Optical Properties Of Silicon Nanowires Research Articles

Systematic study of the structural, electronic and optical properties of silicon nanowires

In this work we analyzed the structural, electronic, and optical properties of a set of silicon nanowires oriented in different directions, using the density functional theory. Structural optimization was performed in order to relax the atomic coordinates and cell parameters, after which the electronic band structure and density of states were obtained. Simultaneously, we computed the imaginary part of the dielectric function using the elements of the dipolar matrix. Furthermore, we related the transitions between the Van Hove singularities in the density of states with peaks in the absorption spectra, thus identifying relationships among them, which could be used to characterize the density of states by means of the absorption spectrum. The results showed that the electronic and optical properties depend on the diameter and orientation of the nanowires.

Next-generation Cost- Effective Photovoltaic Cell with Tailored Structural and Optical Properties of Silicon nanowires with Silver Nanoparticle Deposition

Next-generation Cost- Effective Photovoltaic Cell with Tailored Structural and Optical Properties of Silicon nanowires with Silver Nanoparticle Deposition

Optical Properties of Silicon Nanowires Obtained by Metal-Assisted Chemical Etching Using Gold Nanoparticles

Optical Properties of Silicon Nanowires Obtained by Metal-Assisted Chemical Etching Using Gold Nanoparticles

Highly improved optical properties of silicon nanowires by deposition of Poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] polymer

This paper reports on the effect of the Poly[2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) deposition on the chemical composition and the optical properties of silicon nanowires (SiNWs). The SiNWs were obtained by a single-step Ag-assisted chemical etching method, and then coated by MEH-PPV polymer using the electroless dipping method. Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Fourier Transformed Infra-Red (FTIR) spectroscopy were used to probe the deposition of the polymer on the SiNWs surface and its chemical interaction with them. The optical properties of the elaborated samples were investigated by photoluminescence (PL) spectroscopy. The PL spectra show that the PL emission range of the nanowires is practically the same as that of the MEH-PPV. We also get an enhancement of five orders of the integrated PL intensity of MEH-PPV/SiNWs sample compared to that of untreated SiNWs sample. The PL intensity enhancement is attributed to the luminescent centers of MEH-PPV molecules as well as the passivation of silicon nanowires surface. Interchain and intrachain transitions in the polymeric layer as well as the carriers transfer between SiNWs and MEH-PPV are the main sources of the multiband PL spectra.

Influence of nanostructure geometry on light trapping in solar cells

The aim of this research was to detect the influence of the silicon nanowires geometry and silver nanoparticles on the wafer surface on light trapping for application in solar cells with radial p–n junction. Si-NWs arrays were fabricated on p-type (100) silicon wafers with specific resistance of 10 Ω × cm. We used MacEtch method to form Si nanowires. In our study to deposit the additional silver nanoparticles on the surface of the nanowires, the flushing time was reduced to 10 min. The structural and optical properties of silicon nanowires were studied. The absorption, transmittance and reflectance spectra for periodic nanostructures with different parameters were calculated by FDTD (Finite-Difference Time-Domain) method. The FDTD method is a powerful numerical algorithm for direct solution of Maxwell’s equations. The realization of this method is discrete both in space and in time. The presented structures are described on a discrete mesh consisting of Yee cells and the Maxwell equations. They are solved discretely over time on this grid. As a result, through the method of the catalytic etching, we obtained nanowires of 0.5–2 μm in length and diameter in range of 50–100 nm. The diameter of silver nanoparticles was in the range of 20–50 nm. The reflection coefficient of light in wide spectral range was less than 1%. Reflection spectra peaked at the wavelength of 850 nm that points out on the influence of Ag nanoparticles.

Thermally induced evolution of the structure and optical properties of silicon nanowires

In the present paper, we report on the investigation of thermal annealing (TA) effect on structural and optical properties of crystalline silicon nanowires produced by metal-assisted chemical etching approach. In particular, the impact of TA on nanowire length, relative volume and size distribution of voids is described in terms of Lifshitz-Slyozov-Wagner theory considering the TA induced Oswald ripening in the SiNW arrays. It was also found that TA leads to a decrease of the SiNWs total reflection in the wide UV–VIS-IR spectral range. The reported effects can be used for tuning of crystalline SiNWs arrays in view of their further applications in photonics related fields.

Investigation of effective near-infrared light-trapping structure with submicron diameter for crystalline silicon thin film solar cells

To obtain high efficiency in crystalline silicon thin-film solar cells, it is necessary to develop a novel light-trapping structure that not only has high light absorptance and can be fabricated with a small etching margin but also has a small surface area for a small effect of surface recombination. In this study, optical properties of silicon nanowires (SiNWs) with submicron diameters were investigated by the finite-difference time-domain (FDTD) method in the infrared wavelength region, in which the absorption coefficient of crystalline Si is quite low and the increase in optical path length is very important. To verify the simulation results, SiNWs with submicron diameters were successfully fabricated by the metal-assisted chemical etching method using two types of etching masks. The optical properties and minority carrier lifetime of the obtained structures were measured, and the results suggest that SiNWs with submicron diameters such as ∼700 nm are effective for both light trapping and the suppression of surface recombination.

Optical Properties of Silicon Nanowires Fabricated by Environment-Friendly Chemistry.

Silicon nanowires (SiNWs) were fabricated by metal-assisted chemical etching (MACE) where hydrofluoric acid (HF), which is typically used in this method, was changed into ammonium fluoride (NH4F). The structure and optical properties of the obtained SiNWs were investigated in details. The length of the SiNW arrays is about 2 μm for 5 min of etching, and the mean diameter of the SiNWs is between 50 and 200 nm. The formed SiNWs demonstrate a strong decrease of the total reflectance near 5–15 % in the spectral region λ < 1 μm in comparison to crystalline silicon (c-Si) substrate. The interband photoluminescence (PL) and Raman scattering intensities increase strongly for SiNWs in comparison with the corresponding values of the c-Si substrate. These effects can be interpreted as an increase of the excitation intensity of SiNWs due to the strong light scattering and the partial light localization in an inhomogeneous optical medium. Along with the interband PL was also detected the PL of SiNWs in the spectral region of 500–1100 nm with a maximum at 750 nm, which can be explained by the radiative recombination of excitons in small Si nanocrystals at nanowire sidewalls in terms of a quantum confinement model. So SiNWs, which are fabricated by environment-friendly chemistry, have a great potential for use in photovoltaic and photonics applications.

Effects of silver and gold catalytic activities on the structural and optical properties of silicon nanowires

The metal-assisted chemical etching of silicon in an aqueous solution of hydrofluoric acid and hydrogen peroxide is established for the fabrication of large area, uniform silicon nanowire (SiNW) arrays. In this study, silver (Ag) and gold (Au) are considered as catalysts and the effect of different catalysts with various thicknesses on the structural and optical properties of the fabricated SiNWs is investigated. The morphology of deposited catalysts on the silicon wafer is characterized by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). It is shown that the morphology of the fabricated silicon nanostructures remarkably depends upon the catalyst layer thickness, and the catalyst etching time directly affects the structural and optical properties of the synthesized SiNWs. FESEM images show a linear increment of the nanowire length versus time, whereas the etching rate for the Au-etched SiNWs was lower than the Ag-etched ones. Strong light scattering in SiNWs caused the total reflection to decrease in the range of visible light, and this decrement was higher for the Ag-etched SiNW sample, with a longer length than the Au-etched one. A broadband visible photoluminescence (PL) with different peak positions is observed for the Au- and Ag-etched samples. The synthesized optically active SiNWs can be considered as a promising candidate for a new generation of nano-scale opto-electronic devices.

Structural and optical properties of silicon nanowires synthesized by Ag-assisted chemical etching

Metal-assisted chemical etching (MACE) of silicon in an aqueous solution of hydrofluoric acid and hydrogen peroxide is established for the fabrication of large-area uniform silicon nanowire (SiNW) arrays. The effect of the silver catalyst layer thickness on the morphology of the synthesized nanostructures and nanowires is investigated. Atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) reveal that the morphology of the fabricated silicon nanostructures remarkably depends on the catalyst layer thickness, and an optimum layer thickness is necessary for the fabrication of SiNWs. Also the effect of different etching times on the structural and optical properties of the fabricated SiNWs is investigated. FESEM showed a linear increment of the nanowire length and slight diameter changes through different etching times. The ultralow reflectance of SiNWs in the absorption region through the measurement of specular and diffuse reflectance showed that with increase in the etching time, the total reflectance remarkably decreases. A broadband visible photoluminescence (PL) emission from these wires was observed, and it could be stated that the silicon nanocrystals (SiNCs) are mostly responsible for the PL emission. The SiNC sizes were determined by an analytical model through a frequency shift in the Raman spectrum. The synthesized optically-active SiNWs could, therefore, be considered as a promising candidate for a new generation of nanoscale opto-electronic devices.

Correlation between photoluminescence and structure in silicon nanowires fabricated by metal‐assisted etching

Structural and optical properties of silicon nanowires synthesized by metal‐assisted chemical etching are investigated. Macroscopic properties of nanowire arrays as well as microscopic photoluminescence (PL) and Raman scattering spectra of single nanowires are studied. The morphology of silicon nanowires changes depending on etching duration and concentration of H2O2 in the etching solution. In thick nanowires having small length and large diameter, red PL appears. Typical length and diameter are 90 μm and 600 nm, respectively. The PL spectrum is composed of two bands with the peaks at 635 and 705 nm. In thin nanowires having large length and small diameter with their ratio larger than 210, no PL appears. Clear correlation between the morphology of nanowires and the PL appearance is demonstrated. Transmission electron microscopy reveals the presence of porous structures of silicon at the top of nanowires. In the middle part of nanowires, the interface between silicon crystalline core and surrounding silicon oxide is smooth and no nanocrystal is present. Optical Raman microscopy for a single nanowire with the space resolution of ∼1 μm clarifies positions where the red PL appears. At the top of nanowires where porous structures of silicon are present, the red PL appears. At these positions, the Raman peak of the optical phonon mode of crystalline silicon becomes broad and shifted. These Raman spectra reflect silicon nanocrystals present at the top of the nanowire. The origin of the red PL in silicon nanowires is considered to be silicon nanocrystals present at the top of nanowires.

Effective index approximation for ordered silicon nanowire arrays

A semi-analytical model for the optical properties of silicon nanowires (SiNWs) is presented. Results from the model offer a good physical understanding of the optical behavior of SiNWs. It is shown that light trapping within ordered nanowires only happens over a small wavelength band (20–75 nm) that is dependent on the diameter of the nanowires, not length. Furthermore, wavelength tunable absorption peaks can be achieved in ordered SiNWs by adjusting the geometrical parameters. A good match between the model and experimental results confirms the validity of the proposed effective index model.

Growth of silicon nanowires-based heterostructures and their plasmonic modeling

ABSTRACTComplex nanoscale architectures based on gold nanoparticles (AuNPs) can result in spatially-resolved plasmonics. Herein, we demonstrate the growth of silicon nanowires (SiNWs), heterostructures of SiNWs decorated with AuNPs, and SiNWs decorated with graphene shells encapsulated gold nanoparticles (GNPs). The fabrication approach combined CVD growth of nanowires and graphene with direct nucleation of AuNPs. The plasmonic or optical properties of SiNWs and their complex heterostructures were simulated using discrete dipole approximation method. Extinction efficiency spectra peak for SiNW significantly red-shifted (from 512 nm to 597 nm or 674 nm) after decoration with AuNPs, irrespective of the incident wave vector. Finally, SiNW decorated with GNPs resulted in incident wave vector-dependent extinction efficiency peak. For this case, wave vector aligned with the nanowire axial direction showed a broad peak at ∼535 nm. However, significant scattering and no peak was observed when aligned in radial direction of the SiNWs. Such spatially-resolved and tunable plasmonic or optical properties of nanoscale heterostructures hold strong potential for optical sensor and devices.

Growth, Structure and Optical Properties of Silicon Nanowires Formed by Metal-Assisted Chemical Etching

Silicon nanowires (SiNWs) formed by metal(silver)-assisted chemical etching of lowly boron-doped (100)-oriented single crystalline silicon substrates in hydrofluoric acid solutions are investigated by means of the electron microscopy and optical spectroscopy (absorption and reflection measurements, photoluminescence spectroscopy and imaging). The growth rate of SiNWs is found to depend nonlinearly on the time of etching. The formed SiNW arrays demonstrate a strong decrease of the total reflectance below 1% in the full visible and near infrared region between 300 and 1000 nm and the samples show the similar optical properties as “Black Silicon,” which can be used as antireflection coating in photovoltaic applications. The prepared SiNWs exhibit efficient photoluminescence in the spectral region of 600–1000 nm and it is explained by the radiative recombination of excitons confined within nanostructured sidewall of SiNWs. The excitons luminescence is also observed in aqueous suspensions of SiNWs, whose application in bio-imaging is demonstrated in vitro.

Tailoring Optical Properties of Silicon Nanowires by Au Nanostructure Decorations: Enhanced Raman Scattering and Photodetection

Metallic nanoparticles (NPs) decorated semiconductor nanowires (NWs) heterostructures show significant promise in enhanced optical and opto-electrical properties due to the coupling of surface plasmon to nanowires. Here, we demonstrate a galvanic displacement based strategy to achieve in situ nucleation of Au nanoparticles and then postgrowth into higher order Au nanostmctures such as dimers, nanorods, and nanoprisms along the same Si nanowires (SiNWs). The presence of Au nanostructures significantly enhances the optical properties of nanowires. Particularly, a 24 times enhancement of Si Raman scattering signal was achieved with a Au dimer decoration. A Au nanorod aligned in parallel along nanowire strongly enhances the anisotropy of Si Raman scattering, with more than 28 times stronger signal under parallel polarization than that under perpendicular polarization, demonstrating for the first time the surface plasmon enhanced antenna effect. In addition, we demonstrate that surface plasmon enhances photocurrent of SiNW by almost 100%, which is higher than previous reports. Our studies show that SiNWs decorated with metallic nanostructures by in situ galvanic displacement exhibit significant promise toward high efficiency photodetection and light harvesting applications.

The structure and optical properties of silicon nanowires prepared by inductively coupled plasma chemical vapor deposition

Silicon nanowires were prepared by vapor–liquid–solid (VLS) mechanism at a growth temperature as low as 380 °C in an inductively coupled plasma chemical vapor deposition system. The nanowires consist of crystalline core surrounded by a thick amorphous silicon shell. An increase in plasma power produces dense and long nanowires with thick amorphous shell, accompanied with a thick uncatalyzed amorphous silicon film on the silicon substrate. Small catalyst nanoparticles are easier activated by plasma to grow the dense and thin nanowires in comparison with the large-size nanoparticles. Moreover, an enhanced optical absorption is achieved due to the strong light trapping and anti-reflection effects in the thin and tapered silicon nanowires with high density.

Optical Properties of Silicon Nanowires Fabricated by Electroless Silver Deposition

Vertically aligned silicon nanowires are fabricated on silicon substrates by electroless silver deposition, and their optical properties are investigated. The diameter of the nanowires ranges from 100 to 500 nm and their length ranges from 30 to 100 µm. Red photoluminescence appears at approximately 700 nm at room temperature. Its peak and intensity vary along the wire positions in Raman microscopy measurements. The photoluminescence intensity is high at the top of the wire. In this region, oxidation is enhanced and the Raman scattering spectra of the optical phonon mode tend to be broadened. The origin of the red photoluminescence is assumed to be defect states located at the interface between the core of the silicon nanowires and the surrounding silicon oxide.

Many‐body effects on the electronic and optical properties of Si nanowires from ab initio approaches

AbstractThe study of semiconducting nanowires is one of the most rapidly growing research areas in materials science and nanotechnology, not only from the point of view of the possible applications, but also regarding the use of the latest developments in the theory. In this paper, we review the general ab initio many‐body theory and methods and resume some of our very recent results regarding the structural, electronic, and optical properties of Silicon nanowires (Si‐NWs), outlining both the reached achievements and some of the technical aspects necessary to obtain them.

Influence of crystalline damage on morphological and optical properties of silicon nanowires

We have studied the effect of crystalline damage on the morphological and optical properties of silicon nanowires (SiNWs) formed by electroless etching. Ag nanoparticles were deposited on p-type Si wafers by electroless metal deposition (EMD). Then, the wafers were etched in HF/H 2O 2 solution for 15 min at 50 °C. The damage was previously introduced in silicon wafers by phosphorus implantation. Different damage levels were obtained by varying the dose and the energy of phosphorus ions implantation. The morphological and optical properties were studied using scanning electron microscope (SEM), spectroscopy of photoluminescence and reflectance.

Optical properties of silicon nanowires from cathodoluminescence imaging and time-resolved photoluminescence spectroscopy

Optical properties of silicon nanowires from cathodoluminescence imaging and time-resolved photoluminescence spectroscopy