Silicon Samples Research Articles

Structure Determination and Defect Analysis n-Si<Lu>, p-Si<Lu> Raman Spectrometer Methods

In this work, lutetium-doped silicon samples were studied using the Raman scattering method. Registration and identification of both crystalline and amorphous phase components in the samples was carried out. There is some violation in the spectra of Raman scattering of light samples of silicon doped with lutetium in comparison with the original sample. It was found that the intensity of Raman scattering of doped samples is 2-3 times higher than the scattering from silicon. The comparison is carried out for the intensities associated with the intensities of the single-phonon line of the silicon substrate. This effect of the Raman spectra in the range 930 cm‑1 – 1030 cm–1 appearing in this range is similar to the data reduction for multiphonon propagation on silicon. For the obtained images (n-Si<Lu> and p-Si<Lu>), the bands in the atomic range of combinatorial scattering have a mixed broad and oval background in the range from 623 cm-1 to 1400 cm-1. This background can change the shape of the observed bands.

Lateral Photoelectric Effect In Iron-Silicon Dioxide-Compensated Silicon Hybrid Structures

This article presents experimental results on the technology of obtaining and studying the lateral photoelectric effect (LPE) in hybrid structures (HS) of the Fe/SiO2/p-Si<B, Mn> and Fe/SiO2/n-Si<B, Mn> types. The technology for obtaining such HS consists of two parts: firstly, obtaining compensated (C), highly compensated (HC), and over-compensated (OC) samples of Si <B, Mn>. Secondly, obtaining HS Fe/SiO2/p-Si<B, Mn> and Fe/SiO2/n-Si<B, Mn>. Based on the results, it is shown that sufficiently good HS has been obtained. Experiments on the study of LPE have shown that in the studied HS there is a pronounced manifestation of the lateral photoelectric effect, the magnitude and nature of which strongly depend on the type of conductivity and resistivity of the compensated silicon. The observed features are explained by the fact that in С, HC, and OC silicon samples, impurities that create deep levels in the silicon band gap form various multi-charged complexes that modulate the energy band of silicon, which lead to significant changes in its physicochemical and generation-recombination properties, which underlies the observed effects. Based on the LPE studies, depending on the contact distance, it is possible to determine the numerical values of the diffusion lengths of the minor current carriers (Lp and Ln), their lifetimes (τp and τn), and diffusion coefficients (Dp and Dn) on the substrate material.

Effect of laser fluence on the optoelectronic properties of nanostructured GaN/porous silicon prepared by pulsed laser deposition

In this study, the fabrication of nanostructured GaN/porous Si by pulsed laser deposition (PLD) was demonstrated. The porous silicon was prepared using laser-assisted electrochemical etching (LAECE). The structural, optical, and electrical properties of GaN films were investigated as a function of laser fluence. XRD studies revealed that the GaN films deposited on porous silicon were nanocrystalline, exhibiting a hexagonal wurtzite structure along the (100) plane. Spectroscopic property results revealed that the photoluminescence PL emission peaks of the gallium nitride over porous silicon (GaN/PSi) sample prepared at 795 mJ/mm2 were centered at 260 nm and 624 nm. According to topographical and morphological analyses, the deposited film consisted of spherical grains with an average diameter of 178.8 nm and a surface roughness of 50.61 nm. The surface of the prepared films exhibited a cauliflower-like morphology. The main figures of merit of the nanostructured GaN/P-Si photodetectors were studied in the spectral range of 350–850 nm. The responsivity, detectivity, and external quantum efficiency of the photodetector at 575 nm under − 3 V were 19.86 A/W, 8.9 × 1012 Jones, and 50.89%, respectively. Furthermore, the photodetector prepared at a laser fluence of 795 mJ/mm2 demonstrates a switching characteristic, where the rise time and fall time are measured to be 363 and 711 μs, respectively.

XPS Study of the Preparation of Single-Site Catalysts Based on Ir(I) and Rh(I) Complexes Immobilized on a SiO<sub>2</sub> Surface Using a P-Containing Linker

Samples of model single-site iridium and rhodium catalysts were synthesized by immobilization of complexes [Ir(COD)(IMes)Cl] and [Rh(COD)(IMes)Cl], where COD is cyclooctadiene-1,5 and IMes is 1,3‑bis(2,4,6-trimethylphenyl)imidazol-2-ylidene, on the surface of silicon dioxide modified with a linker containing diphenylphosphine group (Ph2P). Silicon plates with a flat surface covered with a layer of natural oxide 1–3 nm thick, Si-SiO2(nat), or with a specially grown SiO2 film (∼300 nm), Si-SiO2(ox), were used as supports. The chemical compositions of the surface of the modified silicon plates and samples of model catalysts were characterized by XPS. Based on these XPS studies, a tentative conclusion was made about the coordination of immobilized complexes to the SiO2 surface. Catalyst samples were tested in the gas-phase hydrogenation of propene with parahydrogen.

Multi-Wavelength Angle-Resolved Scattering of Randomly Rough Surfaces Based on the Scalar Diffraction Theory

Angle-resolved scattering was measured for four samples of silicon exhibiting different surface roughnesses. The measurements were performed for three wavelengths: 457.9 nm, 514.5 nm, and 647.1 nm. Three approaches were used to evaluate the experimental data. The first approach corresponds to the exact formula derived using the scalar diffraction theory. This formula is quite complicated, and numerical methods must be used for its evaluation. For this reason, another two approaches representing approximations by much simpler formulae were considered. The use of several wavelengths allowed us not only to recover the power spectral density function in a limited interval of spatial frequencies but also to determine the total rms values of the heights, which represent the quantity of roughness for all spatial frequencies. The possibility of recovering the total rms values of the heights using the multi-wavelength approach is the most important result of this work. The results obtained from the scattering experiment and atomic force microscopy are compared.

Rapid sensing of hidden objects and defects using a single-pixel diffractive terahertz sensor

Terahertz waves offer advantages for nondestructive detection of hidden objects/defects in materials, as they can penetrate most optically-opaque materials. However, existing terahertz inspection systems face throughput and accuracy restrictions due to their limited imaging speed and resolution. Furthermore, machine-vision-based systems using large-pixel-count imaging encounter bottlenecks due to their data storage, transmission and processing requirements. Here, we report a diffractive sensor that rapidly detects hidden defects/objects within a 3D sample using a single-pixel terahertz detector, eliminating sample scanning or image formation/processing. Leveraging deep-learning-optimized diffractive layers, this diffractive sensor can all-optically probe the 3D structural information of samples by outputting a spectrum, directly indicating the presence/absence of hidden structures or defects. We experimentally validated this framework using a single-pixel terahertz time-domain spectroscopy set-up and 3D-printed diffractive layers, successfully detecting unknown hidden defects inside silicon samples. This technique is valuable for applications including security screening, biomedical sensing and industrial quality control.

Interplay between facetting and confinement in directional solidification of silicon: A direct comparison between experiments and phase-field simulations

We combine the analysis of experiments based on in situ X-ray imaging and phase-field simulations to get insight into the interplay between faceting and confinement effects in thin silicon samples during directional solidification from a monocrystalline seed. The phase-field model is parametrized by available experimental results, especially regarding the anisotropy functions for the surface energy and for the kinetic attachment coefficient. In the present work, a method is proposed to extrapolate 2D fully quantitative simulations results to 3D thin sample geometry. Two simple seed orientations along the 〈110〉 and 〈100〉 crystal directions are considered. For 〈110〉 direction, it is shown that confinement effects are weak so 2D simulations can be readily compared to the experiments. For 〈100〉 direction, much stronger confinement effects are identified and characterized by a confinement factor that is estimated from phase-field simulations of thin 3D systems. For both directions, the length of the side facets is shown to increase with the solidification velocity and an analytical expression including the confinement factor is obtained for the law relating both quantities. A very quantitative experiment-simulation agreement is obtained in each case.

PROCESSES OF DEFECT FORMATION IN SILICON DIFFUSIONALLY DOPED WITH PLATINUM AND IRRADIATED WITH PROTONS

In this work, we studied the effect of technological regimes and proton implantation on the processes of defect formation in single-crystal n-type silicon (n-Si) doped with platinum using the method of impedance spectroscopy. It has been established that radiation-induced changes in the electrical conductivity of silicon depend significantly on the technological regimes of doping with impurities in silicon. Hodographs show that doping with platinum leads to a decrease in the electrical resistance of silicon samples. Irradiation with 2 MeV protons at a dose of 5.1 × 1014 particles / cm2 leads to a significant (2-3 times) increase in the electrical resistance of the silicon samples under study. It is concluded that the relatively high resistance to radiation exposure (resistance change of no more than 16%: from 55 kΩ to 65 kΩ as a result of ion implantation) of samples doped at 1200°C is presumably due to a higher concentration of impurity ions (platinum) in the samples volume compared to 1100°C.

Mechanisms of Current Transition in High Compensated Silicon Samples with Zinc Nanoclusters

This article presents experimental results on the study of the current-voltage characteristics of strongly compensated n- and p-type silicon samples diffusion-doped with zinc at a temperature of 80 K. The current-voltage characteristics of the studied samples contain both sublinear and superlinear sections. Several (up to eight) characteristic areas were found, the number of which depends on the degree of illumination, temperature, and electrical resistivity of the sample. Under certain conditions, there is an alternation of sections of the current-voltage characteristic with negative differential conductivity of the N- and S-type, behind which current instabilities with an infra-low frequency are observed. The appearance of sections of the current-voltage characteristic with a quadratic dependence is explained by the presence of fast and slow recombination centers associated with zinc nanoclusters, and sublinear sections are explained in terms of the theory of the "injection depletion effect". The formation of nanoclusters with the participation of zinc ions was confirmed by atomic force microscopy studies.

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.

A Surface Study of Si Doped Simultaneously with Ga and Sb

The paper is concerned with the study of silicon samples doped with gallium (Ga) and antimony (Sb) atoms. In particular, the elemental analysis, SEM imaging, and Raman spectrometry analysis of the samples are presented. The elemental analysis revealed that the relative concentrations of Ga (0.4) were almost equal to those of Sb (0.39) and both were formed on the surface of Si. The SEM imaging showed that GaSb microsized islands (diameter of 1 to 15 microns) and a density of ~106 cm-2 were being formed on the surface of Si in the course of the process of diffusion doping. Raman spectral analysis showed that a semiconductor with GaSb molecules self-assemble on Si surface.

Investigation of Defect Formation in Silicon Doped with Silver and Gadolinium Impurities by Raman Scattering Spectroscopy

Silicon doped with gadolinium and silver impurities were studied using a Renishaw InVia Raman spectrometer. Registration and identification of both crystalline and amorphous phase components in the samples was carried out. Some changes are observed in the Raman spectra of gadolinium-doped silicon samples compared to the initial sample. It has been experimentally found that an increase in the silver impurity concentration in gadolinium-doped silicon leads to a smoothing of the Raman spectrum, which indicates the formation of a more perfect crystal structure.

Ultralow-energy amorphization of contaminated silicon samples investigated by molecular dynamics.

Ion beam processes related to focused ion beam milling, surface patterning, and secondary ion mass spectrometry require precision and control. Quality and cleanliness of the sample are also crucial factors. Furthermore, several domains of nanotechnology and industry use nanoscaled samples that need to be controlled to an extreme level of precision. To reduce the irradiation-induced damage and to limit the interactions of the ions with the sample, low-energy ion beams are used because of their low implantation depths. Yet, low-energy ion beams come with a variety of challenges. When such low energies are used, the residual gas molecules in the instrument chamber can adsorb on the sample surface and impact the ion beam processes. In this paper we pursue an investigation on the effects of the most common contaminant, water, sputtered by ultralow-energy ion beams, ranging from 50 to 500 eV and covering the full range of incidence angles, using molecular dynamics simulations with the ReaxFF potential. We show that the expected sputtering yield trends are maintained down to the lowest sputtering yields. A region of interest with low damage is obtained for incidence angles around 60° to 75°. We also demonstrate that higher energies induce a larger removal of the water contaminant and, at the same time, induce an increased amorphization, which leads to a trade-off between sample cleanliness and damage.

Comprehensive Investigation of Constant Voltage Stress Time-Dependent Breakdown and Cycle-to-Breakdown Reliability in Y-Doped and Si-Doped HfO2 Metal-Ferroelectric-Metal Memory.

In this study, we comprehensively investigate the constant voltage stress (CVS) time-dependent breakdown and cycle-to-breakdown while considering metal-ferroelectric-metal (MFM) memory, which has distinct domain sizes induced by different doping species, i.e., Yttrium (Y) (Sample A) and Silicon (Si) (Sample B). Firstly, Y-doped and Si-doped HfO2 MFM devices exhibit domain sizes of 5.64 nm and 12.47 nm, respectively. Secondly, Si-doped HfO2 MFM devices (Sample B) have better CVS time-dependent breakdown and cycle-to-breakdown stability than Y-doped HfO2 MFM devices (Sample A). Therefore, a larger domain size showing higher extrapolated voltage under CVS time-dependent breakdown and cycle-to-breakdown evaluations was observed, indicating that the domain size crucially impacts the stability of MFM memory.

A unique sustainable chemical method for the recovery of pure silicon from waste crystalline silicon solar panels

The present work suggests a unique approach for recovering pure silicon from end-of-life silicon solar panels by a direct treatment which does not involve the use of Hydrofluoric Acid (HF). Firstly, the better alkaline treatment between NaOH and KOH was determined. Then, effects of HF etching time and concentration were studied by comparing different etching treatments. Metal impurities such as Ag, Sn, and heavy metal Pb decreased considerably during the acid leaching studies with suitable concentrations. The major impurity Aluminium was reduced significantly by a two-step chemical treatment which ensures minimal silicon loss. Although it is possible to recover 4 N pure silicon by both (with and without HF etching) methods, direct treatment is preferred since the process eliminates potential human health and environmental concerns associated with HF. The recovered silicon samples were analysed by ICP-OES to detect impurity concentration, by XRD for phase identification and SEM analysis for surface morphology. The critical doping impurities, boron and phosphorous dropped considerably to 18.7 ppm and ND in direct treatment. Thus, the study not only provides an alternative way for recovering pure silicon without the use of harmful chemicals such as HF, but it also recommends a 6 M nitric acid leaching treatment before the etching procedure to lower the concentration of metallic impurities. The results are based on treatments with commercial grade chemicals which ensures the scalability of the process at commercial batch. The profit analysis of the recoverable metals was carried out and estimated to be nearly $19 for an 18 kg c-Si module.

Improving the quality of metallurgical-grade silicon by acid leaching

This work deals with the problem of hydrometallurgical refining of metallurgical-grade silicon. Samples of metallurgical-grade silicon after oxidative refining from JSC Silicon, RUSAL (Shelekhov, Irkutsk Oblast, Russia) were subjected to X-ray fluorescence and electron microprobe analysis. The conducted elemental analysis determined their following composition, wt%: Al – 0.53, Fe – 0.6094, Ti – 0.0491, Ca – 0.0628, V – 0.0066, Cr – 0.002, Mn – 0.014, Cu – 0.003, P – 0.010, Ba – 0.007, Ni – 0.007, and Zn – 0.002. The examined samples were found to comprise the following intermetallic compounds: AlFeSi2 (with an admixture of Ca), FeSi2 (with an admixture of Al), and FeSi2Ti (with an admixture of Zr). In order to purify silicon from impurities, 10% H2SO2, HCl, HNO3, as well as 4% HF in different ratios were used as solvents. The feasibility of interactions between the intermetallic compounds and the selected solvents was assessed by calculating changes in the Gibbs energy, which had negative values. Experiments on impurity leaching were carried out using silicon samples with a particle size of –200 µm under constant stirring with a magnetic stirrer under the temperature of 600С, the liquid-to-solid ratio of 5:1, and the leaching duration of 60 min. The highest degree of silicon purification (86.85%) was achieved under leaching with a mixture of sulfuric and hydrofluoric acids in a ratio of 1:1. The use of a mixture of sulfuric and hydrochloric acids at a ratio of 1:3 resulted in the silicon purification of 41.48%. Thus, optimal solvents allowing the maximum purification of silicon from impurities were determined.

Structure and composition of a composite of porous silicon with deposited copper

Porous silicon is a promising nanomaterial for optoelectronics and sensorics, as it has a large specific surface area and is photoluminescent under visible light. The deposition of copper particles on the surface of porous silicon will greatly expand the range of applications of the resulting nanocomposites. Copper was chosen due to its low electrical resistivity and high resistance to electromigration compared to other metals. The purpose of this research was to study changes in the structure and composition of porous silicon after the chemical deposition of copper. Porous silicon was obtained by the anodisation of monocrystalline silicon wafers KEF (100) (electronic-grade phosphorus-doped silicon) with an electrical resistivity of 0.2 Ohm·cm. An HF solution in isopropyl alcohol with the addition of H2O2 solution was used to etch the silicon wafers. The porosity of the samples was about 70 %. The porous silicon samples were immersed in copper sulphate solution (CuSO4·5H2O) for 7 days. We used scanning electron microscopy, IR spectroscopy, and ultrasoft X-ray emission spectroscopy to obtain data on the morphology and composition of the initial sample and the sample with deposited copper. The chemical deposition of copper on porous silicon showed a significant distortion of the pore shape as well as the formation of large cavities inside the porous layer. However, in the lower part the pore morphology remained the same as in the original sample. It was found that the chemical deposition of copper on porous silicon leads to copper penetrating into the porous layer, the formation of a composite structure, and it prevents the oxidation of the porous layer during storage. Thus, it was demonstrated that the chemical deposition of copper on a porous silicon surface leads to visible changes in the surface morphology and composition. Therefore, it should have a significant impact on the catalytic, electrical, and optical properties of the material.

Nanoscale paraffin layer fabricated using spin coating technique for on-demand removable passivation

Passivation is an essential process in the research and application of reactive and air-sensitive materials, and there has been an increasing demand to develop materials for stable but readily removable temporary passivation layers. Paraffin coating has been suggested as a possible candidate for such applications, which, however, further requires the demonstration of thin paraffin coating with complete surface coverage as well as effective depassivation performance. In this study, we demonstrate on-demand removable passivation using nanoscale paraffin layers fabricated using a spin-coating technique. Based on the Emslie Bonner and Peck's and Mark-Houwink-Sakurada (MHS) equations, eicosane and hexane were selected as the solute and solvent, respectively, to ensure low viscosity for the fabrication of nanoscale paraffin layers, facilitating depassivation process under a vacuum. Optimizing the solution concentration and spin speed generates nanoscale paraffin layers with complete surface coverage, which is confirmed through optical microscopic images and subsequent image processing using Python. The simple removal of the nanoscale paraffin layer through vacuum treatment allows us to revisit a passivated surface underneath, and subsequent contact resistance and x-ray photoelectron spectroscopy measurements evince the suppressed surface oxidation of paraffin-coated silicon samples. These results further attest to the applicability of paraffin coating as an on-demand removable passivation technique.

Silicon surface characteristics in vibration-assisted machining process via molecular dynamics

This study investigates the impacts of vibration amplitude, vibration frequency, and sliding velocity on the characteristics of the machined silicon substrate. The results show that increasing the vibration amplitude increases atomic strain, stress, and kinetic energy distributions while decreasing subsurface damage thickness, potential energy distribution, and especially surface roughness. The surface roughness values are 7.5 Å, 6.4 Å, 6.9 Å, and 6.0 Å corresponding to vibration amplitude of 15 Å, 20 Å, 25 Å, and 30 Å. Moreover, increasing the vibration frequency results in increased atomic strain, stress, and kinetic energy levels. The surface roughness values are 7.1 Å, 7.1 Å, 6.5 Å, 6.4 Å, and 6.0 Å corresponding to the vibration frequencies of 16.7 GHz, 33.3 GHz, 50 GHz, 66.7 GHz, 100 GHz, and 200 GHz. Furthermore, increasing the sliding velocity lowers the surface quality of the silicon sample. The surface roughness values of the silicon substrate are 6.5 Å, 6.7 Å, 6.9 Å, 6.9 Å, and 7.1 Å corresponding to 50 m/s, 100 m/s, 150 m/s, 200 m/s, and 250 m/s. Improving the vibration amplitude and frequency while decreasing the sliding velocity improves surface quality by increasing the collision between the diamond tips and the substrate. Remarkably, the vibration movement of the diamond tips could leave wave marks on the substrate surface. In general, the optimal parameters that generate a good surface are 30 Å, 200 GHz, and 50 m/s.

Study of surface damage in silicon by irradiation with focused rubidium ions using a cold-atom ion source

Cold-atom ion sources have been developed and commercialized as alternative sources for focused ion beams (FIBs). So far, applications and related research have not been widely reported. In this paper, a prototype rubidium FIB is used to study the irradiation damage of 8.5 keV beam energy Rb+ ions on silicon to examine the suitability of rubidium for nanomachining applications. Transmission electron microscopy combined with energy dispersive x-ray spectroscopy is applied to silicon samples irradiated by different doses of rubidium ions. The experimental results show a duplex damage layer consisting of an outer layer of oxidation without Rb and an inner layer containing Rb mostly at the interface to the underlying Si substrate. The steady-state damage layer is measured to be 23.2(±0.3) nm thick with a rubidium staining level of 7(±1) atomic percentage.