Optical characterization of laser-induced crystallized silicon films

Optical absorption coefficient spectra of thin silicon films were precisely investigated using a simple reflectance system with total reflectance mirrors placed on the rear side of samples in order to cancel an interference effect in a range between 1.1 eV and 3 eV. The absorption coefficient decreased according to crystallization as the laser energy increased and it got similar to that of single crystalline silicon in the range of 1.7 eV 3 eV. However, the absorption coefficient was higher than 10² cm^–1 in the photon energy lower than 1.3 eV. This probably results from band tail states caused by defect states localized at grain boundaries in the crystallized films. 2.5%-phosphorus doped laser crystallized silicon films had a high optical absorption coefficient ( > 10⁴ cm^–1) in the low photon energy range (1.1 eV 1.7 eV) caused by free carriers produced from the dopant atoms activated in the silicon films. The experimental results gave the carrier density of 1.3 × 10²¹ cm³ and the carrier mobility of 20 cm²/Vs.     

致冷多层干涉滤光片的光学特性

本文系统地研究了红外多层干涉滤光片的低温特性、并从薄膜的基本光学特性出发,推导了窄带滤光片、截止滤光片透射率与波长的温度效应.给出了截止滤光片截止波长的温度漂移公式.     

X-ray photoelectron spectroscopy characterization of stain-etched luminescent porous silicon films

The surface and in-depth chemical nature of the photoluminescent stained Si layer obtained with a novel procedure based on HF/HNO₃ is presented. Oxide-free porous Si surfaces result from controlled preparation, storing and handling of samples, as revealed by parallel X-ray photoelectron spectroscopy and X-ray-induced Auger electron spectroscopy measurements, coupled with Ar⁺ ion sputtering. The present findings support the model for the porous layer of oxidized samples of Si grains embedded in a silica gel matrix.     

Optical properties of porous silicon

We have measured the absorption spectra and the dispersion of refractive index for porous silicon samples with different porosities in the energy range 1.5–3.5 eV at room temperatures. The experimental data are compared with the dependences calculated by using Bruggeman’s theory for the dielectric constant of a multicomponent system composed of crystal silicon, SiO₂, amorphous silicon, and voids (pores). The best agreement between the experimental and theoretical dependences is achieved for a significant percentage of SiO₂ in the porous silicon samples.     

Cathodoluminescence from nanocrystalline silicon films and porous silicon

Received: 4 May 1998 / Accepted: 30 October 1998     

Optical characteristics of porous silicon structures

Morphology, composition, and optical properties of porous silicon on single-crystal-silicon substrates and p-n junctions are studied. Substrate orientation, type of conduction, and composition of etching agent are varied to obtain nano-, meso-, and microporous silicon and multilayer porous structures. A correlation of the photoluminescence intensity and intensity of the IR absorption band peaking at 616 cm^?1 is related to the presence of Si-Si bonds.     

Enhanced Raman scattering in multilayer structures of porous silicon

Multiple enhancement of the Raman scattering efficiency is observed in porous‐silicon‐based one‐dimensional photonic bandgap (PBG) structures with tunable reflection and dispersion under excitation at 1.06 µm. The experimental results are explained as being due to the resonant increase in the effective Raman susceptibility at light wavelengths close to the PBG edges. This effect is discussed in view of possible applications in the Raman spectroscopy of molecules embedded in porous media as well as in the Raman laser based on silicon. Copyright © 2011 John Wiley & Sons, Ltd.     

Reflection characterization of multilayer surface films

The reflection of linearly polarized light from a multilayer system of ultrathin dielectric surface films is investigated both analytically in the long-wavelength limit and numerically by the standard way of calculating the reflection characteristics for the layered medium. The second-order approximate formulas for reflection coefficients and characteristic reflection angles are derived and their accuracy is estimated. It is shown that approximate expressions obtained for reflection parameters of multilayer system in the long-wavelength limit are of immediate interest to the solution of the inverse problem for ultrathin layered surface structures. Innovative possibilities for optical diagnostics are generated by means of polarizing and principal angles. For determining the parameters of multiple surface layers an appropriate method is found by combining differential reflectance with ellipsometry.     

Optical properties of erbium-doped porous silicon waveguides

Planar and buried channel porous silicon waveguides (WG) were prepared from p⁺-type silicon substrate by a two-step anodization process. Erbium ions were incorporated into pores of the porous silicon layers by an electrochemical method using ErCl₃-saturated solution. Erbium concentration of around 10²⁰ at/cm³ was determined by energy-dispersive X-ray analysis performed on SEM cross-section. The luminescence properties of erbium ions in the IR range were determined and a luminescence time decay of 420 μs was measured. Optical losses were studied on these WG. The increased losses after doping were discussed.     

Optical characteristics of implanted silicon films

The first data are presented on the change (following implantation) in the refractive index and the band structure of silicon on sapphire films. The implantation was effected with phosphor ions of 40 keV and doses from 10¹² to 10¹⁶ cm^–2. An increase following implantation of the refractive index and the energy of the first direct allowed transitions E₁ is noted, indicating changes in the second coordination sphere. The profile E₁(x) is studied pointing to heterogenization effects. The films were annealed with ruby laser pulses of 0.2 J/cm². The same laser was used to study the lux dependence of the injection level _n and surface photo-emf V. Hysteresis in the V(_n) dependence (after the use of maximum intensity of the laser beam) is noted indicating irreversible straightening of the bands at the film surface.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 40–43, May, 1984.     

Fractal microstructures of light-emitting porous silicon films

By means of scanning electron microscopy and computer simulation, we have investigated the microstructures of a 23-μm-thick porous silicon (PS) film and a 6-μm-thick PS film. The two films give off strong visible emissions when excited by the 254 nm light. For the 23-μm-thick PS film, both of its cross-sectional and top-surface morphologies exhibit self-similarity whose small-scale and large-scale microstructures resemble one another. For the 6-μm-thick PS film, self-similar cracks are developed on its top surface. Our results have demonstrated that the microstructures of PS films exhibit the characteristics of fractals. With box counting method, the fractal dimensions of the PS films are calculated to be about 2.3-2.6. Based on the model of diffusion-limited aggregation, the fractal growth processes have been simulated for the PS films.     

Tuning the cathodoluminescence of porous silicon films

We have obtained intense cathodoluminescence (CL) emission from electron beam modified porous silicon films by excitation with electrons with kinetic energies below 2 keV. Two types of CL emissions were observed, a stable one and a non-stable one. The first type is obtained in well-oxidized samples and is characterized by a spectral peak that is red shifted with respect to the photoluminescence (PL) peak. The physically interesting and technologically promising CL is however the CL that correlates closely with the PL. Tuning of this CL emission was achieved by controlling the average size of the nanostructure thus showing that the origin of this CL emission is associated with the quantum confinement and the surface chemistry effects that are known to exist in the porous silicon system. We also found that the electron bombardment causes microscale morphological modifications of the films, but the nanoscale features appear to be unchanged. The structural changes are manifested by the increase in the density of the nanoparticles which explains the significant enhancement of the PL that follows the electron irradiation.     

Optical characterization of thin silicon films deposited by CVD and annealed by pulsed laser

Polycrystalline Si layers 100 to 800 nm thick have been deposited on Si single crystal substrates by CVD and annealed with a Q-switched ruby laser at energies up to 1.5 J/cm². The optical characteristics of these layers have been measured by SEM and ellipsometry. The results can be attributed to a change in surface roughness with film thickness and laser energy.     

Optical constants of titanium and silicon dioxide films

In this paper a study of optical constants of titanium and silicon dioxide films prepared in Balzers BAK 600 and BA 510 conventional high-vacuum apparatus is described. Both the dispersion and the geometrical thickness were determined from normal reflectance spectrum by adapted general algorithm of the statistical interpretation of measured data. The dependence of optical constants on oxygen pressure for both materials and the evaporation rate dependence for titanium dioxide were obtained. The time changes of these constants were also measured.     

Growth and properties of PbTe films on porous silicon

The structural and electrical characteristics of vacuum deposited PbTe films on Si substrate with buffer porous silicon (PS) layer were investigated. Auger electron spectroscopy, electron and optical microscopy data have shown the absence of cracks, pores, metal and chalcogen microinclusions. A mosaic structure with a grain size of 20–60 μm was detected by selective chemical etching and acoustic microscopy methods. The investigations of X-ray diffraction and X-ray pole figures showed that grains have [100] orientation along the growth direction. The cooling–heating (300–77–300 K) cycles of multilayer PbTe/sublayer/Si structures did not lead to the processes of peeling or appearance of cracks. It was found that thick amorphous layers on a PS surface change the nature of PbTe films growth.     

Optical measurements of oxide films on silicon

The optical constants of oxide films formed by heating single-crystal silicon specimens were measured. The measurements were carried out in a range of 300° to 1000°C. The thickness and refractive indices of the oxide films were determined by the polarimetric method. In the measured temperature interval the oxidation process can be divided into three groups. In the first range, from 300° to 560°C, no oxidation of the silicon surface was observed. In the second interval, from 560° to 950°C, the oxidation of silicon proceeded according to the linear oxidation law. At temperatures from 950° to 1000°C the thickness of the oxide films increased with the square root of the heating time according to the parabolic oxidation law.     

Optical properties of neodymium incorporated in porous silicon

We report the optical properties of Nd-incorporated porous silicon. Photoluminescence and photoluminescence excitation measurements have been performed. Room temperature emission spectra from dried or annealed samples have been studied. While steady-state photoluminescence results indicate porous silicon light absorption by the Nd, the photoluminescence excitation shows a deficiency of energy transfer between porous silicon and Nd ions.     

On the morphology of stain-etched porous silicon films

Morphology of stain-etched porous silicon films was investigated by a non-destructive technique, based on reflectance spectrometry: dielectric function profiles were computed by spectral reflectance via a finite difference model, and porosity was deduced by the effective medium approximation. Theoretical calculations were supported by high-resolution electron microscopy observations. The relations among oxidising species concentration in the etching solution, porosity profile and surface reflectance of the films were investigated.