Amorphous Silicon Research Articles

Breaking the Trade-Off Between Mobility and On-Off Ratio in Oxide Transistors.

Amorphous oxide semiconductors (AOS) are pivotal for next-generation electronics due to their high electron mobility and excellent optical properties. However, In2O3, a key material in this family, encounters significant challenges in balancing high mobility and effective switching as its thickness is scaled down to nanometer dimensions. The high electron density in ultra-thin In2O3 hinders its ability to turn off effectively, leading to a critical trade-off between mobility and the on-current (Ion)/off-current (Ioff) ratio. This study introduces a mild CF4 plasma doping technique that effectively reduces electron density in 10nm In2O3 at a low processing temperature of 70°C, achieving a high mobility of 104 cm2 V⁻¹ s⁻¹ and an Ion/Ioff ratio exceeding 10⁸. A subsequent low-temperature post-annealing further improves the critical reliability and stability of CF4-doped In2O3 without raising the thermal budget, making this technique suitable for monolithic three-dimensional (3D) integration. Additionally, its application is demonstrated in In2O3 depletion-load inverters, highlighting its potential for advanced logic circuits and broader electronic and optoelectronic applications.

Efficiency enhancement of WSe2/In2S3 solar cell by numerical modeling using SCAPS

Tungsten diselenide (WSe2), a transition metal dichalcogenide (TMDC) compound, is considered a promising material for application in thin film solar cells because of its high carrier transport, tunable band gap, and high absorption coefficient. In this work, solar cell structure comprising FTO/In2S3/WSe2 is modeled using one-dimensional solar cell capacitance simulator (SCAPS-1D) software where wide bandgap widely accessible In2S3 is used as a novel buffer layer instead of toxic CdS buffer layer for WSe2-based solar cell. The effect of thickness, doping concentrations, defect density, radiative recombination coefficient, and the electron and hole capture cross-section are analyzed and optimized. After optimizing the device, the effect of operating temperature, shunt and series resistance and back contact work function are also investigated. At an optimized WSe2 absorber layer thickness of 1.5 µm and acceptor density of 1017 cm−3, efficiency of 22.53%, fill factor of 84.98%, open circuit voltage of 1.096 V, and short circuit current density of 24.18 mA/cm2 was obtained. Additionally, a back surface field (BSF) layer comprising amorphous silicon (a-Si) of thickness 0.05 µm is introduced between the absorber layer and the back contact to lessen carrier recombination at the back surface. Therefore, the efficiency rises from 22.53% to 29.5% with a fill factor of 89.53%, open circuit voltage of 1.26 V, and short circuit current density of 26.23 mA/cm2. The simulation results suggest that WSe2-based thin-film solar cells can be designed and fabricated with high efficiency and cost advantage.

Development of an Indoor Line Scanning System for Photovoltaic Modules Performance Characterization

Uganda’s interest in using solar energy for various applications began 20 years ago. However, there have been numerous reports by the public over the poor performance of the photovoltaic (PV) modules during their operations. This study determined the performance of selected PV modules openly sold in the Ugandan markets. The low-cost indoor line scanning system developed using locally available materials was used to assess the performance of each of the solar cells in the PV module by determining their photogenerated currents. In addition, the electrical characteristics of the PV modules were determined using the outdoor characterization method, which assumed the actual operation of the PV modules under direct sunlight. From the indoor line scans, the percentage of performing solar cells in the three PV modules of single-crystalline silicon (c-Si), multi-crystalline silicon (mc-Si), and amorphous silicon (a-Si) technologies were determined as 79%, 61%, and 95% respectively. The outdoor characterization results revealed that the c-Si, mc-Si, and a-Si PV modules had measured maximum power outputs of 18.5 W, 19.0 W, and 18.9 W, respectively and these were lower than the rated power values of 20 W. The line scan results had a direct relationship with the measured power output of the PV module, which implied that solar cells mismatch, affected the performance of the PV modules by lowering their performance. This developed testing system is affordable for developing countries with limited testing systems and would in the long run contribute to significant increase in the deployment of PV technology in Uganda since only performing PV modules would be allowed into the open market.

Bioactive Properties of Phosphate-Modified Silicon Oxycarbide Protective Coatings: Morphology and Functional Evaluation.

This article presents a study on the functional properties and morphology of coatings based on amorphous silicon oxycarbide modified with phosphate ions and comodified with aluminum and boron. The objective of this modification was to enhance the biocompatibility and bioactivity without affecting its protective properties. The comodification was aimed toward stabilization of phosphate in the structure. The coatings were prepared according to the typical procedure for polymer-derived ceramics: synthesized via the sol-gel method, deposited using the dip-coating technique, and subsequently pyrolyzed. Comprehensive analyses of the morphology, surface properties, corrosion resistance, and bioactivity were conducted to assess their functional performance. The coatings exhibited uniform and smooth surfaces, with phase separation observed in the boron-modified SiBPOC series. Surface wettability and free energy measurements demonstrated that SiPOC and SiBPOC coatings possessed moderate hydrophilicity and favorable surface free energy for cell adhesion and bone tissue mineralization. Corrosion resistance tests in Ringer's solution revealed that SiBPOC coatings provided the highest protection against ion leaching, while SiAlPOC showed decreased resistance due to surface cracks. Bioactivity tests indicated calcium phosphate precipitation on the surface of all samples with higher hydroxyapatite formation on SiPOC and SiAlPOC coatings. In vitro tests using MG-63 osteoblast-like cells confirmed the biocompatibility of the coatings, with SiPOC and SiBPOC exhibiting the best combination of bioactivity, cell adhesion, and proliferation. These findings suggest that the phosphate- and boron-modified SiOC-based coatings are promising candidates for enhancing bone integration in orthopedic implants.

High-Temperature Stable Amorphous Sn-Rich InSnGaO Thin Films Fabricated Via Atomic Layer Deposition for Next-Generation Dynamic Random-Access Memory Applications.

Facile phase transitions and electrical degradation of amorphous oxide semiconductors due to a high thermal budget have significantly limited their dynamic random-access memory (DRAM) applications, which require high thermal stability at temperatures over 600 °C. In this paper, we report an amorphous In-Sn-Ga-O (ITGO) semiconductor fabricated via atomic layer deposition, which exhibits high-temperature (∼700 °C) phase stability with moderate electrical properties. The optimal Sn-rich ITGO composition (In/Sn/Ga = 25:58:17 at. %) represents a thermally stable amorphous phase with excellent Hall mobility (24.0 cm2/(V s)) above 600 °C. Various analytical and simulation methods reveal the role of Sn as an efficient amorphous stabilizer and enhancer of electron mobility in oxide semiconductors. A thin-film transistor with a 4.5 nm-thick ITGO channel demonstrates excellent field-effect mobility (7.7 cm2/(V s)) and reliability. Therefore, Sn-rich ITGO is a promising candidate for next-generation DRAM channels that require amorphous-phase stability at a high thermal budget.

Multiscale modeling of short pulse laser induced amorphization of silicon

Silicon surface amorphization by short pulse laser irradiation is a phenomenon of high importance for device manufacturing and surface functionalization. To provide insights into the processes responsible for laser-induced amorphization, a multiscale computational study combining atomistic molecular dynamics simulations of nonequilibrium phase transformations with continuum-level modeling of laser-induced melting and resolidification is performed. Atomistic modeling provides the temperature dependence of the melting/solidification front velocity, predicts the conditions for the transformation of the undercooled liquid to the amorphous state, and enables the parametrization of the continuum model. Continuum modeling, performed for laser pulse durations from 30 ps to 1.5 ns, beam diameters from 5 to 70 μm, and wavelengths of 532, 355, and 1064 nm, reveals the existence of two threshold fluences for the generation and disappearance of an amorphous surface region, with the kinetically stable amorphous phase generated at fluences between the lower and upper thresholds. The existence of the two threshold fluences defines the spatial distribution of the amorphous phase within the laser spot irradiated by a pulse with a Gaussian spatial profile. Depending on the irradiation conditions, the formation of a central amorphous spot, an amorphous ring pattern, and the complete recovery of the crystalline structure are predicted in the simulations. The decrease in the pulse duration or spot diameter leads to an accelerated cooling at the crystal–liquid interface and contributes to the broadening of the range of fluences that produce the amorphous region at the center of the laser spot. The dependence of the amorphization conditions on laser fluence, pulse duration, wavelength, and spot diameter, revealed in the simulations, provides guidance for the development of new applications based on controlled, spatially resolved amorphization of the silicon surface.

Elucidating the Morphology of Partially Lithiated Microscale Silicon Particles using Transmission Electron Microscopy

Abstract Partial lithiation of silicon active materials for lithium-ion batteries recently gained attention as a promising mitigation strategy for the degradation phenomena associated with the severe volume expansion upon the lithiation, particularly in the case of large, microscale silicon particles. It was suggested that this is caused by the formation of a stabilizing core-shell-like particle structure in the first cycles, consisting of a crystalline core and amorphous silicon shell. In this study, we investigated the microstructure of partially lithiated microscale silicon particles using transmission electron microscopy (TEM). When observed via TEM, the contrast difference in amorphous and crystalline silicon is utilized to reveal previously lithiated areas inside the silicon microparticle. We investigated the influence of lower cutoff potentials and amorphization progress in half-cells. We also examined the changes over prolonged cycling in full-cells with an NCA cathode after 12 and 243 cycles. Silicon particle pulverization was not observed for any sample, even though we found that substantial parts of the particles' insides had been lithiated. We suggest that the diffusion of Li along grain boundaries and stacking faults plays an essential part in the amorphization and cycling of microscale Si particles but does not lead to their cracking or pulverization.

Design, fabrication, and performance analysis of a silicon solar cell integrated transparent antenna for wireless communications

The solar cell integrated transparent antenna will serve the purpose of power generation as well as an antenna for satellites and can act as an asset to expand the possibilities of green technology. The goal is to enhance antenna characteristics without hampering solar cell performance. In this work, a super solar integrated optically transparent microstrip patch antenna has been studied using CST Microwave Studio along with Lumerical FDTD and DEVICE solutions. The optically transparent antenna has a Soda-lime glass substrate, with Indium Tin Oxide patch and ground plane. The fabricated antenna is integrated with a 25 × 40 mm2 thin-film silicon solar cell via epoxy resin. UV–Vis spectroscopy results revealed more than 90% transmissivity over a significant visible wavelength range. It has an operational bandwidth of 80 MHz (@5.48 GHz) and solar simulator results indicate that the photovoltaic performance of the proposed device is similar to that of a standalone solar cell.

Nonlinear Elasticity of Amorphous Silicon and Silica from Density Functional Theory

Nonlinear Elasticity of Amorphous Silicon and Silica from Density Functional Theory

Optomechanical microgear cavity

We introduce a novel optomechanical microgear cavity for both optical and mechanical isotropic materials, featuring a single-etch configuration. The design leverages a conjunction of phononic and photonic crystal-like structures to achieve remarkable confinement of both optical and mechanical fields. The microgear cavity we designed in amorphous silicon nitride exhibits a mechanical resonance at 4.8 GHz, and whispering gallery modes in the near-infrared, with scattering-limited quality factors above the reported material limit of up to 107. Notably, the optomechanical photoelastic overlap contribution reaches 75% of the ideal configuration seen in a floating ring structure.

Reliable Prediction of Solar Photovoltaic Power and Module Efficiency using Bayesian Surrogate Assisted Explainable Data-Driven Model

This study proposes a Bayesian surrogate-driven explainable deep neural network model to predict and interpret the module efficiency and maximum output power of three commercially available photovoltaic modules: monocrystalline silicon, polycrystalline silicon, and amorphous silicon during the winter season. In addition, the influence of the photovoltaic material and ambient conditions on the predicted power and module efficiency is investigated. The model inputs include solar irradiance, module material (monocrystalline, polycrystalline, and amorphous silicon), season of the year (months), and time of day (morning to evening). Experiments were conducted on these three modules during the winter using data from Rawalpindi, Pakistan. These data were then fed into the deep neural network model to train and yield predictions. Several preprocessing techniques such as logarithmic transformation, square root, cube root, reciprocal, and exponential transformations are employed to improve the linearity of distributed data. For hyper-parameters optimization, Gaussian process, gradient boost regression trees, and random forest are used. The results show that the optimal deep neural network using random forest surrogate model along with square root and exponential transformation is able to predict the maximum power output and module efficiency of the considered photovoltaic modules for the entire investigated period with a correlation coefficient, R2 = 0.998. The least accurate model (R2=0.991) is a Gaussian process using simple data distribution. These results hold valuable insights for predicting and optimizing the performance of other solar photovoltaic modules in various climates and different seasons of the year.

Effect of doping with M (M=Al, Pd, Ti, Ge) on the electronic structure and hydrogen diffusion behavior of amorphous silicon

Amorphous silicon (a-Si) models doped with Pd, Ge, Al, and Ti (a-Si/M) at three different doping ratios are generated using Ab initio Molecular Dynamics (AIMD) high-temperature annealing, followed by analysis utilizing first-principles method. The electronic structure calculations reveal strong interactions between Al, Ge and Si, while interaction between Pd, Ti and Si are relatively weak. Moderate doping of Pd and Ti can reconstruct the a-Si surface, reduce the adsorption energy of H on the surface, and increase the Si-Si atomic gap. This will greatly reduce the energy barrier for H to diffuse on the surface and to the subsurface.

A multi-functional platform for stimulating and recording electrical responses of SH-SY5Y cells.

In recent years, multifunctional cell regulation on a single chip has become an imperative need for cell research. In this study, a novel multi-functional micro-platform integrating wireless electrical stimulation, mechanical stimulation and electrical response recording of cells was proposed. Controlling cell fate by photoexcited radio stimulation of cells on photosensitive films can precisely orchestrate biological activities. This is the first report of combining hydrogenated amorphous silicon (a-Si:H) photosensitive films and a 532 nm green laser for cell stimulation and electrical response recording. Remote wireless electrical stimulation of nerve cells through photoelectric effects based on photosensitive films evoked a change in membrane potential and promoted the neurite growth and neuronal differentiation. These effects were confirmed in a cell model of the human neuroblastoma cell line. The electrical response of cells demonstrated that the photocurrent generated by laser irradiation of the photosensitive film induced a redistribution of ions inside and outside the cell. Furthermore, a mechanical stimulus was applied to cells using a probe placed above them. The chip was used as a signal output to simultaneously obtain the electrical response of cells. The ability of photosensitive films to precisely excite cellular activity offers a novel prospect for wireless electrical stimulation. This work provides a promising strategy for the design of multi-functional biological devices based on a single chip.

Sputtered Amorphous Silicon Thin Films Exhibiting Low Argon Working Gas Content and High Film Density

Sputtered Amorphous Silicon Thin Films Exhibiting Low Argon Working Gas Content and High Film Density

Accurate Method for Solar Power Generation Estimation for Different PV (Photovoltaic Panels) Technologies

In 2023, solar photovoltaic energy alone accounted for 75% of the global increase in renewable capacity. Moreover, this natural energy resource is the one that requires the least investment, which makes it accessible to developing countries. Increasing return on investment in these regions requires a particular evaluation of environmental parameters influencing PV systems performance. Higher temperatures decrease PV module efficiency and, as a result, their power output. Additionally, fluctuations in solar irradiance directly impact the energy generated by these systems. Consequently, it is essential for investors to improve accurate predictive models that assess the power generation capacity of photovoltaic systems under local environmental conditions. Therefore, accurate estimation of maximum power generation is then crucial for optimizing photovoltaic (PV) system performances and selecting suitable PV modules for specific climates. In this context, this study presents an experimental comparison of three maximum power prediction methods for four PV module types (amorphous silicon, monocrystalline silicon, micromorphous silicon, and polycrystalline silicon) under real outdoor conditions. Experimental data gathered over the course of a year are analyzed and processed for the four PV technologies. Three different methods taking into account environmental parameters are presented and analyzed. The first estimation method utilizes irradiance as the primary input parameter, while two additional methods incorporate ambient temperature and PV module temperature for enhanced accuracy. The performance of each method is evaluated using standard statistical metrics, including the root mean square error (RMSE) and coefficient of determination (R2). The results demonstrate the effectiveness of all three methods, with RMSE values ranging from 1.6 W to 3.8 W and R2 values consistently above 0.95. The most appropriate method for estimating PV power output is determined by the specific type of photovoltaic module and the availability of meteorological parameters. This study provides valuable insights for selecting an appropriate maximum power prediction method and choosing the most suitable PV module for a given climate.

Kinetic study of a-Si crystallization induced by an intermetallic compound

The problem under study is concerned with amorphous silicon (a-Si) crystallization which is induced by an intermetallic compound, with this compound chosen to be Al2Cu, formed by a solid-state reaction between nanolayers of aluminum and copper in a Cu/Al/a-Si multilayer system. In the case of crystallization initiated by the intermetallic compound Al2Cu, the crystallization temperature of amorphous silicon was found to be ≈ 300°С (upon heating at a rate of 5–10 °C/min), which was significantly higher than in the case of pure Al (≈170°С), but lower as compared to using pure Cu (≈485°С). The higher crystallization temperatures in comparison with aluminium-induced crystallization are assumed to be caused by a decrease in the number of free electrons due to the presence of copper and formation of the Al2Cu phase. By kinetic modeling, it was revealed that the mechanism of a-Si crystallization induced by the intermetallic compound Al2Cu was similar to the mechanism of Al-induced crystallization of a-Si in multilayer (Al/a-Si)n films, i.e the process of a-Si crystallization occurred in two subsequent stages: Cn-X→Fn. Kinetic parameters of silicon crystallization for each reaction step were obtained. The enthalpy of a-Si crystallization initiated by Al2Cu was estimated to be ΔH = 12.3 ± 0.5 kJ/mol.

Description of excitonic absorption using the Sommerfeld enhancement factor and band-fluctuations

Abstract One of the challenges of excitonic materials is the accurate determination of the exciton binding energy and bandgap from optical measurements. The difficulty arises from the overlap of the discrete and continuous excitonic absorption at the band edge. Many researches have modeled the shape of the absorption edge of such materials on the seminal formulation proposed by Elliott in 1957 (Phys. Rev. 108 1384–9) and its several modifications such as non-parabolic bands, magnetic potentials and electron–hole-polaron interactions. However, exciton binding energies obtained from optical absorption often vary strongly depending on the chosen ‘Elliott formula’. Here, we propose an alternative and rather simple approach, which has previously been successful in the determination of the optical bandgap of amorphous, direct and indirect semiconductors, based on the band-fluctuations (BFs) model. In this model, the fluctuations due to disorder, temperature or lattice vibrations give rise to the well known exponential shape of band tail states. The formulation results in an analytic equation for the fundamental absorption with 6 parameters only. To test it, the binding energy and optical bandgap of GaAs and the family of tri-halide perovskites ( MAPbX 3 ), X = Br , I , Cl , over a wide range of temperatures, are obtained by fitting the modified Elliott model. The results for the bandgap, linewidth and exciton binding energy are in good agreement with reports based on non-optical measurements. Moreover, due to the polar nature of perovskites, the retrieved binding energies can be compared with those computed with a model proposed by Kane (1978 Phys. Rev. B 18 6849). In the latter model, the exciton is surrounded by a cloud of virtual phonons interacting via the Frölich interaction. As a consequence, the upper bound for the binding energy of the exciton-polaron system can be estimated. These results are in good agreement with the optical parameters obtained with the proposed Elliott equation including BFs.

Slow Voltage Relaxation of Silicon Nanoparticles with a Chemo-Mechanical Core-Shell Model.

Silicon presents itself as a high-capacity anode material for lithium-ion batteries with a promising future. The high ability for lithiation comes along with massive volume changes and a problematic voltage hysteresis, causing reduced efficiency, detrimental heat generation, and a complicated state-of-charge estimation. During slow cycling, amorphous silicon nanoparticles show a larger voltage hysteresis than after relaxation periods. Interestingly, the voltage relaxes for at least several days, which has not been physically explained so far. We apply a chemo-mechanical continuum model in a core-shell geometry interpreted as a silicon particle covered by the solid-electrolyte interphase to account for the hysteresis phenomena. The silicon core (de)lithiates during every cycle while the covering shell is chemically inactive. The visco-elastoplastic behavior of the shell explains the voltage hysteresis during cycling and after relaxation. We identify a logarithmic voltage relaxation, which fits with the established Garofalo law for viscosity. Our chemo-mechanical model describes the observed voltage hysteresis phenomena and outperforms the empirical Plett model. In addition to our full model, we present a reduced model to allow for easy voltage profile estimations. The presented results support the mechanical explanation of the silicon voltage hysteresis with a core-shell model and encourage further efforts into the investigation of the silicon anode mechanics.

Influence of Solenopsis invicta Buren on soil chemical properties, silicon pools, and phytolith assemblages in organic agricultural soils

ABSTRACT Ants mediate ecosystem services that can modulate crop performance and overall agroecosystem functioning. Our study investigated how the activity of Solenopsis invicta Buren (Hymenoptera: Formicidae) influences soil chemical properties, soil silicon pools, and soil phytoliths. We hypothesized Solenopsis invicta Buren activity would increase the macronutrient content, available silicon for plants (PASi), and amorphous silicon (ASi) in nest soils, which is related to changes in the phytolith assemblage. This study was conducted on agricultural soil under organic management, covering an area of approximately 70 ha in Rio de Janeiro State, Brazil. Thirty paired soil and nest samples were collected at a depth of 0.20 m and analyzed to obtain values for soil macronutrients and silicon pools (PASi and ASi) and to perform phytolithic analyses. Phytolith extraction from the samples was undertaken using a protocol that involved removed coatings, clay fractions, and iron oxides through density separation, followed by the determination of the phytolith concentration and identification of a minimum of 200 phytoliths per sample using a Zeiss Axioskop 40 optical microscope. Results indicated an increase in total organic carbon (TOC), phosphorus (P), and potassium (K) levels and in all forms of Si studied. Ants also affected phytolith assemblages, and there was an increase in morphotypes associated with dicotyledonous plants in the nest soil. We assumed these results were derived from bioturbation promoted by ants, predatory activity, and the interaction of some prey and phytoliths, leading to biologically enhanced weathering. By uncovering and describing this novel role for a widely distributed and highly abundant organism in Neotropical soils, we propose that these alterations, particularly in the biogeochemical cycle of silicon, should be added to the list of ecosystem services provided by ants. This study presents the first evidence of alterations in silicon pools and phytolith assemblages caused by the action of ants.

Semiconducting biomass-based amorphous carbon films and their potential application in photovoltaic devices

Amorphous carbon (aC) is highly appealing because of its unique structure, electrical and optical properties, making it appropriate for various applications, especially in energy conversion. This work presents a comprehensive study on the synthesis of aC materials, including both intrinsic (i-type) and doped conditions (p- and n-type), to enhance the performance of photovoltaic films. Carbon materials are derived from biomass using a straightforward and environmentally conscious technique. The obtained carbon compound demonstrates an amorphous state with a substantial prevalence of the sp2 C=C component. Raman spectroscopy and electron microscopy confirmed the stacking of 2D layers forming a multilayer graphene structure. The carbon compound prepared AC films deposited onto a quartz glass surface via spray coating. The films have a thickness ranging from 247 to 478 nm. The dielectric constants of the optical parameters reveal resonant exciton features at a photon energy of ∼3.8 eV, whereas the real component exhibits semiconductive properties. The refractive indices of the p-, i-, and n-layers, which have gap energies in decreasing order, demonstrate a decline. The optical conductivity of aC is higher than that of amorphous silicon, specifically 0.54 × 103Ω−1cm−1, 0.48 × 103 Ω−1cm−1, and 0.53 × 103 Ω−1cm−1 for the p-, i-, and n-type films, respectively. Based on this outcome, it is reasonable to suggest that the recently developed material is potentially important as a photovoltaic device.