Melting Point Of Silicon Research Articles

Temperature and hydrogen diffusion length in hydrogenated amorphous silicon films on glass while scanning with a continuous wave laser at 532 nm wavelength

Rapid thermal annealing by, e.g., laser scanning of hydrogenated amorphous silicon (a-Si:H) films is of interest for device improvement and for development of new device structures for solar cell and large area display application. For well controlled annealing of such multilayers, precise knowledge of temperature and/or hydrogen diffusion length in the heated material is required but unavailable so far. In this study, we explore the use of deuterium (D) and hydrogen (H) interdiffusion during laser scanning (employing a continuous wave laser at 532 nm wavelength) to characterize both quantities. The evaluation of temperature from hydrogen diffusion data requires knowledge of the high temperature (T > 500 °C) deuterium-hydrogen (D-H) interdiffusion Arrhenius parameters for which, however, no experimental data exist. Using data based on recent model considerations, we find for laser scanning of single films on glass substrates a broad scale agreement with experimental temperature data obtained by measuring the silicon melting point and with calculated data using a physical model as well as published work. Since D-H interdiffusion measures hydrogen diffusion length and temperature within the silicon films by a memory effect, the method is capable of determining both quantities precisely also in multilayer structures, as is demonstrated for films underneath metal contacts. Several applications are discussed. Employing literature data of laser-induced temperature rise, laser scanning is used to measure the H diffusion coefficient at T > 500 °C in a-Si:H. The model-based high temperature hydrogen diffusion parameters are confirmed with important implications for the understanding of hydrogen diffusion in the amorphous silicon material.

Investigating the effects of vacancies on self-diffusion in silicon clusters using classical molecular dynamics.

Due to recent advances in the field of microelectronics, the growth in microelectronics applications, and the exponentially increasing demand for microelectronic devices in the power sector, it is important to study the behavior of silicon at the nanoscale, given that nanoclusters of silicon could be used to design a new kind of lithium-ion batteries with strongly enhanced performance. Here, molecular dynamics was employed to calculate the self-diffusion coefficients of silicon clusters at room temperature and at a temperature approaching the melting point of silicon, complementing experimental efforts in this field. Silicon clusters of the same spherical geometry and size but with different vacancy fractions were studied using molecular dynamics using the Tersoff potential in order to estimate phase changes and self-diffusion coefficients. At 300K, the self-diffusion coefficient was found to vary non-monotonically: the self-diffusion coefficient at a vacancy fraction of 7.5% is half than the vacancy at a fraction of 0%, while the self-diffusion coefficient at a vacancy fraction of 20% is two orders of magnitude larger than that at a vacancy fraction of 0%. However, there is only a marginal monotonic increase in the self-diffusion coefficient values with vacancy fraction at 2000K. The results of this investigation of vacancy-mediated self-diffusion could aid attempts to improve diffusion control, which is crucial to nanocluster applications in various devices, and the results also provide insight into how the temperature, energy, pressure, and phase changes of the silicon clusters depend on vacancy fraction. This may ultimately allow the design and selection of materials for thermoelectric and optoelectronic devices and thermal transducers to be optimized. Our results also indicated that the findings we obtained for the clusters are independent of the particular random vacancy distribution considered and the heating rate applied to the clusters. Graphical Abstract Silicon nanoparticles (SNP) are among the best options to choose from for the design of devices for renewable energies; SNP based material performance can be effectively tailored by controling the vacancy, temperature and other properties of the SNP.

Addressing the discrepancy of finding the equilibrium melting point of silicon using molecular dynamics simulations.

We performed molecular dynamics simulations to study the equilibrium melting point of silicon using (i) the solid-liquid coexistence method and (ii) the Gibbs free energy technique, and compared our novel results with the previously published results obtained from the Monte Carlo (MC) void-nucleated melting method based on the Tersoff-ARK interatomic potential (Agrawal et al. Phys. Rev. B72, 125206. (doi:10.1103/PhysRevB.72.125206)). Considerable discrepancy was observed (approx. 20%) between the former two methods and the MC void-nucleated melting result, leading us to question the applicability of the empirical MC void-nucleated melting method to study a wide range of atomic and molecular systems. A wider impact of the study is that it highlights the bottleneck of the Tersoff-ARK potential in correctly estimating the melting point of silicon.

On-the-fly dopant redistribution in a silicon nanowire p–n junction

Dopant redistribution in a silicon nanowire (SiNW) p–n junction is found to occur owing to self-heating effects. A SiNW is doped to form back-to-back diodes and is thermally isolated by an oxide layer on its bottom side and by air on the other sides. When a high level of current flows, the inner body temperature is found to increase enough to cause dopant diffusion and even to reach the silicon melting point due to Joule heating. This experimentally observed electrothermal behavior is also validated through numerical simulation. The conductivity change is dependent on the total power density and the change becomes permanent once the device suffers self-heating beyond a threshold point. Finally, the dopant redistribution is directly visualized using scanning capacitance microscopy for the first time.

Resonant Nonplasmonic Nanoparticles for Efficient Temperature-Feedback Optical Heating.

We propose a novel photothermal approach based on resonant dielectric nanoparticles, which possess imaginary part of permittivity significantly smaller as compared to metal ones. We show both experimentally and theoretically that a spherical silicon nanoparticle with a magnetic quadrupolar Mie resonance converts light to heat up to 4 times more effectively than similar spherical gold nanoparticle at the same heating conditions. We observe photoinduced temperature raise up to 900 K with the silicon nanoparticle on a glass substrate at moderate intensities (<2 mW/μm2) and typical laser wavelength (633 nm). The advantage of using crystalline silicon is the simplicity of local temperature control by means of Raman spectroscopy working in a broad range of temperatures, that is, up to the melting point of silicon (1690 K) with submicrometer spatial resolution. Our CMOS-compatible heater-thermometer nanoplatform paves the way to novel nonplasmonic photothermal applications, extending the temperature range and simplifying the thermoimaging procedure.

Experimental study of burnout of microwave bipolar transistors under action of a series of electric pulses

Burnout of silicon transistors under the action of a periodic train of electric pulses is experimentally studied. A numerical model and a more physically demonstrative analytical model of the pulse-to-pulse heat accumulation are in qualitative and, to a certain extent, quantitative agreement with the measured results. It is demonstrated that catastrophic failure takes place at a melting point of silicon but additional heat is needed for melting of low-temperature eutectics.

High-Temperature (1200–1400°C) Dry Oxidation of 3C-SiC on Silicon

In a novel approach, high temperatures (1200–1400°C) were used to oxidize cubic silicon carbide (3C-SiC) grown on silicon substrate. High-temperature oxidation does not significantly affect 3C-SiC doping concentration, 3C-SiC structural composition, or the final morphology of the SiO2 layer, which remains unaffected even at 1400°C (the melting point of silicon is 1414°C). Metal-oxide-semiconductor capacitors (MOS-C) and lateral channel metal-oxide-semiconductor field-effect-transistors (MOSFET) were fabricated by use of the high-temperature oxidation process to study 3C-SiC/SiO2 interfaces. Unlike 4H-SiC MOSFET, there is no extra benefit of increasing the oxidation temperature from 1200°C to 1400°C. All the MOSFET resulted in a maximum field-effect mobility of approximately 70 cm2/V s.

3C-SiC Crystal on Sapphire by Solution Growth Method

We realized the growth of 3C-SiC crystal on sapphire by solution growth method. The carbon deposition on a sapphire substrate before growth is the key point for this technology. This carbon layer plays a role to protect the dissolution of sapphire by Si solvent. Single crystal of 3C-SiC was grown on the whole surface of the sapphire substrate. Surprisingly, the 3C-SiC layer did not directly grown on the sapphire substrate. The single crystal 3C-SiC layer formed by the reaction between the deposited carbon and the Si wafer that is a solvent material below the melting point of silicon during heating process before the growth. The 3C-SiC grew on the 3C-SiC layer. In this process, the deposited carbon play another important role.

Density-functional-theory-based calculations of formation energy and concentration of the silicon monovacancy

By using first-principles calculations, we study the formation energy and concentration of the silicon monovacancy. We use large-scale supercells containing up to 1728 atomic sites and confirm the convergence of calculational results with respect to the cell size. The formation energy is calculated to be 3.46 eV, and the vacancy concentration at the silicon melting point is estimated to be 7.4 × 1016 cm−3. These values are consistent with experimental results. We find that the vibrational effect significantly increases the vacancy concentration about 104 times.

On the mechanism of ion desorption in the process of laser desorption/ionization from silicon surfaces

The mechanism of ion desorption in the process of laser desorption/ionization from silicon surfaces is studied using pyridine and N,N-dimethyl-1-phenylethylamine as examples. Based on the experimental and theoretical results, dependences of ion signal on the surface temperature are obtained for two different wavelengths of laser radiation, 355 nm and 532 nm. The theoretical part of the work includes numerical calculations of surface temperatures of amorphous silicon using the SLIM software package and quantum-chemical calculations of binding energy between the ions and silicon surface using the Hartree-Fock method and Firefly software package. It is demonstrated that the ions are desorbed via a thermal mechanism at temperatures much lower than the melting point of amorphous silicon.

Combustion characteristics of molybdenum–silicon mixtures

Molybdenum disilicide was produced from elemental powder compacts of molybdenum and silicon by self-propagating high-temperature synthesis. The effects of the reactant ratio, particle size of silicon, and density of the compact were investigated in a high-pressure microreactor. In order to get the relationships among them, the atomic ratio of silicon to molybdenum (Si/Mo) was changed from the values of 1.0 to 2.6 with steps of 0.2. Stable combustion was observed for values of atomic ratio of silicon to molybdenum of 1.8, 2.0, and 2.2. The SHS-produced material consisted of uniform and single-phased molybdenum disilicide (MoSi2) for the atomic ratio of silicon to molybdenum of 2.0. In the meantime unstable combustion such as oscillatory and spinning combustion was detected for values of atomic ratio of silicon to molybdenum beyond the limits of stable combustion. The SHS-produced material under unstable combustion includes impurities of Mo5Si3, unreacted Mo and Si resulting from the layered structure which gives a lower degree of reaction and poor electrical properties of MoSi2 heating element. A significant amount of unreacted molybdenum (≈17%) was found for the atomic ratio of silicon to molybdenum of 1.0. This may result from the spinning combustion as well as from the low combustion temperature below the melting point of silicon (≈1414°C). The value of criterion α suggested by Shkadinskii et al. to differentiate stable combustion from unstable one, is found to be 0.74 for the production of molybdenum disilicide by self-propagating high-temperature synthesis. Stable combustion was observed for α≥0.74 to give uniform products while unstable combustion was detected for α<0.74 to result in non-uniform and multi-phased products. This critical value should be useful for the industrial production of uniform molybdenum disilicide by self-propagating high-temperature synthesis.

Bulk Silicon Crystals with the High Boron Content, Si1–xBx: Two Semiconductors Form an Unusual Metal

Silicon is a key technological material, and its controlled doping is one of the simple and effective ways which are applied for creation of new advanced materials with tunable optoelectronic properties. Boron was known to be a dopant that can dramatically change the properties of silicon. However, a limited solubility of boron atoms in silicon matrix strongly restricted creation of bulk diamond-type structured Si–B alloys with the high boron content exceeding 0.5–1 at. %. In this work we show that bulk Si1–xBx alloys with a rather high boron content (e.g., 2.4 at. %) may be fabricated by alloying of boron and silicon at high temperatures above the melting point of silicon and high pressure. We extensively investigated the electronic transport and optical properties of these alloys using several techniques, including electrical resistivity, Hall effect, magnetoresistance, Raman, IR and optical spectroscopy, and X-ray diffraction. We found that Si1–xBx solid solutions are metals that possess very unusual o...

Improvement of the growth stability for large diameter Si-float zone crystals by controlling the gas flow

For the growth of large float zone (FZ) silicon crystals, currently limited to 200 mm diameter, a high process stability is necessary. A major drawback are arc discharges at the inductor, when the increasing diameter of the growing crystal requires higher RF voltages. An arc discharge mostly interrupts the dislocation-free growth of the crystal. Increasing the gas pressure or adding some nitrogen to the growth atmosphere increases its electrical strengths. For reduced working frequencies the inductor voltage is lowered, too. However, the usability of these measures is limited. The aim of this work was to investigate another concept to reduce the probability of arcing. Numerical calculations of the convective gas flow in a typical FZ puller revealed a high gas temperature, being close to the silicon melting point temperature in the vicinity of the melt surface. The gas temperature near the inductor and especially its influence on the risk of arcing, were investigated. Several experiments confirm a significantly higher breakdown voltage at lower temperature in comparable conditions by controlling the gas flow. This was performed using a thin quartz plate covering at least the whole lower inductor surface including the main slit where the electric field is strong. Therefore, the temperature will be lowered due to the separation of the hot gas flow from the critical slit region. It could been shown, that the risk of arcing could be noticeable reduced for 6 inch crystals grown under comparable conditions The results will be supported by global numerical simulations showing the flow field and the temperature distribution of the gas. The protection of the critical region by changing the gas flow appears as a new potent measure to prevent arcing and to enable larger crystals.

Night time performance of a storage integrated solar thermophotovoltaic (SISTPV) system

Energy storage at low maintenance cost is one of the key challenges for generating electricity from the solar energy. This paper presents the theoretical analysis (verified by CFD) of the night time performance of a recently proposed conceptual system that integrates thermal storage (via phase change materials) and thermophotovoltaics for power generation. These storage integrated solar thermophotovoltaic (SISTPV) systems are attractive owing to their simple design (no moving parts) and modularity compared to conventional Concentrated Solar Power (CSP) technologies. Importantly, the ability of high temperature operation of these systems allows the use of silicon (melting point of 1680K) as the phase change material (PCM). Silicon’s very high latent heat of fusion of 1800kJ/kg and low cost ($1.70/kg), makes it an ideal heat storage medium enabling for an extremely high storage energy density and low weight modular systems. In this paper, the night time operation of the SISTPV system optimised for steady state is analysed. The results indicate that for any given PCM length, a combination of small taper ratio and large inlet hole-to-absorber area ratio are essential to increase the operation time and the average power produced during the night time. Additionally, the overall results show that there is a trade-off between running time and the average power produced during the night time. Average night time power densities as high as 30W/cm2 are possible if the system is designed with a small PCM length (10cm) to operate just a few hours after sun-set, but running times longer than 72h (3days) are possible for larger lengths (50cm) at the expense of a lower average power density of about 14W/cm2. In both cases the steady state system efficiency has been predicted to be about 30%. This makes SISTPV systems to be a versatile solution that can be adapted for operation in a broad range of locations with different climate conditions, even being used off-grid and in space applications.

Interaction modes in Mo/Si diffusion couple at non-isothermal conditions

Non-isothermal siliconizing in Si-clad Mo wires has been studied over a wide range of heating rates Vh and silicon layer thicknesses δSi. At T = 1000–1600°C, the reaction was found to proceed in two stages: by Mo(s) + Si(s) mechanism (stage I) and by Mo(s) + Si(l) mechanism (stage II). For sufficiently thin silicon layers, non-isothermal Mo-Si reaction is single-step and ends up before reaching the melting point of silicon: a decrease in the heating rate is accompanied by marked expansion of a range of Si layer thickness (δSi) within which the Mo-Si reaction accomplishes at stage I. Based on the above data, the Vh-δSi diagram discerning four different siliconizing modes of Mo was plotted. Within a wide range of heating rates and for sufficiently small Mo particles non-isothermal reaction of Mo with Si may proceed by purely solid-state mechanism.

Near-Net Shaping of Silicon for Optical Lens by One-Shot Pressing at Temperature just below Silicon Melting Point and Improvement of Infrared Transmittance by Primary Recrystallization

Silicon is brittle and easily cracks even under a small load. The difficulty in shaping silicon has prevented breakthroughs in the mass production of silicon lenses for terahertz and infrared technology. We developed a novel method of deforming bulk single-crystal silicon into the required shape by one-shot pressing at a temperature just below the melting point of silicon, despite its brittleness and covalent nature, and realized the near-net shaping of the material into the plano-convex shape with the curvature radius R=7.5 mm for a infrared transmission lens. The crystallographic quality of the obtained lens could be improved by primary recrystallization. The simple method of 'pressing' will enable the mass production of not only silicon lenses but also lenses with a complex shape, such as aspherical lenses, and lens arrays by using dies with desired shape.

The role of physical and chemical properties of Pd nanostructured materials immobilized on inorganic carriers on ion formation in atmospheric pressure laser desorption/ionization mass spectrometry.

Fundamental parameters influencing the ion-producing efficiency of palladium nanostructures (nanoparticles [Pd-NP], nanoflowers, nanofilms) during laser irradiation were studied in this paper. The nanostructures were immobilized on the surface of different solid inorganic carrier materials (porous and mono-crystalline silicon, anodic porous aluminum oxide, glass and polished steel) by using classical galvanic deposition, electroless local deposition and sputtering. It was the goal of this study to investigate the influence of both the nanoparticular layer as well as the carrier material on ion production for selected analyte molecules. Our experiments demonstrated that the dimensions of the synthesized nanostructures, the thickness of the active layers, surface disorders, thermal conductivity and physically or chemically adsorbed water influenced signal intensities of analyte ions during surface-assisted laser desorption/ionization (SALDI) while no effects such as plasmon resonance, photoelectric effect or catalytic activity were expected to occur. Excellent LDI abilities were seen for Pd-NPs immobilized on steel, while Pd nanoflowers on porous silicon exhibited several disadvantages; viz, strong memory effects, dependency of the analytical signal on amount of physically and chemically adsorbed water inside porous carrier, reduced SALDI activity from unstable connections between Pd and semiconductor material, decrease of the melting point of pure silicon after Pd immobilization and resulting strong laser ablation of metal/semiconductor complex, as well as significantly changed surface morphology after laser irradiation. The analytical performance of Pd-NP/steel was further improved by applying a hydrophobic coating to the steel surface before galvanic deposition. This procedure increased the distance between Pd-NPs, thus reducing thermal stress upon LDI; it simultaneously decreased spot sizes of deposited sample solutions.

Modeling of High-Temperature Low-Pressure Silicon-Refining Process

An improved method for the modeling of the impurity reduction factor during high-temperature low-pressure silicon treatment is suggested. The implementation of a modified logistic function in a mathematical model allows it to be utilized for any range of treatment temperatures. The new model defines the maximum reduction factor for each impurity element present in liquid silicon and defines a critical treatment temperature value. Evaporation increase constant, with high adaptability for the implementation of new process parameters, indicated rapid increase in impurity removal at treatment temperatures slightly above melting point of silicon. Various statistical parameters for the logistic regression method were considerably lower for the 16 studied impurity elements than for the linear or logarithmic correlations.

Spark plasma sintering synthesis of intermetallic T2 in the Mo–Si–B system

Mo5SiB2 (T2) was synthesized by sparking plasma sintering (SPS) under different heating rates and sintering temperatures. The powder mixture with a T2 composition (Mo–12.5Si–25B (at.%)) failed to produce the T2 single-phase alloy due to the volatilization of Si during SPS process. Extra 0.5at.% Si added to this mixture offset the volatilization loss. It has been found that heating of the mixture at low heating rates favored the formation of binary phases in the solid state at medium temperatures. In this work, the T2 alloy with a fine-grained microstructure was obtained via a liquid–solid reaction when the mixture was heated fleetly to the temperatures above the silicon melting point at the rapid heating rate of 200°C/min. The sintering temperature at 1500°C for T2 synthesis is beneficial to enhance further densification, as well as to avoid abnormal grain growth at higher temperatures.

Effect of Organic Additives on Silicon Combustion in Nitrogen

&lt;p&gt;The work shows some peculiarities of silicon combustion in nitrogen in the presence of additives of organic compounds. Organic compounds with different composition were used. Combustion of samples was carried out in a constant-pressure bomb. The combustion products are composite powders and containing α-,β- Si&lt;sub&gt;3&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt;, SiC, Si&lt;sub&gt;2&lt;/sub&gt;N&lt;sub&gt;2&lt;/sub&gt;O. The addition of organic additives suppressed coagulation of Si particles, improved the extent of conversion, and promoted combustion of coarse Si powders which can’t be ignited by any other methods. Introduction of organic dopants to Si powders was found to intensify their combustion without significant influence on the combustion temperature. Active transition of silicon to the gas phase occurs in the low-temperature zone of the combustion wave at the temperature lower than the melting point of silicon. At the temperatures lower than the melting point of Si the quenched combustion products contain two types of crystals of SiC and Si&lt;sub&gt;3&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt;. SiC is formed within a low-temperature zone of the combustion wave. SiC is formed by fine crystals and large spherical particulates which are formed by a bunch of very thin web-like crystals. SiC and Si&lt;sub&gt;3&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt; formation provides a protective coating on silicon particles. It prevents coagulation at the temperature increase. The experiments have proved that it is enough to introduce 1-7 M of the organic additive to 1000 M of silicon for the combustion initiation. Meanwhile, adding different inorganic salts, including ammonium chloride, did not promote combustion. After initiation of combustion to continue Si&lt;br /&gt; powder must contain additives or organic compounds or addition of carbon black; carbon black is necessary for keeping the combustion on.&lt;/p&gt;