Anodisation-related structural variations of porous silicon nanostructures investigated by photoluminescence and Raman spectroscopy (original) (raw)

Optical and microstructural investigations of porous silicon

Bulletin of Materials Science, 2005

Raman scattering and photoluminescence (PL) measurements on (100) oriented n-type crystalline silicon (c-Si) and porous silicon (PS) samples were carried out. PS samples were prepared by anodic etching of c-Si under the illumination of light for different etching times of 30, 60 and 90 min. Raman scattering from the optical phonon in PS showed the redshift of the phonon frequency, broadening and increased asymmetry of the Raman mode on increasing the etching time. Using the phonon confinement model, the average diameter of Si nanocrystallites has been estimated as 2⋅ ⋅9, 2⋅ ⋅6 and 2⋅ ⋅3 nm for 30, 60 and 90 min samples, respectively. Similar size of Si crystallites has been confirmed from the high resolution transmission electron microscopy (HRTEM). Using 2TO phonon mode intensity, we conjectured that the disordered Si region around the pores present in 30 min PS dissolved on etching for 90 min. The photoluminescence (PL) from PS increased in intensity and blue shifted with etching time from 2⋅ ⋅1-2⋅ ⋅3 eV. Blue shifting of PL is consistent with quantum confinement of electron in Si nanocrystallites and their sizes are estimated as 2⋅ ⋅4, 2⋅ ⋅3 and 2⋅ ⋅1 nm for 30, 60 and 90 min PS, respectively which are smaller than the Raman estimated sizes due to temperature effect. Unambiguous dominance of quantum confinement effect is reported in these PS samples.

Characteristics of Nanostructure Porous Silicon Prepared by Anodization Technique

2013

Porous silicon (PS) layers are prepared by anodization for different current densities. The samples are then characterized the nanocrystalline porous silicon layer by X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), Fourier Transform Infrared (FTIR), Reflectivity and Raman. PS layers were formed on a p-type Si wafer. anodized electrically with a 10 and 40 mA/cm 2 current density for fixed 20 min etching times. We have estimated crystallites size from X-Ray diffraction about nanoscale for porous silicon and AFM confirms the nanometric size and therefore optical properties about nanocrystalline silicon yields a Raman spectrum showing a broadened peak shifted below 520 cm -1 .

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.

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.

Optical study and synthesis of porous silicon nanostructures

Indian Journal of Pure & Applied Physics, 2006

Porous silicon nanostructures have been generated using laser assisted etching (photochemical etching). The shape and size of the nanostructures obtained, depend on the wavelength used. The dependence of Raman shift and photoluminescence on the shape and size of nanostructures was studied.

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.

Direct evidence for the amorphous silicon phase in visible photoluminescent porous silicon

Applied Physics Letters, 1992

We report on micro-Raman spectroscopy studies of porous silicon which show an 'amorphous silicon Raman line at 480 R cm-' from regions that emit visible photoluminescence. A Raman line corresponding to microcrystalline silicon at 510 R cm-' is also observed. X-ray photoelectron spectroscopy data is presented which shows a high silicon-dioxide content in porous silicon consistent with an amorphous silicon phase. Recent reports' on the visible photoluminescence (PL) of porous silicon (PS) at room temperature have triggered much discussion on possible mechanisms for this phenomenon" and created the possibility of optoelectronic applications.' The observed phenomenon cannot be explained in terms of bulk silicon properties since the indirect band gap of silicon is in the near infrared. One recently proposed explanation is based on the assumption that highporosity silicon can be considered to be a network of nanometer-size crystalline wires, and that quantum confinement effects in these one-dimensional structures are responsible for the widening of the band gap.' Earlier reports that the observed effect could be caused by hydrogen and/ or oxygen atoms incorporated in an amorphous silicon (a-Si) matrix4 were not considered due to the lack of direct evidence for the existence of the a-Si phase.' In this letter, we present, for the first time, direct evidence for the a-Si phase in PS based on micro-Raman spectroscopy. The PS samples were made from p-type, boron-doped, (100) crystalline silicon (c-Si) wafers with a resistivity of 10-20 n cm, similar in resistivity to the p substrates used in Ref. 1. Silver was painted on the back of the wafers to produce a uniform potential and etching current on the front surface. The front surface was placed in a 40%-50% HF acid solution and electrochemically etched using constant current densities in the range 10-50 mA/cm2. Typical etching times were 10-15 min. The etched surface was studied using scanning electron microscopy and scanning tunneling microscopy and was found to have a morphology consisting of a random array of small circular pores. This type of morphology is typically observed when using lightly doped p substrates.5 The PS samples emitted bright red to yellow PL visible to the naked eye when excited by the 514.5-nm line of an argon laser or ultraviolet light. Room-temperature Raman and PL measurements were performed using a micro-Raman system in which the laser spot size could be focused to 1 pm in diameter and positioned on the sample under an optical microscope. The

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.

Photoluminescence and Raman study of iron-passivated porous silicon

Materials Science and Engineering: B, 2003

Degradation of porous silicon (PS) fabricated by laser-induced etching was studied using photoluminescence (PL) and Raman spectroscopy. Freshly prepared samples were given a heat treatment in hydrofluoric acid plus ferric nitrate solution to produce ironpassivated porous silicon (IPS) samples. PL measurements on IPS show different peak positions and widths as compared to freshly prepared non-passivated PS samples. Results were analyzed using a quantum confinement model. Exposing IPS to air for more than 4 months resulted in no degradation of PL intensity or changes in the peak position and size distribution. Raman spectra of IPS also revealed changes in line-shape asymmetry in comparison to freshly prepared non-passivated PS samples. The data were explained using the phonon confinement in two-dimensions. There is good agreement between PL and Raman data for the size of nanocrystallites participating in iron-passivation.

Correlation of optical and structural properties of light emitting porous silicon

Applied Physics Letters, 1993

Microscopic structures of light emitting porous silicon layers have been studied. The samples prepared in an aqueous HF solution by anodizing p-type silicon substrates show a strong positional dependence of photoluminescence and Raman spectra. The photoluminescence peaks are broad around 1.8 eV, where the photoluminescence intensities are comparable to that of GaAs at 5 K. We have found from Raman studies showing two characteristic peaks at 500 and 520 cm−1 that microscopic structures reveal gradual changes from porous silicon to a mixture of polycrystalline and hydrogenated amorphous phases as the probing spot is moved to the edge of the sample. This is explained by the redeposition of silicon atoms on top of the porous silicon layers near the edge of the sample as a result of liquid flow caused by bubbles of hydrogen gas which was produced near the surface of the sample during the anodization process.