Optical and microstructural investigations of porous silicon (original) (raw)
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Raman scattering and photoluminescence study of porous silicon formed on n-type silicon
Bulletin of Materials Science, 1994
We report Raman scattering and photolumineseenee studies on porous silicon film formed on n-type silicon. The Raman spectra over the sample surface exhibit considerable variation whereas the photoluminescence spectra are practically identical. Our results indicate that, well inside the film surface, it consists of spherical nanocrystals of typical diameter ~ 100/~, while on the edge these nanocrystals are 1> 300 ,~. We further observe that there is no correlation between the photoluminescence peak position and the nanocrystal diameter. This suggests that the origin of the photoluminescence is due to radiative recombination between defect states in the bulk as well as on the surface of the nanocrystal.
Effect of Silicon Crystal Size on Photoluminescence Appearance in Porous Silicon
ISRN Nanotechnology, 2011
The photoluminescence (PL) study in porous silicon (PS) with decreasing Si crystallites size among the pores was reported. The PL appearance is attributed to electronic confinement in columnar-like (or dotlike) structures of porous silicon. Three different pore diameter PS samples were prepared by electrochemical etching in HF-based solutions. Changes in porous silicon and Si crystallite size were studied by observing an asymmetric broadening and shift of the optical silicon phonons in Raman scattering. Fourier transform infrared spectroscopy (FTIR) was used to study the role of siloxene or other molecular species, for example, SiH x in the luminescence mechanism. This mechanism was further studied by thermal annealing of PS at different temperatures. The PL of PS sample annealed at ≥300 • C for 1 hr shows that trap electronic states appear in the energy gap of the smaller nano-crystal when Si-O-Si bonds are formed. From the observation of PL, Raman, and FTIR spectroscopy, the origin of PL in terms of intrinsic and extrinsic properties of nanocrystalline silicon was discussed.
Applied Surface Science, 2003
Porous silicon layers (PSLs) were prepared in ethanoic and aqueous HF solutions using the conventional electrochemical etching technique. The microscopic structure of the PSLs has been studied by polarised photoluminescence (PL), Raman scattering and atomic force microscopy (AFM). We found that parallel (I // ) and perpendicular (I c ) polarised PL present quite different line shapes. By assuming PS as a mixture of quantum wires (QWs) and quantum dots (QDs) nanocrystallites having speci®c mean diameter sizes and proportions, we give an explanation to the polarised PL behaviour. This PS modelling enable us to obtain calculated Raman spectra that ®t very well the experimental ones for PSLs formed in ethanoic HF solution. AFM images of PSLs prepared in pure aqueous HF solution show morphological inhomogeneities as anodisation time increases, leading to non-conventional and reproducible PL and Raman behaviours. The latter PL behaviour was explained as being due to the non-uniformity of etching in aqueous HF, while that of the Raman spectra was described by introducing an amorphous phase beside the QWs and QDs contribution. #
Raman Spectroscopy of Porous Silicon
Handbook of Porous Silicon, 2018
Raman spectroscopy is being utilized to characterize porous silicon (PS) structures, not only for optoelectronic but also for sensing applications like SERS and biomedical uses. This review focuses on the large body of work extracting nanocrystallite size distibutions from Raman signals. Raman scattering of PS can give valuable information on properties of nanosized silicon structures that strongly depend on the symmetry, structural geometry, morphology, pore diameter, skeleton size, etc. The phonon confinement model of the first order optical phonons at 521 cm À1 is often used to analyze Raman scattering band shapes of porous silicon and hence to determine the size of crystallites embedded in the porous layer. Particles of nanometric size also show low-frequency acoustic vibrational modes that can be observed by Raman spectroscopy.
Study of porous silicon structure by Raman scattering
In this paper, the effect of etching time on light emitting porous silicon has been studied by using Raman scattering. Enhancement of Raman intensity by increasing the porosity is observed. Also there is a red shift, about 4 cm −1 , from the Raman peak of crystalline silicon to that of porous silicon. The phonon confinement model suggests the existence of spherical nanocrystalline silicon with diameter around 7 nm. But SEM images show that the samples have a sheetlike structure that confines phonons in one dimension. This should not cause any shift in their Raman spectra. It is suggested that the observed Raman peak shift is due to the spherical nanocrystals on the surface of these sheets.
Correlation of Raman and photoluminescence spectra of porous silicon
Applied Physics Letters, 1992
Porous GaAs was formed by electrochemical etching of n-type GaAs wafers in HF-or HCl-based solution with different current densities. The porous structure formation has been confirmed by scanning electron microscopy and x-ray diffraction. The samples were subjected to Raman and photoluminescence (PL) spectroscopic investigations. Our results show that the spontaneous emission is originated from extremely small structures. As the porosity increases, there is an increase of the luminescent peak, lower energy shifting of the Raman feature, exhibiting broadening and decreased of first-order longitudinal optic mode peak intensity. In addition, the intensity of the transverse optic (TO) mode was highly enhanced and its peak was broadened due to the breakdown of the polarization selection rule in the case of high-porosity samples. Two new peaks around 200 and 233 cm −1 were observed, which were attributed to α-As and TO-Ga-As-a respectively. Both Raman and PL results were explained using quantum confinement models. There is reasonable agreement between the results obtained from PL and Raman spectroscopic investigations of the etched GaAs samples.
Spectroscopic Investigation of Porous Silicon Prepared by Laser-Induced Etching
… of optoelectronics and …, 2008
Porous silicon was prepared by using an argon-ion laser in a laser-induced etching process with different etching time. Scanning electron microscopy was used to monitor changes in surface morphology produced during the etching process. Porous silicon samples were subjected to spectroscopic investigations. The first-order Raman line asymmetry was found to decrease with increase of the etching time, while the peak position downshifted for a given power density. The photoluminescence spectra (PL) exhibit a blue shift in peak position with etching time. Both Raman and PL data were explained using appropriate quantum confinement models involving three-dimensional confinement and Gaussian size distributions of nanocrystallites constituting porous silicon samples. There is reasonable agreement between the results obtained from Raman and PL spectroscopic investigations of the PS samples.
Correlation of photoluminescence spectra and structure of porous silicon
Semiconductor Science and Technology, 1996
Porous silicon (PS) layers emitting red photoluminescence (PL) have been prepared by anodization of p-type (100) monocrystalline silicon substrate in aqueous HF solutions. PS layers oxidized in free air exhibit under UV photoirradiation an intense yellow-orange PL, whilst as-prepared samples emit red PL. Our aim is to explain the PL behaviour and its origin in both unetched and HF etched as-prepared and oxidized PS layers according to calculated PL based on quantum confinement formalism and to infrared spectroscopy (IRS). It was found that the PL behaviour is associated with a quantum size effect and concentration change in quantum dots and wires. It was observed that HF etching of oxidized PS may induce a preponderance of dots or wires in the PS structure, depending on the oxidation degree, and produce a PL blueshift or redshift respectively. By correlating PL spectra of unetched and HF-etched oxidized PS, we found that highly oxidized PS transforms into an SiO 2 matrix in which photoluminescent nanocrystalline Si quantum dots are embedded.
Nanostructure and optical propertes of porous silicon layer
Maǧallaẗ ǧāmiʻaẗ kirkūk, 2015
In this paper nanostructures Porous silicon layers have been prepared by electrochemical etching (ECE) technique of (111) P-type silicon wafer with a solution Electrolytic HF: ethanol at a concentration of 1:2 with various anodization currents and etching time of 20 min. The morphological, structural and optical properties of nanostructure porous silicon were investigated by Atomic Force Microscopy (AFM), X-Ray Diffraction (XRD) and Photoluminescence (PL) respectively. From AFM images, we found that the PS layer has sponge like structure, and average diameter of pore and thickness of PS layer increased with increasing of the anodization currents. X-ray diffraction show that the crystal size was reduced toward nanometric scale, and then a broadening of diffraction peaks (111) was observed. The band gap of the samples was measured through the photoluminescence (PL) peak.
Raman scattering study of microstructure of n-type porous silicon
Solid State Communications, 1997
We report a detailed Raman scattering study of porous silicon film prepared on n-type silicon substrate. We observe large enhancement of Raman scattered signal and also that with increase in laser power the Raman line shape shows low frequency asymmetry, decrease in frequency of the peak position and reduction in signal enhancement. Our results could be explained consistently only by considering a two layered model of the microstructure of these films. We argue that this is a simple and nondestructive technique to look at the layered nature of the microstructure of these materials -so far seen only by high resolution electron microscopy.