Optical Properties Of Silicon Research Articles

Wavelength dependence of laser-induced excitation dynamics in silicon

Effect of laser wavelength on the carrier-phonon dynamics and damage threshold of silicon is studied numerically. Laser excitation dynamics in silicon is studied using Three-Temperature Model (3TM). We consider the evolution of electron, hole, and lattice temperatures separately and including band-gap re-normalization effect on optical properties of silicon. Finite Difference Time Domain method is used to model the laser field. Damage threshold calculated using the 3TM is in reasonable agreement with the experiments. Our results indicate that the competition of inter-band excitation, plasma heating, and electron–phonon relaxation process defines the damage threshold for various wavelengths and pulse durations.

Indirect light absorption model for highly strained silicon infrared sensors

The optical properties of silicon can be greatly tuned by applying strain and opening new perspectives, particularly in applications where infrared is key. In this work, we use a recent model for the indirect light absorption of silicon and include the effects of tensile and compressive uniaxial strains. The model is based on material properties such as the bandgap, the conduction and valence band density-of-states effective masses, and the phonon frequencies, which are obtained from first principles including strain up to ±2% along the [110] and [111] directions. We show that the limit of absorption can increase from 1.14 (1.09) to 1.35 μm (0.92 eV) under 2% strain and that the absorption increases by a factor of 55 for the zero-strain cutoff wavelength of 1.14 μm when a 2% compressive strain is applied in the [110] direction. We demonstrate that this effect is mainly due to the impact of strain on the electronic bandgaps of silicon, directly followed by the valence band density-of-states effective mass.

Changes in the geometric structure and hydrogen-termination modify the electronic and optical properties of porous silicon

Here, we show that the electronic and optical properties of silicon (Si) can be controlled by varying the amount of dangling bonds and the number of SiSi bonds in the system. By introducing pores in the bulk (in the form of Si vacancies), we can induce the appearance of gap states (states in the energy gap/forbidden region) in porous Si (pSi), as compared to pure Si. Terminating the Si atoms in the pores with hydrogen atoms (H) induces the disappearance of these induced gap states (IGS). As a result, we can continuously decrease (increase) the corresponding refractive indices of both pSi and H-terminated pSi by increasing (decreasing) the porosity.

Optical properties of silicon and germanium determined by high-precision analysis of reflection electron energy loss spectroscopy spectra

We present a detailed analysis and comparison of four models describing the extension of the electron-energy loss function from the optical limit of q\ensuremath{\rightarrow}0 into the (q,\ensuremath{\omega}) plane to obtain the bulk and surface terms of differential inverse inelastic mean free paths. We found that the best model that describes accurately and times efficiently the calculation of the energy loss function of free-electron-like materials is the combination of the Penn algorithm [Phys. Rev. B 35, 482 (1987)] with the Ritchie-Howie method [Philos. Mag. 36, 463 (1977)]. Applying this model in our reverse Monte Carlo method, we determined, with high-precision, electron-energy loss functions of silicon and germanium based on the theoretical analysis of the high-energy resolution reflected electron energy loss spectroscopy (REELS) spectra, measured at 3, 4, and 5 keV incident electron energies. The refractive index $n$, the extinction coefficient $k$, and the complex dielectric function ($\ensuremath{\varepsilon}={\ensuremath{\varepsilon}}_{1}+i{\ensuremath{\varepsilon}}_{2}$) were calculated from the obtained energy loss function in a wide energy loss range of 0--200 eV. The accuracy of the obtained results is justified with various sum rules. We found that the calculated optical data of Si and Ge fulfill the sum rules with an average accuracy of 0.11% or even better. Therefore, the use of these optical data in materials science and surface analysis is highly recommended for further applications.

Hydrofluoric acid pretreatment effect on the formation of silicon submicrometer particles by pulsed laser melting in liquid and their optical scattering property

Recently, the optical properties of silicon (Si) submicrometer spherical particles have been investigated to understand the dielectric nano-photonic function. Herein, we fabricated Si submicrometer spherical particles with high scattering efficiency using pulsed laser melting in deionized water or ethanol by irradiating laser at 66 mJ pulse−1 cm−2 via third harmonic of Nd:YAG laser. Hydrofluoric acid pretreatment was effective to remove surface oxide of raw Si particles; the laser fluence to obtain well crystallized spherical particles was lowered to 20 mJ pulse−1 cm−2 and the crystallinity of particles obtained were greatly improved without forming unwanted byproducts. The amount of particles was much more than those obtained by conventional fabrication technique. The particle size can be controlled by changing the laser fluence, and the scattering wavelength of colloidal solution can be controlled from visible to the near infrared range by increasing the laser fluence.

Spectrometer Can Fit Inside a Drone or Plane

Infrared device uses the optical properties of silicon

Effect of low-energy proton irradiation on parameters of silicon structures with n-p junction

The dependences of the separation probability of the Frenkel pair on the temperature and the position of the Fermi level in the band gap cause the dependences of primary radiation defects concentration on the irradiation temperature and impurity concentration. This conclusion is confirmed by study results of electrophysical and optical properties of silicon n+-p-p+ structures, irradiated by the proton flux with the energy of 40 keV and the fluence of 1015 cm−2.

Solution Synthesis, Surface Passivation, Optical Properties, Biomedical Applications, and Cytotoxicity of Silicon and Germanium Nanocrystals.

Silicon and germanium nanocrystals (NCs) are attractive materials owing to their unique size and surface-dependent optical properties. The optical properties of silicon and germanium NCs make them highly suitable for a range of applications, including bioimaging, light-emitting diodes, and solar cells. In this review, the solution synthesis, surface passivation, optical properties, biomedical applications, and cytotoxicity of silicon and germanium NCs are compared and contrasted. Over the last 10 years, synthetic protocols have improved considerably, with size control readily achieved. Investigations have begun into a range of silicon and germanium nanostructures, including doped, alloy, and metal-semiconductor hybrid NCs, which represent the next generation of silicon and germanium nanomaterials. Silicon and germanium NCs are actively researched for a wide array of biomedical applications, including, long-term in vivo cellular imaging, fluorescent nanocarriers for drug delivery, and as contrast agents for magnetic resonance imaging (MRI). Cytotoxicity studies have shown the low toxicity of Si NCs, while demonstrating that Ge NCs are less toxic than CdSe NCs at similar concentrations, giving these materials a strong future in nanomedicine applications.

Structural and optical properties of silicon metal-oxide-semiconductor light-emitting devices

A silicon p-channel metal oxide semiconductor field-effect transistor (Si-PMOSFET) that is fully compatible with the standard complementary metal oxide semiconductor process is investigated based on the phenomenon of optical radiation observed in the reverse-biased p–n junction in the Si-PMOSFET device. The device can be used either as a two-terminal silicon diode light-emitting device (Si-diode LED) or as a three-terminal silicon gate-controlled diode light-emitting device (Si gate-controlled diode LED). It is seen that the three-terminal operating mode could provide much higher power transfer efficiency than the two-terminal operating mode. A new solution based on the concept of a theoretical quantum efficiency model combined with calculated results is proposed for interpreting the evidence of light intensity reduction at high operating voltages. The Si-LED that can be easily integrated into CMOS fabrication process is an important step toward optical interconnects.

Optical functions of silicon from reflectance and ellipsometry on silicon-on-insulator and homoepitaxial samples

The optical properties of silicon have been determined from 0.2 to 6.5 eV at room temperature, using reflectance spectra of silicon-on-insulator (SOI) and ellipsometric spectra of homoepitaxial samples. Optimized Fabry-Perot-type SOI resonators exhibit high finesse even in near ultraviolet. Very high precision values of the real part of the refractive index are obtained in infrared up to a photon energy of 1.3 eV. The spectra of the extinction coefficient, based on observations of light attenuation, extend to 3.2 eV due to measurements on SOI layers as thin as 87 nm. These results allowed us to correct spectroellipsometric data on homoepitaxial samples for the presence of reduced and stabilized surface layers.

Electrophysical and optical properties of silicon produced by multiple remelting of metallurgical silicon by concentrated solar beams (Review)

The review describes a new method for refining silicon—multiple melting of industrial silicon in open air in a solar furnace. The results of three-, five- and eightfold refining are given. In all cases, a sample of melted silicon with simple ohmic contacts during heating at T > 30°C becomes a current and voltage generator, which is explained by the processes of self-organization of deep-lying impurities, leading to their periodic distribution along the sample. From such silicon, p–n transfer is obtained, which opens possibilities for practical application.

Annealing temperature and barrier thickness effect on the structural and optical properties of silicon nanocrystals/SiO2 superlattices

The effect of the annealing temperature and the SiO2 barrier thickness of silicon nanocrystal (NC)/SiO2 superlattices (SLs) on their structural and optical properties is investigated. Energy-filtered transmission electron microscopy (TEM) revealed that the SL structure is maintained for annealing temperatures up to 1150 °C, with no variation on the nanostructure morphology for different SiO2 barrier thicknesses. Nevertheless, annealing temperatures as high as 1250 °C promote diffusion of Si atoms into the SiO2 barrier layers, which produces larger Si NCs and the loss of the NC size control expected from the SL approach. Complementary Raman scattering measurements corroborated these results for all the SiO2 and Si-rich oxynitride layer thicknesses. In addition, we observed an increasing crystalline fraction up to 1250 °C, which is related to a decreasing contribution of the suboxide transition layer between Si NCs and the SiO2 matrix due to the formation of larger NCs. Finally, photoluminescence measurements revealed that the emission of the superlattices exhibits a Gaussian-like lineshape with a maximum intensity after annealing at 1150 °C, indicating a high crystalline degree in good agreement with Raman results. Samples submitted to higher annealing temperatures display a progressive emission broadening, together with an increase in the central emission wavelength. Both effects are related to a progressive broadening of the size distribution with a larger mean size, in agreement with TEM observations. On the other hand, whereas the morphology of the Si NCs is unaffected by the SiO2 barrier thickness, the emission properties are slightly modified. These observed modifications in the emission lineshape allow monitoring the precipitation process of Si NCs in a direct non-destructive way. All these experimental results evidence that an annealing temperature of 1150 °C and 1-nm SiO2 barrier can be reached whilst preserving the SL structure, being thus the optimal structural SL parameters for their use in optoelectronics.

The morphology and optical properties of silicon etched with bimetallic catalysts

The morphology and optical properties of silicon etched with bimetallic catalysts

Irradiation Enhancement of Electrical Properties of Passive Impurities in Silicon Crystals

Radiation defect formation processes in silicon crystals for the cases when concentrations of electrical nonactive impurities (oxygen, carbon) prevail over main impurities determining siliconconductivity, are being covered in this paper. The role of interstitial atoms and vacancies, oxygen and impurity atoms in formation of radiation defects of A - and E-centers and divacancies, as well as their influence on electrical and optical properties ofsilicon crystals are shown. Energy levels of radiation defects in forbidden gap of silicon and their introduction rates were defined based on temperature dependencies of the concentrations of charge carriers at different irradiation doses. The capture probability of interstitial atoms and vacancies by main and passive impurities is taking into account. In addition to known A -and E-centers, along with disordered regions (clusters), a new radiation centers with energetic levels at

Fabrication and optical properties of silicon nanowire/Cu2O nano-heterojunctions by electroless deposition technique

Si NWs/Cu2O nano-heterojunctions were prepared by adopting electroless deposition technique to deposit Cu2O nanocrystallines on the surface of silicon nanowire arrays (Si NWs). Raman spectra of the composite structures demonstrate that the infrared (IR) active mode originated from the defects in the crystal lattice and is activated in Cu2O nanocrystallines. Photoluminescence (PL) spectra of the nano-heterojunctions suggest that the as-prepared Si NWs/Cu2O composite structures present a new luminescence wavelength after the formation of nano-heterojunctions. In addition, the PL peak of Si NWs in the composite structure exhibits a little red-shift and becomes broad in comparison with that of the pure Si NWs. The radial Si NWs/Cu2O nano-heterojunction structure would have promising applications in many fields such as heterojuncion solar cell, photocatalysis, and water splitting hydrogen generation.

Optical properties of silicon with a high content of boron

After exposure of silicon with a high content of boron and oxygen to light with the spectrum close to that of solar radiation and with the intensity 70–80 mW cm−2, a new defect corresponding to the absorption band observed at liquid-helium temperature at the frequency 1026.7 cm−1 is detected in the material. It is shown that the components of the defect are boron and oxygen atoms. The defect is formed at a considerable concentration of free charge carriers induced by exposure of the sample to light or by heat treatments at a low current flow through the sample. It is thought that the defect can be formed due to the direct interaction between the components as well as via the precursors of the stable form of the defect. It is shown that doping of silicon with germanium reduces the efficiency of the formation of the defect corresponding to the detected absorption band.

Optical Properties of Silicon and Germanium Nanowire Fabric

The optical properties of free-standing nonwoven silicon (Si) and germanium (Ge) nanowire fabrics, including diffuse and specular reflectance, diffuse and direct transmittance, and absorptance spectra, were measured using an integrating sphere to account fully for all incident photons. Very thin, 50 μm thick, sheets with ∼90% void volume have extremely high optical densities. They are optically opaque across nearly all wavelengths from ultraviolet to near-infrared, and only minimal light penetrates when photon energies are below the band gap. The high optical density arises from a combination of scattering and absorption due to their high aspect ratio and narrow diameter as well as surface effects due to their very high surface area to volume ratio.

Effect of water adsorption on the structural and optical properties of silicon and titanium dioxide nanoclusters

The formation of the structure and infrared (IR) spectra of (SiO2)n (n = 1–4) and (TiO2)n (n = 1–3) clusters with an increase in their size n has been simulated using the B3LYP/6-31G* method of the density functional theory. The effect that water adsorption has on the structural and optical properties of silicon and titanium dioxide nanoclusters has been studied by this method as well. The calculated IR absorption bands for the structures of the (SiO2)n and (TiO2)n clusters are in good agreement with the bands observed in the IR spectra of the SiO2 and TiO2 films. It has been shown that the dissociative adsorption of the water occurs at the silicon centers, while the molecular form of adsorption is more energetically favorable at the active titanium centers. As a result of H2O adsorption, the electronic structure of TiO2 undergoes a transition from the semiconductor state to the dielectric one. The traces of water adsorbed at the titanium centers can be identified by the IR absorption spectra of samples due to a multiple (up to two orders of magnitude) increase in the intensities of the H2O molecule vibrations within the adsorption complex.

Control of the optical properties of silicon and chromium mixed oxides deposited by reactive magnetron sputtering

The development of mixed-oxide thin films allows obtaining materials with better properties than those of the different binary oxides, which makes them suitable for a great number of applications in different fields, such as tribology, optics or microelectronics. In this paper we investigate the deposition of mixed chromium and silicon oxides deposited by reactive magnetron sputtering with a view to use them as optical coatings with an adjustable refractive index. These films have been characterized by means of Rutherford backscattering spectrometry, Auger electron spectroscopy, X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy and spectroscopic ellipsometry so as to determine how the deposition conditions influence the characteristics of the material. We have found that the deposition parameter whose influence determines the properties of the films to a greater extent is the amount of oxygen in the reactive sputtering gas.

Structural and optical properties of silicon by tilted angle evaporation

We fabricate the silicon (Si) films on Si substrate by using the tilted angle evaporation technique. The deposition rate of Si films is decreased with increasing the tilted angle of substrate. The refractive index (n) and extinction coefficient can be engineered by the introduction of the porosity into Si films. The refractive index of Si films is controllably varied from 3.4 to 1.6 in the visible wavelength range for different incident angles of Si flux. The extinction coefficient also becomes lower for the larger tilted angle. The porous Si films (i.e., low-n Si) with an inclined nanocolumn structure are observed after evaporation, depending on the incident angle of Si flux. The reflectance of deposited Si films on Si substrate is measured by a spectrophotometer in comparison with theoretical calculations by rigorous coupled-wave analysis and transfer matrix method. These reflectance results are well consistent with the simulated results obtained using the measured refractive index values of the deposited Si films.