Surface Of Single Crystalline Silicon Research Articles

Sheet conductance of laser-doped layers using a Gaussian laser beam: an effective depth approximation

Laser doping of silicon with pulsed and scanned laser beams is now well-established to obtain defect-free, doping profile tailored, and locally selectively doped regions with a high spatial resolution. Picking the correct laser parameters (pulse power, pulse shape, and scanning speed) impacts the depth and uniformity of the melted region geometry. This work performs laser doping on the surface of single crystalline silicon, using a pulsed and scanned laser profile with a Gaussian intensity distribution. A deposited boron oxide precursor layer serves as a doping source. Increasing the local inter-pulse distance xirr\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$x_\ ext {irr}$$\\end{document} between subsequent pulses causes a quadratic decrease of the sheet conductance Gsh\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$G_\ ext {sh}$$\\end{document} of the doped surface layer. Here, we present a simple geometric model that explains all experimental findings. The quadratic dependence stems from the approximately parabolic shape of the individual melted regions directly after the laser beam has hit the Si surface. The sheet resistance depends critically on the intersection depth dch\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d_\ ext {ch}$$\\end{document} and the distance xirr\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$x_\ ext {irr}$$\\end{document} of overlap between two subsequent, neighboring pulses. The intersection depth dch\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d_\ ext {ch}$$\\end{document} quadratically depends on the pulse distance xirr\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$x_\ ext {irr}$$\\end{document} and therefore also on the scanning speed vscan\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$v_\ ext {scan}$$\\end{document} of the laser. Finally, we present a simple model that reduces the complicated three dimensional, laterally inhomogeneous doping profile to an effective two-dimensional, homogeneously doped layer which varies its thickness with the scanning speed.

THE EFFECT OF PLASMA SURFACE TREATMENT ON THE STRUCTURE OF THE LEAD SULFIDE FILM

In this work, the effect of the substrate surface on the formation of structured lead sulfide films is studied. For this purpose, the surface of single-crystalline silicon (100) was subjected to plasma treatment in a glow discharge in an argon atmosphere, at a working pressure of 1 Pa and a potential difference across the electrodes of 2 kV. Lead sulfide films were obtained on treated and untreated single-crystalline silicon surfaces by chemical deposition from an aqueous solution of lead nitrate, thiourea and sodium hydroxide at a temperature of 70°C for 30 minutes. The surface morphology, elemental composition, and crystal structure were studied by scanning electron microscopy, energy dispersive analysis, and X-ray diffraction, respectively. As a result, the films deposited on pretreated substrates have a distinctly different surface structure compared to films deposited on untreated substrates. Under the same synthesis conditions, the growth of crystals on the treated surface occurred predominantly along certain lines and were grouped into individual particles, while on the untreated surface a continuous film was formed. Thus, through plasma treatment, crystal growth can be controlled to create nanostructures.

Chemical Vapor Deposition of Textured Diamond Film through Pre-Seeding by Diamond Nano-Sheets

Diamond films prepared by chemical vapor deposition will exhibit different surface morphologies, which are determined by the texture and the structural perfection of the deposited diamond. In general, its surface morphology can be controlled by adjusting the deposition conditions. In the present work, <110> textured diamond film was deposited on single crystalline silicon through pre-seeding by diamond nanosheets, rather than controlling the deposition conditions. The employed diamond nano-sheets were prepared by cleavage along a plane, exhibiting good crystallinity. Before chemical vapor deposition, the as-prepared diamond nano-sheets were pre-seeded on the surface of single crystalline silicon as nucleation sites for diamond growth. SEM and XRD results show that the prepared diamond films have a <110> texture. FIB observation reveals that diamonds homogeneously grow on the pre-seeded diamond nano-sheets during chemical vapor deposition, achieving the diamond film with <110> texture. Our work provides a new strategy to prepare <110> textured diamond film.

Approximately 30 nm Nanogroove Formation on Single Crystalline Silicon Surface under Pulsed Nanosecond Laser Irradiation.

Nanogrooves with a minimum feature size down to 30 nm (λ/26) can be formed directly on silicon surface by irradiation from two orthogonal polarized 1064 nm/10 ns fiber laser beams. The creation of such small nanogrooves is attributed to surface thermal stress during resolidification and supercooling with the double laser beams' irradiation. By varying the pulse number and laser fluence, the feature size of narrow grooves on silicon surface can be tuned. The experimental results and numerical calculation of surface thermal behaviors indicated that the high repetition rate of the nanosecond laser leads to the incubation effect and different silicon optical and thermal properties during laser irradiation. Resolution on this scale should be attractive in nanolithography, particularly considering that this method is available in far field and in ambient air.

Light Sensors Based on Silicon Nanowires

The article deals with the synthesis of silicon nanowires by the method of metal-assisted chemical etching (MACE). The purpose of this work is to use in light sensors silicon nanowires that synthesized by the MACE. To achieve this goal, it was necessary to synthesize silicon nanowires by the MACE and to study their structural features, to obtain diode structures based on silicon nanowires and to study their sensitivity to visible radiation, to establish the influence of technological parameters of the MSHT process on the sensitivity of photo sensors and sensors. Today, nanostructures are obtained by the method of reactive ion etching, electrochemical etching and plasma implantation. However, most of these methods require sophisticated process equipment. Metal-assisted chemical etching (MACE) method is very promising for nanostructures creation. Two-stage MACE was used to make the samples. In the first stage, silver nanoparticles were deposited on the surface of single crystalline silicon. In the second stage, the samples were etched in a solution of water, hydrogen peroxide and hydrofluoric acid and, as a consequence, a structured surface was obtained. It should be noted that the samples were treated at different times of each of the stages of MACE. Based on the obtained samples, diode light sensors with different photoelectric parameters were synthesized. For the sensors obtained, the sensitivity was calculated in the photodiode and photogenerator modes, and the volt-ampere, luxury-ampere characteristics and dependences of the current density on the illumination density were constructed. structured silicon has a mesh-like appearance, where the dark regions are gaps (pores) and the light ones are silicon (pore walls, nanowires). First, compare the samples with different deposition times. It is seen that as the deposition time of the particles increases from 10 to 40 s, a more developed silicon surface is formed. Also, with the duration of deposition 40s on the silicon surface there are needle-like formations, which according to the results in the work are silver dendrites. All the above characteristics were analyzed for the effect of the deposition time of silver particles t1 and etching time t2 on them. Studies have shown that the optimum technological conditions of metal assisted chemical etching of silicon for using in light sensors are the following conditions: the deposition time of silver particles 40c, etching time 30 min, the content of hydrogen peroxide in the second solution of 0.8 ml. This mode of synthesis of the structuring of silicon substrates provides maximum photosensitivity ratios both in the photodiode (1.53 mA / lmV) and in the photogenerator (304 mA / W) modes. The influence of the concentration of H2O2 used in the second stage is crucial only for the photocurrent, which is not critical, and the influence of the AgNO3 concentration in the first stage of MACE does not have a significant effect on the parameters.

Epitaxial Bottom-up Growth of Silicon Nanowires on Oxidized Silicon by Alloy-Catalyzed Gas-Phase Synthesis.

High-yield epitaxial bottom-up growth of silicon nanowires is still challenging but desirable for various applications such as antireflective coatings, solar cells, and high-aspect-ratio scanning probes. Hence, pristine single-crystalline silicon surfaces are, in principle, required as a growth substrate, but reoxidation occurring prior to nanowire growth obstructs epitaxial growth significantly. Here, we present an approach that relies on Al/Au alloy catalysts for gas-phase silicon nanowire synthesis, allowing intrinsically an in situ removal of a native silicon-oxide layer during the initial growth stages. This approach yields reliable and superior epitaxial growth of silicon nanowires on single-crystalline silicon substrates.

Hydrophobic nanostructures fabricated by ferric nitrate etching method on single crystalline silicon surface

To improve the hydrophobicity of the surfaces of single crystalline silicon (sc-Si) wafers, hierarchical structures were fabricated on the surfaces of sc-Si wafers by using Fe(NO3)3/HF mixed solution as an etchant. Scanning electron microscope, atomic force microscope and water contact angle were used to characterize the etching of sc-Si wafers. It was found that after the etching process the surface micro/nano-structures having hemispherical etched pits with needle-like folds can be formed and the surface of sc-Si wafers possess hydrophobicity. The concentration of Fe(NO3)3, etching temperature and etching time have important impacts on surface morphology and surface hydrophobicity of the sc-Si. Results showed that the surface water contact angle of etched sc-Si wafers decreased with the increase of the concentration of Fe(NO3)3. The surface water contact angle of the sc-Si wafer treated with 0.2 M of Fe(NO3)3 is highest (124.37°) and increased by 145.89% compared to that of control sc-Si wafers due to the smallest surface roughness and the most smooth surface. Surface wettability of sc-Si wafers varied from hydrophobic to hydrophilic as the etching temperature increasing from 30 °C to 70 °C. When the etching temperature was 30 °C and 70 °C, the surface water contact angle of sc-Si wafer was 142.32° and 13.86°, respectively. With the increase of the etching time, rough grooves formed on the surface of sc-Si wafers and the roughness changed larger. Hydrophobic surfaces with a water contact angle up to 144.50° were obtained at etching time of 30 min.

Silicon and germanium nanostructures formed by spark discharge plasma

Formation of semiconductor nanostructures on the surface of single crystalline silicon and germanium wafers by spark discharge plasma in air was investigated. The prepared nanostructures were analyzed by means of the scanning and transmission electron microscopy and optical spectroscopy of the photoluminescence and Raman scattering. The formed nanostructures exhibit a fractal-like morphology with interconnected nanocrystals of 2-200 nm sizes that is explained by repeated processes of spark ablation and subsequent condensation. While the size and morphology of the nanostructure depend on power sources of the spark discharge, short interaction times of spark discharge plasma and target determine a relatively low efficiency of the chemical oxidation of germanium and silicon, as well as low ionic temperatures of the plasma.

Nanomanufacturing of silicon surface with a single atomic layer precision via mechanochemical reactions

Topographic nanomanufacturing with a depth precision down to atomic dimension is of importance for advancement of nanoelectronics with new functionalities. Here we demonstrate a mask-less and chemical-free nanolithography process for regio-specific removal of atomic layers on a single crystalline silicon surface via shear-induced mechanochemical reactions. Since chemical reactions involve only the topmost atomic layer exposed at the interface, the removal of a single atomic layer is possible and the crystalline lattice beneath the processed area remains intact without subsurface structural damages. Molecular dynamics simulations depict the atom-by-atom removal process, where the first atomic layer is removed preferentially through the formation and dissociation of interfacial bridge bonds. Based on the parametric thresholds needed for single atomic layer removal, the critical energy barrier for water-assisted mechanochemical dissociation of Si–Si bonds was determined. The mechanochemical nanolithography method demonstrated here could be extended to nanofabrication of other crystalline materials.

The influence of water–organic solvent composition on the morphology and luminescent properties of CdS nanoparticles obtained by chemical precipitation

Cadmium sulfide (CdS) nanoparticles have been obtained by chemical precipitation onto the surface of single-crystalline silicon from an aqueous solution of ammonia, cadmium chloride (CdCl2), and thiourea, as well as from water–DMSO and water–DMF mixtures with the same concentrations of the reagents. According to data of atomic force microscopy, the samples obtained from the aqueous solution consist of individual nanoparticles and agglomerates thereof with sizes of no larger than 1 µm. Materials obtained from the water–organic mixtures are distinguished by the aggregation of CdS nanoparticles into threadlike chains. The length of the formed curved chains and the size of CdS nanoparticles composing them depend on the nature and amount of an organic component of a mixture. Atomic force microscopy, transmission electron microscopy, and photoluminescence spectroscopy data have shown that the average size of CdS nanoparticles is 2–2.5 nm depending on solvent composition.

Nanostructured Silicon Photocathodes for Solar Water Splitting Patterned by the Self-Assembly of Lamellar Block Copolymers.

We studied a type of nanostructured silicon photocathode for solar water splitting, where one-dimensionally periodic lamellar nanopatterns derived from the self-assembly of symmetric poly(styrene-block-methyl methacrylate) block copolymers were incorporated on the surface of single-crystalline silicon in configurations with and without a buried metallurgical junction. The resulting nanostructured silicon photocathodes with the characteristic lamellar morphology provided suppressed front-surface reflection and increased surface area, which collectively contributed to the enhanced photocatalytic performance in the hydrogen evolution reaction. The augmented light absorption in the nanostructured silicon directly translated to the increase of the saturation current density, while the onset potential decreased with the etching depth because of the increased levels of surface recombination. The pp(+)-silicon photocathodes, compared to the n(+)pp(+)-silicon with a buried solid-state junction, exhibited a more pronounced shift of the current density-potential curves upon the introduction of the nanostructured surface owing to the corresponding increase in the liquid/silicon junction area. Systematic studies on the morphology, optical properties, and photoelectrochemical characteristics of nanostructured silicon photocathodes, in conjunction with optical modeling based on the finite-difference time-domain method, provide quantitative description and optimal design rules of lamellar-patterned silicon photocathodes for solar water splitting.

Experimental Study of Combined Effects of Gamma and Laser Radiations on the Properties of Silicate Glass Materials

Effect of 60Co γ-ray radiation at room temperature up to a dose of 5∙107 Gy on the parameters of laser-generated plasma ions at the surface of single crystalline silicon and multicomponent silicate glass targets is investigated using time-of-flight mass spectrometer based on an electrostatic energy analyzer. The main impact of the radiation is observed in the charge state of the plasma ions: for small energy ions the charge increases with increasing the radiation dose, whereas the increase in the radiation dose results in the decrease of the charge of high-energy ions. The maximum energy of the ions also decreases with increasing the radiation dose. Effect of point defects created by metal atom inclusions on the absorption properties of silicate glasses is also studied. The defects decrease the resistance of the glasses to optical damage as they become centers of intense light absorption.

Tribology of Si/SiO2 in humid air: transition from severe chemical wear to wearless behavior at nanoscale.

Wear at sliding interfaces of silicon is a main cause for material loss in nanomanufacturing and device failure in microelectromechanical system (MEMS) applications. However, a comprehensive understanding of the nanoscale wear mechanisms of silicon in ambient conditions is still lacking. Here, we report the chemical wear of single crystalline silicon, a material used for micro/nanoscale devices, in humid air under the contact pressure lower than the material hardness. A transmission electron microscopy (TEM) analysis of the wear track confirmed that the wear of silicon in humid conditions originates from surface reactions without significant subsurface damages such as plastic deformation or fracture. When rubbed with a SiO2 ball, the single crystalline silicon surface exhibited transitions from severe wear in intermediate humidity to nearly wearless states at two opposite extremes: (a) low humidity and high sliding speed conditions and (b) high humidity and low speed conditions. These transitions suggested that at the sliding interfaces of Si/SiO2 at least two different tribochemical reactions play important roles. One would be the formation of a strong "hydrogen bonding bridge" between hydroxyl groups of two sliding interfaces and the other the removal of hydroxyl groups from the SiO2 surface. The experimental data indicated that the dominance of each reaction varies with the ambient humidity and sliding speed.

REDUCTION OF REFLECTION LOSSES IN SOLAR CELL BY USING TIAL2 AND ZR ANTI REFLECTIVE COATING

Direct energy conversion from sunlight to electricity is obtained through solar cells. The Efficiency of solar cells is about 23.89% in the laboratory and 13.76%. More than 30% of incident light is reflected back from the surface of single crystalline Silicon (Si) solar cells because of the high refractive index of Silicon material. The initial objective of this project is to minimize the reflection losses in solar cells using an Anti-Reflection coating (ARC). In solar cell applications, a single layer thin film Anti-Reflective coating is often used. But such a Single Layer Anti-Reflective coating (SLARC) and Double layer Anti-Reflective coating reduces reflectivity only in a limited range. Triple Layer Anti-Reflective coatings (TLARC) are so widely utilized to improve conversion efficiencies and current density of silicon solar cells. Such Triple layer anti reflective coating can eliminate the need for a mechanical tracking device for proper optical alignment of the solar cell with respect to incident sunlight.

Effect of RF Negative Bias on the Structure and Performance of Diamond-Like Carbon Films in ECR Plasma

Diamond-like carbon films (DLC) were deposited on single crystalline silicon surface under different RF negative bias in microwave electron cyclotron resonance (ECR) plasma source. The chemical structure and morphology were characterized by Fourier transformation infrared spectroscopy (FTIR) and atomic force microscopy (AFM). The friction coefficient of films was measured to examine the film property later. The results show that the smooth and compact deposited films were typical hydrogenated diamond-like carbon with CHn stretching vibration in 2800-3000cm-1. It is noticed that with the increase of RF bias on the substrate the peak intensity for C-H stretching vibration in spectrum between 2800cm-1~3000cm-1increased at the beginning and then decreased, which caused the friction coefficient of the film being smaller and then larger in reverse. In 50W RF biased power one can obtain the maximum-CHn peak intensity and the minimum friction coefficient.

Wavy microstructures formed at the SiO2/Si interface under the action of high-power ion-beam pulses

The formation of wavy microstructures under the action of a nanosecond pulsed high-power ion beam on the surface of single-crystalline silicon covered with intrinsic oxide layers of various thickness has been studied. Morphological features of the observed structures depend on the oxide layer thickness and ion beam current density. Possible mechanisms of formation of these microstructures are considered.

Graphene on Si(111)7×7

We demonstrate that it is possible to mechanically exfoliate graphene under ultrahigh vacuum conditions on the atomically well defined surface of single crystalline silicon. The flakes are several hundred nanometers in lateral size and their optical contrast is very faint, in agreement with calculated data. Single-layer graphene is investigated by Raman mapping. The graphene and 2D peaks are shifted and narrowed compared to undoped graphene. With spatially resolved Kelvin probe measurements we show that this is due to p-type doping with hole densities of nh ≃ 6 × 1012 cm−2. The invacuo preparation technique presented here should open up new possibilities to influence the properties of graphene by introducing adsorbates in a controlled way.

Formation of surface structures on single-crystalline silicon under the action of nanosecond high-power ion beam pulses

We have studied the formation of surface structures on single-crystalline silicon surface under the action of a nanosecond pulsed high-power proton-carbon ion beam. Morphological features of the structures that appear as a result of this processing are described and possible mechanisms of their formation are considered.

Fabrication and Morphology of KOH Etching Single Crystalline Silicon Solar Cells

Anisotropic etching process by potassium hydroxide (KOH) and isopropyl alcohol (IPA) mixed solution in the [100] orientation silicon wafer was studied experimentally. The effect parameters of KOH concentration, IPA concentration, reaction time and temperature for wafer surface morphology were analyzed by scanning electron microscope. The results show that: a uniform, high density and good pyramid shaped single crystalline silicon surface can be obtained at 3% KOH solution buffered with 8% IPA at 80°C for 30min. By comparing single crystalline silicon micro-surface with NaOH and IPA mixed solution system of industrial fabrication, the pyramid structure is more regular and uniform by using KOH and IPA mixed solution system, which is expected to obtain better optical properties.

RIE 공정 조건에 의한 피라미드 구조의 블랙 실리콘 형성

In this study, pyramid structured black silicon process was developed in order to overcome disadvantages of using wet etching to texture the surface of single crystalline silicon and using grass/needle-like black silicon structure. In order to form the pyramidal black silicon structure on the silicon surface, the RIE system was modified to equip with metal-mesh on the top of head shower. The process conditions were : <TEX>$SF_6/O_2$</TEX> gas flow 15/15 sccm, RF power of 200 W, pressure at 50 mTorr ~ 200 mTorr, and temperature at <TEX>$5^{\circ}C$</TEX>. The pressure did not affect the pyramid structure significantly. Increasing processing time increased the size of the pyramid, however, the size remained constant at 1 <TEX>${\mu}M$</TEX> ~ 2 <TEX>${\mu}M$</TEX> between 15 minutes ~ 20 minutes of processing. Pyramid structure of 1 <TEX>${\mu}M$</TEX> in size showed to have the lowest reflectivity of 7 % ~ 10 %. Also, the pyramid structure black silicon is more appropriate than the grass/needle-like black silicon when creating solar cells.