra of these two micro-regions showed that the anisotropy presented by the PS layer is similar to that presented by the c-Si (100). Large di †erences in the Raman linewidths and di †erent emission maxima in the PL spectra were observed for the two micro-regions. These results were interpreted as the PS layer being inhomogeneous along the (100) direction. These e †ects are discussed from a critical point of view by taking into account quantum conÐnement and chemical composition of the nano-crystallite surface, since the stretching mode was also observed in the Raman SiH 2 spectra. Excitation with di †erent polarizations causes a shift of the emission maxima. This shift was assigned to a polarization dichroism caused by a breakdown on the degeneracy as the nano-crystallites having a reduced symmetry in relation to c-Si. The results strongly support the hypothesis that the luminescence presented by the PS layer is due to the presence of Si-based compounds on the surface of Si nanocrystallites.

Changes in the porous silicon structure induced by laser radiation

“…Therefore, it should be polarized if we consider conservation of local symmetry. However, in previous work, Salcedo et al 31 showed that this feature is depolarized. Based on these facts, we believe that this Raman signal is related to surface species containing Si-O-SiR or Si-Si-R moieties, where R can be H n , OH or another radical.…”

Nano-composite of porous silicon and organic dye molecules for optical gas sensor and lasing medium

“…This result showed a possible energy transfer process from the Ox-PS emission to Q absorption band on the ZnPc molecules, this is possible because the PL band emission of Ox-PS was extended within to spectral region of the absorption band on the ZnPc molecules (see Figure 2 (b)). The experimental measure of polarization coefficient (as defined in [5]) of PL emission at peak position (sample E, not presented in this paper) showed low value (0.12) as the same as of the emission spectra from the ZnPc in ethanol solution. The low polarization coefficient of ZnPc in ethanol is due to free rotation degree of dye molecules; in the case of the Ox-PS/ZnPc sample, the low polarization coefficient can be due to randomly oriented adsorption of the ZnPc molecules on Ox-PS surface.…”

“…The nano-composites Ox-PS/Dye structure showed highly stable PL emission even long time storage of samples in air ambient. (5) The PL behaviour of Ox-PS/dye film when submitted to different gas ambient suggest the possible application of these film in the optical gas sensor fabrication. (6) The similar PL features of Ox-PS/Rh-6G and Rh-6G (in organic solution) emission suggest that Ox-PS/Rh-6G film can be used as lasing medium in optical amplifier devices…”

“…2 Experimental Porous silicon (PS) layers were prepared by the electrochemical anodization method as describes elsewhere [5]. The obtained PS layer had 10 µm of thickness, 60 to 70 % of porosity with 2 to 3 nm of pores size.…”

“…PL emission spectra were obtained at backscattering setup with Renishaw Raman spectrometer. A detailed description of the optical setup for polarization measurement of PL spectra are described elsewhere [5]. The PL spectra were recorded using the laser lines at 488.0 nm (from an Ar + laser) and 632.8 nm (from a HeNe laser).…”