Near-surface Region Of Silicon Research Articles

X-Ray Diffraction and Raman Spectroscopy Analyses of GaSb-Enriched Si Surface Formed by Applying Diffusion Doping Technique

The paper studies the properties of surface and near-surface region of a single crystalline silicon sample doped with atoms of Ga (AIII) and Sb (BV). n-type single-crystal Si wafers were chosen as substrates, and samples were size of 8×10×0.5 mm3. For diffusion into silicon, Ga and Sb impurities were used with a purity of 99.999 and 99.998, respectively. The authors propose that a new heterostructure might form in the near-surface region of silicon that could be engineered by applying a relatively cheap diffusion method. The experimental and analysis results show that the composition and absorption spectrum of silicon start manifest certain changes, and can be used in the future as a functional material for solar cells. The result showed that randomly located islands with an average diameter of 1–15 µm are formed on the substrate surface. X-ray diffraction analysis was carried out using a Rigaku diffractometer to study the crystallographic parameters of islands formed with the participation of Ga and Sb atoms on the silicon surface. The energy spectrum was studied on Nanofinder High End Raman spectrometer (LOTIS TII) in order to determine the presence of complexes of Ga and Sb atoms within islands formed as a result of diffusion. The optical emission spectra in the new structure were studied using a Lambda 950 spectrophotometer. The measurements were carried out at room temperature, i.e., at 300°K. Having studied the results of X-ray analysis, Raman spectroscopy, and optical spectroscopy, the authors have revealed that Ga and Sb atoms form new Si0.44(GaSb)0.56 and Si0.75(GaSb)0.25-type binary compounds on Si surface.

FORMATION OF CRYSTALLINE SiC IN NEAR-SURFACE SILICON LAYERS BY METHOD OF COORDINATED SUBSTITUTION OF ATOMS

In this work, monocrystalline films of silicon carbide were synthesized on the surface of a Si(100) silicon wafer using the method of coordinated substitution of atoms. The films were synthesized at temperatures of 1200 °C and 1300 °C for 20 minutes in a CO gas flow at a pressure of 0.8 Pa. The effect of 1200–1300 °C temperatures on the formation of single- and polycrystalline layers, as well as nanostructured SiC phases in the near-surface region of silicon by the method of atom substitution, is analyzed. The formation of a high-quality crystalline silicon carbide film and the influence of synthesis conditions on the total volume of SiC structural phases, microstructure and nanostructure of the surface are shown. It was found that an increase in temperature from 1200 °C to 1300 °C led to a more intensive formation of silicon carbide and an increase in the number of Si–C bonds by 1.9 times due to an increase in the thickness of the synthesized silicon carbide layer. There is an increase in the proportion of the crystalline phase due to a more intense transformation of the nuclei of nanocrystals into micro- and nanocrystals. Intense processes of penetration of carbon atoms deep into silicon at a temperature of 1300 °C with amorphization of its structure and the formation of Si-C, which can transform into crystalline phases at temperatures above 1300 °C, are assumed. The proportion of the SiC crystalline phase increases to 50.2% of the film volume due to the intensive transformation of nanocrystal nuclei into micro- and nanocrystals. It has been experimentally shown that the formation of various SiC structures on Si (100) occurs in full accordance with the main principles of the method of coordinated substitution of atoms.

Features of silicon carbide synthesis by cold implantation of carbon recoil atoms

The Auger electron spectroscopy method confirmed a high concentration of carbon atoms (~ 85 at.%) introduced into silicon by cold implantation of recoil atoms. Carbon atoms are concentrated in a thin (~ 5 nm) near-surface region of silicon. Annealing of such a structure did not reveal a noticeable diffusion of carbon, which prevents obtaining a layer of SiC with a thickness of more than a few nm. This problem was solved by using radiation-enhanced diffusion. This made it possible to control the distribution profiles of carbon atoms in a wide range. Annealing at 1150oC allowed obtaining layers of amorphous-crystalline SiC with a thickness of 50-150 nm. Higher annealing temperatures are required to obtain a single-crystal SiC film. Keywords: cold implantation, radiation-enhanced diffusion, silicon carbide, recoil atom, thin films.

Особенности синтеза карбида кремния методом холодной имплантации атомов отдачи углерода

The Auger electron spectroscopy method confirmed a high concentration of carbon atoms (~ 85 at. % ), introduced into silicon by cold implantation of recoil atoms. Carbon atoms are concentrated in a thin (~ 5 nm) near-surface region of silicon. Annealing of such a structure did not reveal a noticeable diffusion of carbon, which does not allow obtaining a layer of SiC with a thickness of more than a few nm. The solution to this problem was carried out by the use of radiation-stimulated diffusion. This made it possible to control the distribution profiles of carbon atoms in a wide range. Annealing at 1150 oC allowed to obtain layers of amorphous crystalline SiC with a thickness of 50-150 nm. Higher annealing temperatures are required to obtain a single-crystal SiC film.

Physical foundations of the formation of the silicon-based heterovarizonic structure

With the formation of binary unit cells based on the AII and BVI, AIII and BV elements, a heterovarizonic structure was obtained in the near-surface region of silicon, without destroying the crystal structure, without surface states with a thickness of about 5 μm. The resulting heterovarizonic structure has special fundamental parameters that ensure the absorption of light in a wide range of the solar spectrum from UV to IR radiation with λ=0.1-3 μm, i.e., it covers the entire solar spectrum. Keywords: silicon, photocell, solar cell, heterovarizonic structure, photovoltaics, AIIBVI, AIII, BV compounds.

Физические основы формирования гетероваризонной структуры на основе кремния

With the formation of binary unit cells based on the AII and BVI, AIII, and BV elements, a heterovarizonic structure was obtained in the near-surface region of silicon, without destroying the crystal structure, without surface states with a thickness of about 5 μm. The resulting heterovarizonic structure has special fundamental parameters that ensure the absorption of light in a wide range of the solar spectrum from UV to IR radiation with λ = 0.1-3 μm, i.e., it covers the entire solar spectrum.

Using MoOx/p-Si Selective Contact for Evaluation of the Degradation of a Near-Surface Region of Silicon

Using MoOx/p-Si Selective Contact for Evaluation of the Degradation of a Near-Surface Region of Silicon

Исследование радиационных эффектов в МОП-транзиcторе с p-каналом

The effect of gamma radiation on the formation of surface defects at the Si−SiO2 interface in a MOS transistor with a p-channel in the passive mode is considered. Several surface defect formation processes were observed. The role of molecular hydrogen in the gate oxide of the MOS transistor and ”hot“ electrons formed in the near-surface region of silicon is shown.

Studying Evolution of the Ensemble of Micropores in a SiC/Si Structure during Its Growth by the Method of Atom Substitution

The time evolution of the ensemble of micropores formed in the near-surface region of silicon during the growth of thin films of silicon carbide is studied by the method of atom substitution. SiC/Si samples are studied by scanning electron microscopy, ellipsometry, and confocal Raman microscopy. The formation of the porous layer involves several characteristic stages: the emergence of single pores, their growth with the formation of dendrite-like structures, and subsequent coalescence into a continuous layer. It is shown that the thickness of the porous layer at the initial stages of the growth is proportional to the cubic root of time. The possible mechanisms of pore formation are discussed and a theoretical model is proposed to describe the dependence of the average thickness of the porous layer on time. The model is in a good qualitative agreement with the experimental results.

Эволюция ансамбля микропор в структуре SiC/Si в процессе роста методом замещения атомов

AbstractThe time evolution of the ensemble of micropores formed in the near-surface region of silicon during the growth of thin films of silicon carbide is studied by the method of atom substitution. SiC/Si samples are studied by scanning electron microscopy, ellipsometry, and confocal Raman microscopy. The formation of the porous layer involves several characteristic stages: the emergence of single pores, their growth with the formation of dendrite-like structures, and subsequent coalescence into a continuous layer. It is shown that the thickness of the porous layer at the initial stages of the growth is proportional to the cubic root of time. The possible mechanisms of pore formation are discussed and a theoretical model is proposed to describe the dependence of the average thickness of the porous layer on time. The model is in a good qualitative agreement with the experimental results.

Optička svojstva monokristalnog silicijuma implantiranog nisko-energetskim jonima srebra

The present paper investigates the effects of low-energy silver ions implantation on the optical properties of monocrystalline silicon. Si(100) wafers were implanted with 60 keV Ag ions, to the fluences in the range of 1×1013-1×1016 ions/cm2. Composition of the implanted Si samples was analysed by means of Rurherford backscattering spectrometry and the optical spectra were obtained by spectroscopic ellipsometry measurements. The results revealed that the Ag ions are situated in the near-surface region of silicon, at depths of ~ 36 nm. When ion fluence of Ag ions was increased the concentration of Ag was also increased and for the highest ion fluence of 1×1016 ions/cm2 reach the value of ~ 6 at.%. At the fluence of 1×1014 ions/cm2 a strong apsorption in the optical spectra has been observed, which is associated with the excitation of surface plasmon resonance (SPR) of Ag nanoparticles. The position of the SPR peak shifted in the range of 326-1300 nm when the Ag ion fluence was varied up to 1×1016 ions/cm2. The results suggest that for higher implantation fluences the interaction between the Ag nanoparticles become important parameter which dominate the surface plasmon resonance effect of silver in Si.

On the synthesis of nanoscale phases of metal silicides in the near-surface region of silicon and the study of their electronic structures by passing light

The band gap E g of nanocrystalline phases NaSi2 and CoSi2 synthesized on the surface and in the near-surface region of silicon by ion implantation in combination with annealing is determined by measuring the intensity of light at different frequencies, passing through the test samples, and by using ultraviolet photoelectron spectroscopy. The nanoscale phases MeSi2 (Me = Na, Co) on the surface of silicon are obtained by the implantation of Me ions with the energy E 0 = 1 keV; and in the near-surface region (at a depth of 15–16 nm), by the implantation of ions with E 0 = 15 keV. Postimplantation annealing is mainly carried out by heating. It is shown that MeSi2 nanocrystalline phases both on the surface and in the near-surface layer are crystallized in the cubic lattice. It is found that E g of the nanocrystalline metal-silicide phases, depending on their size, can range from 0.6 to 1 eV.

10.1007/s11453-008-3002-9

A quantitative model for near-surface redistribution of doping impurity in silicon in the course of proton-stimulated diffusion is developed for the first time. According to the model, the near-surface peak of the impurity concentration is caused by migration of neutral impurity—self-interstitial pairs to the surface with subsequent decomposition of these pairs and accumulation of the impurity at the silicon surface within a thin layer (referred to as δ-doped layer). The depletion and enhancement regions that are found deeper than the near-surface concentration peak are caused by expulsion of ionized impurity by an electric field from the near-surface region of the field penetration. The field appears due to the charge formed in the natural-oxide film at the silicon surface as a result of irradiation with protons. The diffusion-kinetic equations for the impurity, self-interstitials, vacancies, and impurity—self-interstitial pairs were solved numerically simultaneously with the Poisson equation. It is shown that the results of calculations are in quantitative agreement with experimental data on the proton-stimulated diffusion of boron impurity in the near-surface region of silicon.

Two-stage doping of silicon with phosphorus-32 and sulfur-32 isotopes

We describe a principally new approach to obtaining solid sources of sulfur for the two-stage diffusion doping of silicon, which eliminates the surface erosion of wafers. According to the proposed method, 32P radionuclide is diffused into a near-surface region of silicon in the first (introduction) stage and then converted into 32S isotope in the second state. It is shown that the samples of silicon doped by this method with 32S isotope contain deep levels with the ionization energies Ec − 0.13 eV, Ec − 0.25 eV, Ec − 0.37 eV, and Ec − 0.50 eV, which exhibit a donor character and are related to the sulfur impurity. It is established that the diffusion of 32S isotope into p-Si leads to a change in the type of conduction, while the diffusion of this isotope into n-Si decreases the resistivity of the initial material.

Simulation of near-surface proton-stimulated diffusion of boron in silicon

A quantitative model for near-surface redistribution of doping impurity in silicon in the course of proton-stimulated diffusion is developed for the first time. According to the model, the near-surface peak of the impurity concentration is caused by migration of neutral impurity—self-interstitial pairs to the surface with subsequent decomposition of these pairs and accumulation of the impurity at the silicon surface within a thin layer (referred to as δ-doped layer). The depletion and enhancement regions that are found deeper than the near-surface concentration peak are caused by expulsion of ionized impurity by an electric field from the near-surface region of the field penetration. The field appears due to the charge formed in the natural-oxide film at the silicon surface as a result of irradiation with protons. The diffusion-kinetic equations for the impurity, self-interstitials, vacancies, and impurity—self-interstitial pairs were solved numerically simultaneously with the Poisson equation. It is shown that the results of calculations are in quantitative agreement with experimental data on the proton-stimulated diffusion of boron impurity in the near-surface region of silicon.

Simulation of current–voltage characteristics of a MOS structure considering the tunnel transport of carriers in semiconductor

The effect of a tunnel charge transport in the near-surface region of silicon on the electrical characteristics of MOS structures with a 2–3 nm insulator layer is studied theoretically. An equilibrium condition for the substrate is assumed. The cases of an Al and polySi gate are considered. The possibility of a ‘double’ (in Si and through SiO2) tunnelling expands the energy range of transported particles, which increases one of the components of the total tunnel current. The proposed model allows for the improved simulation of gate current in MOSFETs, which is especially important for highly-doped substrates.

Ultrafast transient grating scattering studies of carrier dynamics at a silicon surface

Transient grating scattering, in the reflective configuration, is used to study the dynamics of photoexcited carriers in the near-surface region of silicon on femtosecond and picosecond time scales. A rich variety of carrier relaxation processes including carrier dephasing, energy relaxation, and ambipolar diffusion are manifested in the grating scattering signal. Strong dependence of relaxation and diffusion rates on carrier concentration, reflecting the effects of charge screening at higher carrier concentrations, has been observed.

Correlation of Electric Parameters Change and Structural Changes Induced in Silicon Systems by Pulsed Magnetic Field Treatment

AbstractThe results of comparison investigations of structural and electric parameters changes in silicon systems induced by pulsed magnetic field (MF) treatment (PMFT) are presented for the first time. The characteristics of (PMFT) that can induce considerable parameters changes of the silicon system were determined. Amplitudc of thc magnctic impulscs is 0.1-0.3 MA/m and duration of thc impulscs is 10-30 ms. The investigations were carried out by means of scanning electron microscope (SEM), X-ray diffraction analysis, C-V and DLTS spectroscopies. The PMFT induces the generation of A-centers in the near-surface region of silicon, the changes of the crystal lattice parameter and the concentration of free electrons and results in emergence of an extent structural microdefects in subsurface. The obtained experimental data testifies that PMFT is possible to increase the vacancy concentration at subsurface region of silicon.

Angular dependence of silicon oxide formation and gold segregation due to low-energy O 2+ implantation

High-resolution Rutherford backscattering spectrometry was used to investigate the effect of the angle of incidence on the composition of silicon bombarded with 4 keV O 2 + ions. The redistribution of gold impurities, initially present as a thin surface layer, was studied simultaneously. Complete oxidation, i.e. the formation of SiO 2, could be achieved at impact angles between 0° and 30° to the surface normal. Assuming a density equivalent to that of thermally grown oxides, the thicknesses of the oxides generated by implantation were found to range from 13 nm (0°) to 10 nm (30°). At impact angles exceeding 30° the near-surface region of silicon was only incompletely oxidized to SiO x , with x < 2. Comparison with the angular dependence of the silicon sputtering yield Y suggests that complete oxidation is achieved at angles where Y < 0.5 Si atoms per O atom. At angles above 60° the oxidation state appeared to be enhanced owing to the incorporation of oxygen from the residual gas, the effect being noticeable because of moderate working pressures and relatively low mean current densities. This supposition was substantiated by studying oxygen incorporation during bombardment with 4 keV Xe + ions. The gold impurities were found to segregate on the large-depth side of the SiO 2 layer generated by oxygen implantation. O 2 + bombardment of a fully oxidized layer at 45° showed that the internal profile of the segregated gold atoms largely retains its shape while being shifted towards the sputter-eroded surface.

Formation Mechanism and Recombination-Enhanced Dissociation of a Hydrogen-Carbon Complex in Silicon

ABSTRACTWc have found that chemical etching induced an electron trap E3 (0.15) into n-typc Si. We attribute this trap to a hydrogen-carbon complex on the basis of available experimental data. By measuring DLTS depth profiles of the E3 trap, we propose a model of the formation mechanism of the hydrogen-carbon complex as follows. Hydrogen atoms arc adsorbed on the Si surface to terminate Si dangling bonds during chemical etching, and after the etching some unstably adsorbed ones diffuse into the near-surface region of silicon and are trapped by carbon to form the complex. The E3 trap is stable up to 100δC in the dark but is annihilated by the illumination of band gap light around 250K only outside the depletion layer of the Schottky structure. This provides unambiguous experimental evidence for the recombination-enhanced dissociation, in which the electronic energy released by the electron-hole recombination at the E3 level is converted into local kinetic energy of hydrogen to be released from carbon.