Influence of laser excitation on raman and photoluminescence spectra and FTIR study of porous silicon layers

Abstract

A porous silicon lm PS was investigated by FTIR, Raman and photoluminescence PL spectroscopies. The Raman and PL spectra were obtained using four di erent laser excitations: 488, 514, 633 and 782 nm. The analysis of the rst order and second order Raman scattering lines permits to identify the band energy structure of the crystallites inside the PS lm. The analysis of PL spectra shows that the intensity and full width at half-maximum values of PL emission depends on intensity and energy of laser excitation. The linear polarization degree LPD of the PL spectra also presents a dependence of laser excitation. The observed dependence of Raman and PL spectra due to laser excitation energy cannot be explained within the quantum con nement alone. We propose a mechanism for PL emission in PS layers, in which the radiative recombination occurs in localized centers at pore crystallite interface. These quasi-molecular centers are Jahn-Teller active. I IntroductionSince the original reports of e cient photoluminescence PL from porous silicon PS 1,2 the mechanism of the PL from PS is the subject of numerous investigations and discussions 3 . Although experimental evidence has been given for the quantum con nement model 4 , ample arguments and experimental facts have shown that, in silicon nanocrystals with surface passivated by o xide, the PL originates from some radiative centers at the nc , Si=SiO 2 interface 5 . One of the apparently unresolved problems is the large discrepancy between the calculated bad gap of the small silicon nanocrystals 6 and the observed distribution of PL spectra 7 . Here we discuss the surface structure, bonding and disorder in PS lms related to PL emission using Fourier Transform Infra Red FTIR , Raman and PL spectroscopies. II Experiments and ResultsPorous silicon PS was prepared by electrochemical anodization using a Si, p 100 oriented wafer with a re- The FTIR spectra of samples were obtained in the BIO-RAD system using transmission technique. The Raman and photoluminescence PL spectra were obtained on a Renishaw Raman system 3000 equipped with CCD detector and an Olympus BH-2 microscope. Measurements were made in the back scattering geometry using a 80 microscope objective to focus the laser beam on the sample. The area of the laser spot on the sample using the 80 objective is ca. 2 m 2 m In order to correlate surface structure of PS with PL emission, samples A and B were analyzed by FTIR spectroscopy see Fig. 1 . The PL spectra of this samples were obtained by excitation with The PL spectra of these samples were obtained by excitation with 488 nm laser source of 10 Watts.

Tunable characteristics of porous silicon optical microcavities by energetic N ion beam interactions

“…FTIR spectroscopy describes that Si-O-Si stretching vibrations modes are ascribed to silicon dioxide at the surface of these irradiated microcavities. The presence of different Si-O x -H y complexes points out that some silicon hydride and silicon oxide sites are present [51][52][53][54]. The results deduced from FTIR are summarized, which corroborates with the picture presented earlier.…”

l-Proline Functionalized Dicationic Framework of Bifunctional Mesoporous Organosilica for the Simultaneous Removal of Lead and Nitrate Ions

“…The peaks at the Raman shifts 633.4 and 967.7 cm −1 represent the stretching modes of Si− O−Si and Si−C bonds, respectively, while the peak at 1123.7 cm −1 belongs to the bending C−H bond (alkyl group). 44 After the adsorption treatment, a new peak appears at the Raman shift 1042.3 cm −1 that corresponds to the symmetric stretching mode of the adsorbed NO 3 − ions on the solid surface. 45 Ren and group have similarly analyzed amine-crosslinked reed (ACR) after nitrate loading and obtained a spectra of the Raman shift at 1043.9 cm −1 for the NO 3 − ions.…”

“…The Raman spectra of BPBMO obtained before and after the treatment of Pb­(NO 3 ) 2 solution are shown in Figure b. The peaks at the Raman shifts 633.4 and 967.7 cm –1 represent the stretching modes of Si–O–Si and Si–C bonds, respectively, while the peak at 1123.7 cm –1 belongs to the bending of C–H bond (alkyl group) . After the adsorption treatment, a new peak appears at the Raman shift 1042.3 cm –1 that corresponds to the symmetric stretching mode of the adsorbed NO 3 – ions on the solid surface .…”

Changes in the porous silicon structure induced by laser radiation

“…34 On the other hand, the Si-O-Si bending mode vibration at 480 cm 1 , observed by infrared spectroscopy, is intensified in PS sample oxidized in the presence of air. 35 In this sense, it seems that before and after laser heating there are different surface species giving rise to the broad feature near 480 cm 1 causing an accidental degeneracy. Finally, the Raman spectra present signals in the 1900-2400 cm 1 spectral region (see Fig.…”