Silicon Layer Research Articles

Optimization of the quality factor and sensitivity of one-dimensional photonic crystal methane sensor with cryptophane A cavity

In this work, we introduce a sensor for measuring different methane concentration levels. The model is based on a defective one-dimensional photonic crystal composed of alternating layers of air and Silicon with a cryptophane A cavity. We assume that the refractive index of silicon depends on temperature. The transmittance spectrum was calculated using the transfer matrix method. This work also assessed the effects of temperature and methane concentration on the wavelength shift of a localized mode within the photonic band gap. The results show the shift of this localized mode toward longer wavelengths as temperature increases, with the quality factor reaching its maximum value at around 8994.35. When maintaining a constant temperature, we observed a blue-shift when the methane concentration is in a range of 0.0–3.5%, and the quality factor decreases to 6358.26, with a maximum sensitivity of 144.485 nm by RIU. Due to its excellent performance to store energy within the cavity, this sensor can be used to detect different gas concentrations.

Effect on passivation mechanism and properties of HfO2/crystalline-Si interface under different annealing atmosphere

Hafnium oxide (HfO2) thin film has received tremendous research interests as a passivation layer of crystalline silicon (c-Si) due to its thermal stability and positive fixed charges. HfO2 films were prepared both on P-type and N-type polished c-Si via a remote plasma atomic layer deposition process. Post annealing was carried out in oxygen, atmosphere (Air) and nitrogen (N2) at temperature of 500 °C. Electrical characterization was done through a regular metal-insulator-semiconductor structure and capacitance-voltage measurements. The oxide fixed charge (Qf) and density of interface traps (Dit) between HfO2 and c-Si were extracted. Qf and Dit reveal the potential of HfO2 for field effect and chemical passivation, respectively. Effective lifetime measurements by microwave photoconductivity decay in Si wafers passivated with HfO2 were applied to characterize surface recombination velocity to directly evaluate the overall passivation quality. The impacts of post-annealing gas ambient on passivation qualities on Si by HfO2 thin films are systematically studied. The results show that N2-annealed sample possesses the highest Qf of 1.73 × 1012 cm−2 and therefore provides the best field effect passivation. Air-annealed sample has lowest Dit of 1.0 × 1012 eV−1cm−2 and therefore provides the best chemical passivation. Air-annealed sample possesses the highest effective lifetime of 290 μs at injection level of 1 × 1015 cm−3, which means that good passivation was obtained for N-type Si wafer passivated with HfO2 after annealing in Air.

Highly sensitive asymmetric and symmetric cancer sensors with ultra-high-quality factor and resolution power

In the paper, we proposed two new highly sensitive and compact biosensors with ultra-high-quality factors based on the 1-D binary photonic crystal (silicon/air thin layer) with a defect layer. The proposed asymmetric and symmetric biosensors have just a few periods (two to five) on both sides of the defect layer and the normal cell group (INOK) and cancer cells group (YD-10B) are considered for the studies. The effects of different parameters including silicon layer thickness, air layer thickness, defect layer thickness, substrate position, number of periods, and light incident angle are considered in the biosensor operation and the biosensors are optimized based on the sensitivity. The results demonstrate that the sensitivity and defect mode wavelength of the sensors are independent of the substrate position. However, the quality factor and FOM of the sensors significantly depend on the substrate position and they are improved significantly in the symmetric sensor (~ 37% improvement in optimum condition). Also, the high sensitivities of the sensors are maintained over a wide range of silicon and air thicknesses, which is a valuable achievement in the manufacturing process. Furthermore, the sensitivity of the optimized biosensors with a defect layer thickness of 10 microns and only two periods reaches S ~ 2811 nm/RIU which is an excellent sensitivity for an optical biosensor.

Efficiency improvement of ternary nanofluid within a solar photovoltaic unit combined with thermoelectric considering environmental analysis

Impacts of environmental parameters and dust deposition on the efficiency of solar panel have been scrutinized in this article. To gain thermal output, trapezoidal cooling channel has been attached in the bottom of the panel incorporating ternary nanofluid. To produce working fluid, water has been mixed with Fe3O4TiO2GO nanoparticles. Also, the arrangement of fins has been considered to grow the cooling rate of the silicon layer. The existence of a thermoelectric layer above the cooling channel leads to higher electrical output. Efficacy of ambient temperature (Ta), speed of wind (Vwind) and inlet temperature (Tin) and velocity (Vin) of ternary nanofluid on performance of PVT has been assessed. As Tin increases, electrical efficiency declines about 3.63%. Increase of ambient temperature makes thermal performance enhance about 33.46%. The PVT efficiency decreases about 13.14% and 16.6% with augment of wind speed and dust deposition. CO2 mitigation has been uced about 15.49% in presence of dust while it increases about 17.38% with growth of ambient temperature.

Electronic structure of boron and aluminum δ-doped layers in silicon

Recent work on atomic-precision dopant incorporation technologies has led to the creation of both boron and aluminum δ-doped layers in silicon with densities above the solid solubility limit. We use density functional theory to predict the band structure and effective mass values of such δ layers, first modeling them as ordered supercells. Structural relaxation is found to have a significant impact on the impurity band energies and effective masses of the boron layers, but not the aluminum layers. However, disorder in the δ layers is found to lead to a significant flattening of the bands in both cases. We calculate the local density of states and doping potential for these δ-doped layers, demonstrating that their influence is highly localized with spatial extents at most 4 nm. We conclude that acceptor δ-doped layers exhibit different electronic structure features dependent on both the dopant atom and spatial ordering. This suggests prospects for controlling the electronic properties of these layers if the local details of the incorporation chemistry can be fine-tuned.

Toward TCO‐Free Silicon Heterojunction Solar Cells: Effect of TCO Layers in Electrical Transport and Stability

The current silicon heterojunction (SHJ) cells utilize indium‐based transparent conductive oxide (TCO) layers for supporting the lateral carrier transport. However, In is a typical rare metal and its consumption in solar cell manufacturing must be minimized for sustainable production. In this work, the possibility to realize high‐efficiency TCO‐free SHJ cells, in which no In‐based material is needed, is examined. It is found that monofacial rear‐junction structure is beneficial to collect minority carriers efficiently without the help of TCO layers, regardless of the wafer polarity. In addition, the contact resistivity of locally metallized area must be minimized for efficient carrier transport. Based on these findings, a TCO‐free SHJ cell showing an efficiency of 22.1%, which is comparable to that of the benchmark SHJ cell with TCO layers, is demonstrated. However, direct metallization of amorphous silicon layers causes the degradation in the photovoltaic property after prolonged annealing, probably due to the metal diffusion into Si. This degradation can be avoided by inserting a thin barrier layer such as a SnO2 layer. It is indicated in these results that it is possible to realize TCO‐free SHJ cells with high initial efficiencies, and the main obstacle is not the efficiency but the long‐term stability.

Perpendicular magnetic anisotropy at room-temperature in sputtered a-Si/Ni/a-Si layered structure with thick Ni (nickel) layers

In the literature, a magnetic “easy” axis perpendicular to the film plane at room temperature (i.e., perpendicular magnetic anisotropy - PMA) has been reported in Ni (nickel) layers with thicknesses below ≈15 nm. In this work, we observed room-temperature PMA in a-Si/Ni/a-Si (where a-Si denotes amorphous silicon) thin film structures with nickel layer thicker than 15 nm. Two layered structures were prepared by DC/RF triode sputtering: [a-Si/Ni/a-Si] sandwich structure and [a-Si/Ni/a-Si]5 multilayer structure. The cross sectional STEM revealed uniform Ni layers with thicknesses of ≈17 nm in [a-Si/Ni/a-Si]5 – multilayer and ≈28 nm in [a-Si/Ni/a-Si] – single-layer whereas amorphous Si layers were ≈15 nm and 170 nm thick, respectively. An amorphous Ni–Si interphase was also observed in the layered structures. The XRD showed patterns for fcc-Ni with dominant (111) orientation. No other crystalline phases were observed in the XRD patterns. To our knowledge, there are no literature reports of easy magnetization direction perpendicular to the film plane at room temperature for Ni layers with thickness of ≈28 nm as presented in this work. The origin of PMA in a-Si/Ni/a-Si films may be mainly attributed to the magnetoelastic anisotropy whereas the secondary source of PMA is believed to be the surface anisotropy and magnetocrystalline anisotropy of [111] columnar grains. Amorphous silicon layers (substrate) do not have a well-defined lattice structure like crystalline substrates. Therefore, they do not induce strains in the nickel layers through lattice mismatch as in the case of epitaxy. The strains can be caused by other factors such as diffusion-induced strain, thermal expansion mismatch or intrinsic stresses during the growth process. These results could be important for applications in memory devices, sensors, logic chips, magneto-optic, magneto-electronic and spintronic devices and in fundamental research, as well as first step toward preparation and understanding of the PMA in thick nickel layers.

Metal‐Organic Framework Reinforced Highly Stretchable and Durable Conductive Hydrogel‐Based Triboelectric Nanogenerator for Biomotion Sensing and Wearable Human‐Machine Interfaces

AbstractFlexible triboelectric nanogenerators (TENGs) with multifunctional sensing capabilities offer an elegant solution to address the growing energy supply challenges for wearable smart electronics. Herein, a highly stretchable and durable electrode for wearable TENG is developed using ZIF‐8 as a reinforcing nanofiller in a hydrogel with LiCl electrolyte. ZIF‐8 nanocrystals improve the hydrogel's mechanical properties by forming hydrogen bonds with copolymer chains, resulting in 2.7 times greater stretchability than pure hydrogel. The hydrogel electrode is encapsulated by microstructured silicone layers that act as triboelectric materials and prevent water loss from the hydrogel. Optimized ZIF‐8‐based hydrogel electrodes enhance the output performance of TENG through the dynamic balance of electric double layers (EDLs) during contact electrification. Thus, the as‐fabricated TENG delivers an excellent power density of 3.47 Wm–2, which is 3.2 times higher than pure hydrogel‐based TENG. The developed TENG can scavenge biomechanical energy even at subzero temperatures to power small electronics and serve as excellent self‐powered pressure sensors for human‐machine interfaces (HMIs). The nanocomposite hydrogel‐based TENG can also function as a wearable biomotion sensor, detecting body movements with high sensitivity. This study demonstrates the significant potential of utilizing ZIF‐8 reinforced hydrogel as an electrode for wearable TENGs in energy harvesting and sensor technology.

Density-Functional Study of the Si/SiO2 Interfaces in Short-Period Superlattices: Structures and Energies

The oxide-semiconductor interface is a key element of MOS transistors, which are widely used in modern electronics. In silicon electronics, SiO2 is predominantly used. The miniaturization requirement raises a problem regarding the growing of heterostructures with ultrathin oxide layers. Two structural models of interface between crystalline Si and cristobalite SiO2 are studied by using DFT-based computer modelling. The structures of several Si/SiO2 superlattices (SL), with layer thicknesses varied within 0.5–2 nm, were optimized and tested for stability. It was found that in both models the silicon lattice conserves its quasi-cubic structure, whereas the oxide lattice is markedly deformed by rotations of the SiO4 tetrahedra around axes perpendicular to the interface plane. Based on the analysis of the calculated total energy of SLs with different thicknesses of the layers, an assessment of the interface formation energy was obtained. The formation energy is estimated to be approximately 3–5 eV per surface Si atom, which is close to the energies of various defects in silicon. Elastic strains in silicon layers are estimated at 5–10%, and their value rapidly decreases as the layer thickens. The elastic strains in the oxide layer vary widely, in a range of 1–15%, depending on the interface structure.

Direct Laser Writing of Diffractive Structures on Bi-Layer Si/Ti Films Coated on Fused Silica Substrates

This paper presents the results of an investigation of direct laser writing on a titanium film with an antireflection capping silicon coating. Bi-layer films were deposited on fused silica substrates using an e-beam evaporation system. Modeling predicted that optical absorption for a bi-layer Si/Ti material can be increased by a factor of ~2 compared to a single-layer Ti film at 532 nm laser writing beam wavelength. It is experimentally proved that rate of thermochemical laser writing on Si/Ti films is at least 3 times higher than that on a single-layer Ti film with comparable thickness. The silicon layer was found to participate in the thermochemical reaction (silicide formation) under laser beam heating, which allows one to obtain sufficient position-dependent phase change (PDPC) of light reflected from exposed and unexposed areas. This results in much larger profile depth measured with a white light interferometer (up to 150 nm) than with an atomic force microscope (up to 25 nm). During direct laser writing on Si/Ti films, there is a broad range of writing beam power within which the PDPC and reflection coefficient for the exposed areas change insignificantly. The possibility of selective development of a thermochemically written pattern on a Ti film by removing the capping silicon layer on unexposed areas in a hot KOH solution is shown.

Modeling and optimization of CuIn1-xGaxSe2/Si1-yGey structure for solar cells applications

A combination of a Copper Indium Gallium Selenide (CIGS) and Silicon (Si) layer has been recognized as an excellent choice for producing heterojunction based solar cells with improved efficiency and low cost processing techniques. The quaternary compound CIGS and silicon (Si) regions exhibit a lattice mismatch of about 5%, which induces a strain and impacts the electronic characteristics of the CIGS/Si heterojunction solar cell. A new viewpoint suggests the integration of a silicon germanium (Si1-yGey) layer in the CIGS/Si region to reduce the impact of lattice mismatch. The objective of this study is to investigate how different gallium and germanium concentrations (xGa and yGe) affect the following factors: lattice mismatch (ε), critical thickness (hc) and absorption coefficient (α)of CIGS/SiGe based solar cells. It also aims to analyze how these concentrations impact the primary parameters used to evaluate solar cell performance such as external quantum efficiency, short circuit current density, fill factor, open circuit voltage and conversion efficiency. The simulation results agree well with the existing theoretical and experimental literature data, confirming the suitability of the physical characteristics employed in this numerical study. By tuning the concentrations of Gallium and Germanium, it is feasible to attain an efficiency of 24% owing to the lattice compensation phenomenon in Si1-yGey layers. These findings hold significant implications for the development and advancement of solar cell technology, as well as for enhancing their conversion efficiency and commercialization.

Investigation of anisotropic textured crystalline silicon surface passivation with intrinsic amorphous silicon layers: role of annealing pressure conditions during passivation recovery

Investigation of anisotropic textured crystalline silicon surface passivation with intrinsic amorphous silicon layers: role of annealing pressure conditions during passivation recovery

Analytic modeling and comprehensive transverse deflection analysis of elastically restrained piezoelectric actuators with silicone layer

The impacts of electro-mechanic-fluid parameters on the transverse deflection behavior of the silicone-based piezoelectric diaphragm (SPD) with translational and rotational elastic edges were investigated. The bottommost silicone layer was assumed to be an elastic plate with uniformly distributed elastic restraints along the edges. The closed-form analytical expression for SPD deflections was derived by using classical laminated plate theory based on Kirchhoff’s plate assumptions. The analytical model was validated by experimental, FE methods and the results of the other study. The deflection responses of SPD were examined according to uniform fluid pressure, electric voltage, elastic parameters, dimensions, and material properties.

Enhanced Sensitivity of Binary/Ternary Locally Resonant Porous Phononic Crystal Sensors for Sulfuric Acid Detection: A New Class of Fluidic-Based Biosensors.

This research presented a comprehensive study of a one-dimensional (1D) porous silicon phononic crystal design as a novel fluidic sensor. The proposed sensor is designed to detect sulfuric acid (H2SO4) within a narrow concentration range of 0-15%. Sulfuric acid is a mineral acid extensively utilized in various physical, chemical, and industrial applications. Undoubtedly, its concentration, particularly at lower levels, plays a pivotal role in these applications. Hence, there is an urgent demand for a highly accurate and sensitive tool to monitor even the slightest changes in its concentration, which is crucial for researchers. Herein, we presented a novel study on the optimization of the phononic crystal (PnC) sensor. The optimization process involves a comparative strategy between binary and ternary PnCs, utilizing a multilayer stack comprising 1D porous silicon (PSi) layers. Additionally, a second comparison is conducted between conventional Bragg and local resonant PnCs to demonstrate the design with the highest sensitivity. Moreover, we determine the optimum values for the materials' thickness and number of periods. The results revealed that the ternary local resonant PnC design with the configuration of {silicone rubber/[PSi1/PSi2/PSi3]N/silicone rubber} is the optimal sensor design. The sensor provided a super sensitivity of 2.30 × 107 Hz for a concentration change of just 2%. This exceptional sensitivity is attributed to the presence of local resonant modes within the band gap of PnCs. The temperature effects on the local resonant modes and sensor performance have also been considered. Furthermore, additional sensor performance parameters such as quality factor, figure of merit, detection limit, and damping rate have been calculated to demonstrate the effectiveness of the proposed liquid sensor. The transfer matrix method was utilized to compute the transmission spectra of the PnC, and Hashin's expression was employed to manipulate the porous silicon media filled with sulfuric acid at various concentrations. Lastly, the proposed sensor can serve as an efficient tool for detecting acidic rain, contaminating freshwater, and assessing food and liquid quality, as well as monitoring other pharmaceutical products.

Kinetics of charge carriers in bilateral macroporous silicon

The kinetics of charge carriers in bilateral macroporous silicon with macroporous layers of equal thicknesses is calculated by the finite difference method. A diffusion equation for a monocrystalline substrate and macroporous layers is solved. The boundary conditions are defined at the boundaries between the monocrystalline substrate and the macroporous silicon layers on both sides. Stationary distribution of excess charge carriers in the bilateral macroporous silicon with the macroporous layers of equal thicknesses calculated by the finite difference method is set as the initial condition. Under stationary conditions, excess charge carriers are generated by light with the wavelengths of 0.95 µm and 1.05 µm. It is shown that at the counting times much longer than the relaxation time, all the distributions of the concentration of excess minority carriers generated by light with any wavelength approach the same distribution with exponentially decreasing value.

Alteration and interrogation of ultra-thin layer of silicon by reactive molecular ion implantation

We report the engineering of ultrathin top layer of Si substrate by low energy (14 keV) reactive ion bombardment. The physicochemical nature of the layer is interrogated and the optical properties are explored. Irradiation of nitric oxide (NO+) and mixture of carbon monoxide & nitrogen (CO+ + N2+) ions on Si surface at normal incidence leads to formation of multiple chemical phases of Si with varying ion distribution within the layer. It is found that the chemistry of the topmost layer (∼5 nm) is massively modified by the reactive projectiles, while implanted rich layer is formed at a depth of 25 to 37 nm followed by an intermediate amorphous Si layer of 20 nm thickness. The Ultra Violet-Infrared (UV-IR) response of the modified layer reveals high sensitivity in the UV region. The change in optical bandgap, estimated from Kubelka-Munks theory, indicates the presence of multiple direct and indirect bandgaps. The potential applications of such chemically modified multi-layered ultra-thin Si are addressed here.

Antireflection and radiative cooling difunctional coating design for silicon solar cells.

Passive daytime radiative cooling (PDRC) as a zero-energy consumption cooling method has broad application potential. Common commercial crystalline silicon (c-Si) solar cell arrays suffer working efficiency loss due to the incident light loss and overheating. In this work, a radiative cooler with PDMS (polydimethylsiloxane) film and embedded SiO2 microparticles was proposed to use in silicon solar cells. Both anti-reflection and radiative cooling performance can be improved through numerical parametric study. For the best performing of PDMS/SiO2 radiative cooler, the thickness of PDMS layer, volume fraction and radius of the embedded SiO2 particles have been determined as 55 µm, 8% and 500 nm, respectively. 94% of emissivity in first atmospheric window band (8-13 µm) for radiative cooling and 93.4% of solar transmittance at the crystalline silicon absorption band (0.3-1.1 µm) were achieved. We estimated that the PDMS/SiO2 radiative cooler can lower the temperature of a bare c-Si solar cell by 9.5°C, which can avoid 4.28% of efficiency loss. More incident light can enter and be utilized by silicon layer to enhance the efficiency of the solar cells. The proposed difunctional radiative cooling coating may become guidance for next generation encapsulation of crystalline silicon solar cells.

Effects of friction properties and rheological structures on the deformation patterns and evolution of fold-and-thrust belts—New insights from analogue modelling

Studying fold-and-thrust belts is crucial in geoscience; fold-and-thrust belts are rich in petroleum and natural gas. However, the effects of friction properties and rheological structures on the deformation patterns and evolution of fold-and-thrust belts with two detachment layers are less frequently discussed. Therefore, using models with a basal silicone layer, a middle silicone layer and overlying quartz sand layers, this study conducted an analogue modelling analysis of the effects of friction conditions, rheological structures and compressional velocity on the deformation and evolution of fold-and-thrust belts. The results show the following. 1) The weak layer or low friction strength of the basement forms complex deformations of the structural style, forming forward thrust, backward thrust, symmetrical pop-up structure and frontward–backward oscillating structural characteristics. 2) The friction strength ratio between the lateral and basement layers does not determine the structural style of a fold-and-thrust belt; moreover, it is closely related to the construction of strata or rheological structures. 3) The deformation of double detachment layers complicates the structural style of fold-and-thrust belts. 4) The analogue modelling results are similar to the structural style of the simple fold belt of the Zagros fold-and-thrust belt (ZFTB), indicating that deep and middle detachment layers control the current deformation of the ZFTB.

Evolution of the Microstructure and Mechanical Performance of As-Sprayed and Annealed Silicon Coating on Melt-Infiltrated Silicon Carbide Composites.

In this study, silicon coating was deposited on melt-infiltrated SiC composites using atmospheric plasma spraying and then annealed at 1100 and 1250 °C for 1-10 h to investigate the effect of annealing on the layer. The microstructure and mechanical properties were evaluated using scanning electron microscopy, X-ray diffractometry, transmission electron microscopy, nano-indentation, and bond strength tests. A silicon layer with a homogeneous polycrystalline cubic structure was obtained without phase transition after annealing. After annealing, three features were observed at the interface, namely β-SiC/nano-oxide film/Si, Si-rich SiC/Si, and residual Si/nano-oxide film/Si. The nano-oxide film thickness was ≤100 nm and was well combined with SiC and silicon. Additionally, a good bond was formed between the silicon-rich SiC and silicon layer, resulting in a significant bond strength improvement from 11 to >30 MPa.

Numerical investigation of photovoltaic thermal energy efficiency improvement using the backward step containing Cu-Al2O3 hybrid nanofluid

The increasing demand for renewable energy sources, such as photovoltaic thermal systems, requires efficient cooling techniques to improve performance. Hybrid nanofluids have shown promise in enhancing the cooling performance of such systems. This work seeks to investigate the effect of varying parameters on the performance of a two-dimensional photovoltaic thermal system using hybrid nanofluids for cooling. This work aims to enhance the performance of two-dimensional photovoltaic thermal systems by using hybrid nanofluids for cooling. The hybrid nanofluids use water as their base fluid and contain a mixture of Copper (Cu) and Aluminia oxide. The photovoltaic thermal system is assumed to have a monocrystalline silicon absorber and a backward step as the flow channel. The conduction and forced convection process will occur on the top two layers of silicon and absorber, respectively, while forced convection will occur in the flow and heat transmission channel. The finite element software COMSOL 6.0 will be used to simulate the issue using the energy and Navier-Stokes equations in a two-dimensional, incompressible, and steady-state problem. A parametric study will be conducted by varying the inlet temperature, Reynolds number, volume fraction of Copper, and height downstream of the backward step channel. The results will be verified using a mesh-independent study and the heat transfer coefficient from the available literature. The study demonstrates that increasing the amount of Cu in the base fluid, the upstream channel's channel height and the corresponding Reynolds number improves the performance of the photovoltaic thermal system.