Ultrathin Silicon Research Articles

Optoelectronic properties of ultrathin ALD silicon nitride and its potential as a hole-selective nanolayer for high efficiency solar cells

Fully exploiting the power conversion efficiency limit of silicon solar cells requires the use of passivating contacts that minimize electrical losses at metal/silicon interfaces. An efficient hole-selective passivating contact remains one of the key challenges for this technology to be deployed industrially and to pave the way for adoption in tandem configurations. Here, we report the first account of silicon nitride (SiNx) nanolayers with electronic properties suitable for effective hole-selective contacts. We use x-ray photoemission methods to investigate ultra-thin SiNx grown via atomic layer deposition, and we find that the band alignment determined at the SiNx/Si interface favors hole transport. A band offset ratio, ΔEC/ΔEV, of 1.62 ± 0.24 is found at the SiNx/Si interface for the as-grown films. This equates to a 500-fold increase in tunneling selectivity for holes over electrons, for a film thickness of 3 nm. However, the thickness of such films increases by 2 Å–5 Å within 48 h in cleanroom conditions, which leads to a reduction in hole-selectivity. X-ray photoelectron spectroscopy depth profiling has shown this film growth to be linked to oxidation, and furthermore, it alters the ΔEC/ΔEV ratio to 1.22 ± 0.18. The SiNx/Si interface band alignment makes SiNx nanolayers a promising architecture to achieve widely sought hole-selective passivating contacts for high efficiency silicon solar cells.

Screen-printed n-type industry solar cells with tunnel oxide passivated contact doped by phosphorus diffusion

Abstract Tunnel oxide passivated contact (TOPCon) industrial (244.32 cm2) c-Si solar cell is fabricated in this paper. Both the ultra-thin silicon oxide layer and intrinsic polycrystalline silicon layer are deposited by low-pressure chemical vapor deposited (LPCVD). Then intrinsic polycrystalline silicon layers are doped by thermal diffusion of POCl3 in an industrial-scale quartz tube furnace. Experiment conditions like polycrystalline silicon thickness, diffusion temperature, diffusion time and POCL3 flow rate on the passivation quality of TOPCon structure are investigated in detail and low recombination current density ~8 fA/m2 has been achieved for c-Si/SiOx/poly-Si(70 nm)/SiNx structure at diffusion temperature 850 °C. A variation about 30–40 mV has been observed between the iVoc and Voc for 70 nm samples, which should be attributed to the metallization-induced degration. Not consistent with the result obtained from symmetric samples, both an improvement to the solar cell efficiency has been found for 70 nm thick poly-Si and 170 nm thick poly-Si at the diffusion temperature above the optimal diffusion temperature. Finally, by optimizing the polysilion thickness and phosphorus diffusion, the champion solar cell efficiency of 22.81% is achieved, with Voc of 702.6 mV, Jsc of 39.78 mA/cm2, FF of 81.62%.

First-Principles Study of Ultrathin Single-Walled Nanotube-Based Single-Electron Transistor for Fast-Switching Applications

This work presents modeling and functioning of nanotube island single-electron transistor (SET), through first-principles approach based on density functional theory and non-equilibrium Green’s function. Ultrathin single-walled carbon (C), boron nitride (BN), and silicon carbide (SiC) nanotubes in armchair (3, 3) and zigzag (5, 0) structures have been adopted as island in the SET model. The nanotube (NT) islands are weakly coupled to gold metal electrode, explained by sequential transport phenomenon. Present study evaluates ionization energies, electron affinities, and additional energies for all the considered NTs in both isolated and SET environment, which are further analyzed by plotting total energies and Coulomb blockade diagrams. Also, various types of dielectric material and their thickness have been investigated, owing to measuring the stability of charge as well as dependence of conductance on gate and source-drain voltage. Observed results show noticeably enhanced conductance for ultrathin single-walled C, BN, and SiC zigzag NTs than that of their corresponding armchair NTs in the SET systems, demonstrating their potential for fast-switching device applications.

Designing intelligent nano-bomb with on-demand site-specific drug burst release to synergize with high-intensity focused ultrasound cancer ablation

High intensity focused ultrasound (HIFU) has been widely used in clinical treatment of cervical cancer for its non-invasiveness and sharp treatment margins with very low complication rates. However, how to intensify the therapeutic efficacy of HIFU by specifically focusing the ultrasound energy on targeting pathological tissues is still a bottleneck for it to realize successful cancer ablation. Herein, a multifunctional organic-inorganic hybrid nanovesicles, by coating ultrathin silica shell on the surface of poly (lactic-co-glycolic acid) (PLGA) loaded with perfluorocarbon (PFOB), hydrophobic antitumor ruthenium complex (RuPOP) and superparamagnetic Fe3O4, has been designed to achieve synchronous ultrasound (US)/magnetic resonance imaging (MR) dual mode imaging-guided HIFU-triggered chemotherapy. The introduction of PFOB in this nanosystem could cause phase transition and make it gasification to cause collapse of the outer ultrathin silicon shell under HIFU irradiation, which results in enhanced intensive mechanical stress during blasting and enhanced therapeutic effect. The blasting behavior of this nanosystem triggered by HIFU also induced the on-demand RuPOP burst release in tumor site, thus maximizing the inhibition on residual tumor induced by inhomogeneous HIFU ablation. Taken together, this treatment strategy could overcome the inevitable tumor recurrence and significantly reduces systemic side effects of HIFU, thus could be further developed for noninvasive cancer therapy.

Directly Exfoliated Ultrathin Silicon Nanosheets for Enhanced Photocatalytic Hydrogen Production.

Here we present direct exfoliation of ultrathin silicon nanosheets from commercial silicon powders through an improved liquid phase exfoliation procedure. The feasibility of exfoliation was ascribed to the intrinsic anisotropic lattice structure, which allowed the oriented propagations of cryo-mediation-induced quenching cracks with the assistance of sonication. It was also revealed that the solid-solvent interface played a critical role in determining the morphology of exfoliated pieces as well as the exfoliation efficiency. Moreover, due to its superior morphology, enlarged surface area, and improved photon absorption, the resulting ultrathin silicon nanosheets presented enhanced and visible light responsive photocatalytic hydrogen generation performance, even without applying any co-catalyst.

Разработка материалов и радиационно-стойкой ЭКБ на основе КНС/КНИ структур

The article deals with the problems of development and selection of materials based on the structures of KNS/CNI (silicon on insulator/ silicon on sapphire). The article describes the prospects of technology for designing and manufacturing chips based on ultra-thin silicon layers on a sapphire substrate (UTSi). The result of a comparative analysis of modern technologies for manufacturing KNI structures is presented.

Optical field concentrator with low absorption metasurfaces based on planar silicon nanoantennas on silica

Plasmonic metamaterials open a pathway to a multitude of different applications, from ultrasensitive sensors to merging the packaging density of electronics and the speed of photonics in a single all-optical device. A severe limitation to their wider use is high absorption due to the mandatory presence of free electron-containing conductive parts which are lossy by definition. In this contribution we consider an alternative solution in the form of ultrathin silicon films deposited on a silica substrate. The films are patterned as arrays of elongated rhombuses acting as bowtie nanoantennas. We consider the effect of sharp tips and the proximity effect on the electromagnetic field concentration in such low-loss metasurfaces. Our structures have the advantage of very low absorption losses with an order of magnitude field enhancement and the virtue of full compatibility with the standard planar technologies. This makes them convenient for various practical applications which integrate high field concentration with e.g. waveguiding properties, for instance microreactors, labs-on-a-chip, photocatalytic systems and various other Micro-Opto-Electro-Mechanical System (MOEMS) devices integrating optical, microfluidic and other functionalities.

Total absorption for an ultrathin silicon grating within the low-loss mid-infrared window

To increase the absorption of silicon (Si)-based nanostructures within the loss window in the mid-infrared (MIR) range, periodic configuration which can efficiently couple the light into the supported optical modes have been proposed. In the first presentation, the absorption reaches a peak value of 99.6% at 3.162 μm wavelength with an ultra-narrow band. The absorber can be regarded as one-port resonant system with loss that can be explained through coupled mode theory (CMT). The influences of structure parameters on the absorption spectrum have been investigated in detail. In the second sample, vertically cascaded metal-dielectric-metal (MDM) grating structures are introduced to achieve dual-band selective absorbers. The underlying absorption mechanism of such perfect absorption effects at different resonant wavelength is attributed to the hybridization of cavity mode and guide mode resonance (GMR). These types of devices promise to impact the fields of solar thermophotovoltaics and sensing technologies with Si structures. • Spectral control of an ultra-narrow single-band MIR absorber is realized within the low loss window of Si. • Dual-band absorber with near unity absorption are designed suing vertically cascaded MDM grating structures. • Aluminum is used to obtain full compatibility with industry standard CMOS wafer-scale processing technology.

Experimental investigation and simulation of crystallographic orientations evolution in a cold-rolled ultra-thin grain-oriented silicon steel

The evolutions of crystallographic orientations and textures of a cold-rolled ultra-thin grain-oriented silicon steel are studied via experimental investigation, texture simulation and orientation evolution calculation. The experimental results show that all components of η-fiber ({0kl} 〈100〉 ) orientations in raw material demonstrate multi-directional crystal rotation routes during rolling and these initial orientations are retained as small regions distributed within the deformed matrix (mainly {111} 〈112〉 ), and the calculated typical transformation of orientations under the cold rolling condition is in good agreement with the experimental results. The crystal orientation of a grain would rotate to {111} 〈112〉 after rolling as long as its initial orientation is close to or slightly deviates from exact Goss ({011} 〈100〉 ). When the initial orientations deviates towards {021} 〈100〉, the final deformed microstructures mainly turn into deviated γ-fiber or display {113} 〈361〉 orientations, meanwhile the orientation transition along η-fiber (rotating about 〈100〉 axis) during rolling is enhanced. Regarding the effect of surface shear on rolling plane towards rolling direction (RD) in ultra-thin steel production, it is suggested to strengthen {111} 〈112〉 deformation texture. While for different {0kl} 〈100〉 components, the same surface shear exerts varied effect on the crystal rotation route, resulting in multiple orientation transition routes in deviated Goss and {021} 〈100〉 grains under cold-rolling process.

Heavy-flavour Measurements in Pb–Pb Collisions with the Upgraded ALICE Inner Tracking System

During the second LHC long shutdown (LS2) the Inner Tracking System (ITS) of ALICE (A Large Ion Collider Experiment) will be replaced by seven layers of CMOS Monolithic Active Pixel Sensors (MAPS). The latest innovations in silicon imaging technology allow for the construction of large, ultra-thin silicon wafers which can further improve the capabilities of the ALICE tracker. The research and development studies towards the construction of a novel vertex detector have started. The detector installation has been proposed for the third LHC long shutdown (LS3) during which the three innermost layers shall be replaced by three cylindrical layers of large curved CMOS wafers. This upgrade (ITS3) will further improve the impact parameter resolution and the tracking efficiency of low momentum particles. The innermost layer will be positioned closer to the interaction point and the material budget will be reduced down to 0.05$\%X_0$ per layer. Monte Carlo simulations of a simplified ITS3 geometry within the ITS2 design indicate an improvement in the impact parameter resolution and the tracking efficiency, which are of crucial importance for measurements of heavy-flavour hadrons. This contribution shows the improved performance for the example of the $\Lambda_{\mathrm{b}}$, for which the significance of its measurement is extracted based on these MC simulations. A significant improvement by almost a factor of three in the low momentum region compared to the ITS2 is observed.

Simulation of recrystallization based on EBSD data using a modified Monte Carlo model that considers anisotropic effects in cold-rolled ultra-thin grain-oriented silicon steel

A Monte Carlo Potts model was developed to simulate the recrystallization process of a cold-rolled ultra-thin grain-oriented silicon steel. The orientation and image quality data from electron backscatter diffraction measurements were used as input information for simulation. Three types of nucleation mechanisms, namely, random nucleation, high-stored-energy site nucleation (HSEN), and high-angle boundary nucleation (HABN), were considered for simulation. In particular, the nucleation and growth behaviors of Goss-oriented ({011} ) grains were investigated. Results showed that Goss grains had a nucleation advantage in HSEN and HABN. The amount of Goss grains was the highest according to HABN, and it matched the experimental measurement. However, Goss grains lacked a size advantage across all mechanisms during the recrystallization process.

NrGO Floating Gate/SiOXNY Tunneling Layer Stack for Nonvolatile Flash Memory Applications

This paper presents an ultra–thin silicon oxynitride (SiOXNY, 4 nm) tunneling layer, nitrogen functionalized reduced graphene oxide (NrGO, 3–5 layer) floating gate (FG) and poly (methyl methacrylate) (PMMA, 60 nm) blocking layers based Al/PMMA/NrGO/SiOXNY/p–Si/Au, non–volatile flash memory (NVFM) structures. The ultra–thin SiOXNYhelps in improving the interface with Si, resulting in lower gate leakage current density and considerable enhanced retention characteristics. The nitrogen engineered GO followed by reduction to NrGO under UV illumination attributes to the modification of the physiochemical properties, hence beneficial for non-volatile memory applications. The uniform, stress free and low temperature processing advocates the potential of PMMA as blocking layer for improved memory characteristics. The electrical characterizations on the fabricated Al/PMMA/NrGO/SiOXNY/p–Si/Au gate stack demonstrates a memory window ( ${\delta }\text{W}$ ) of ~1.25 V @ ± 3 V and ~2.6 V @ ± 5 V, low gate leakage current density (J) ~10 nA/cm2@ −1 V, retention $\sim 3 \times 10^{11}$ sec (> 10 years with extrapolation) and endurance of more than 100 cycles.

Study on Degradation Mechanisms of Thermal Conductivity for Confined Nanochannel in Gate-All-Around Silicon Nanowire Field-Effect Transistors

In this article, an analytical thermal conductivity model for confined nanochannel in gate-all-around silicon nanowire field-effect transistors (GAA SiNW FETs) is developed by considering the limitations caused by the cross section and length. A geometry dependence of phonon mean free path (MFP) is established for quantitatively analyzing the influence of cross-sectional dimension. Furthermore, the length-induced degradation mechanism is revealed by employing the transverse transportation phonon effective MFP. The results calculated by the model which was verified by published data indicate that the thermal conductivity of confined nanochannel in the GAA SiNW FETs is suffering from a severe degradation compared to that of ultrathin silicon in fully depleted (FD) silicon-on-insulator (SOI) MOSFETs. In addition to the suppression caused by the cross-sectional boundaries, the impact of the channel length should be taken into consideration during the modeling of thermal conductivity for accurately evaluating the self-heating effects (SHEs) in GAA SiNW FETs.

Efficiency enhancement of an ultra-thin film silicon solar cell using conical-shaped nanoparticles: similar to superposition (top, middle, and bottom)

The use of conical-shaped plasmonic nanostructures for light management in an ultra-thin silicon solar cell has been investigated. The optical absorption and hence photocurrent are obtained for several cases of structures using finite difference time domain simulations. In this paper, we demonstrate that the use of superposition theorem causes significant photocurrent enhancement due to the surface plasmonic effects of nanoparticles. For this, at first, we used one conical-shaped nanoparticle at the top side, then in the rear side, and finally, three nanoparticles are used in the top, bottom, and middle sides. Depending on the incident light wavelength, each nanoparticle manipulates the part of the spectrum. The photocurrents of 9.165, 10.463, 16.402, 17.761, and 18.072 mA/cm2, are obtained for a cell without nanoparticles, with one conical-shaped NP at the top, with one conical-shaped NP at the bottom, with two NPs at top and bottom and with three NPs at the top, bottom, and middle, respectively. Finally, the electrical field distribution and generation rate are calculated for proposed structures.

Observation of energy transfer at optical frequency to an ultrathin silicon waveguide.

Energy transfer from a submonolayer of rhodamine 6G molecules to a 130 nm thick crystalline silicon (Si) waveguide is investigated. The dependence of the fluorescence lifetime of rhodamine on its distance to the Si waveguide is characterized and modeled successfully by a classical dipole model. The energy transfer process could be regarded as photon tunneling into the Si waveguide via the evanescent waves. The experimentally observed tunneling rate is well described by an analytical expression obtained via a complex variable analysis in the complex wavenumber plane.

Surface kinetics and feature scale particle model of SixNy atomic layer deposition using Si2Cl6 precursor

One of the important steps in the fabrication of semiconductor memory devices is the deposition of ultrathin silicon nitride films with uniform film thickness and electrical properties. Such high-quality films have made atomic level control during deposition a necessity and can be achieved via atomic layer deposition (ALD) with excellent step coverage. While ALD has been studied experimentally by many authors, there exist significant gaps between their observations and the practical application of the ALD process in large-scale manufacturing. In this work, a computational model of thin film deposition for a silicon based ALD application was developed. The model includes a surface chemistry mechanism for the deposition of hexachlorodisilane (Si2Cl6) on a growing SixNy film. This mechanism quantifies the sticking probability of the Si2Cl6 precursor on the growth surface as well as an effective active reaction site density on these surfaces. This surface reaction chemistry was used in the context of a feature scale particle transport model to simulate ALD in 100 nm–1 μm critical dimension, ∼10–100 high aspect ratio holes. The model demonstrates the effects of hole size and aspect ratio dependence on the overall kinetics of the deposition process. An increase in the completion time for ALD processes with increasing hole aspect ratio and the increasing statistical nature of the deposition process with smaller critical dimension of the hole were predicted.

Critical flux behavior of ultrathin membranes in protein-rich solutions

Critical flux defines the ideal operating conditions in tangential flow filtration (TFF). Below this value a TFF process can, in principle, proceed indefinitely without membrane fouling. The critical flux behavior of ultrathin membranes, which are particularly valuable for small volume processing, has not yet been explored. Here we investigate the critical flux behavior of ultrathin nanoporous silicon nitride (NPN) membranes in concentrated protein solutions using a microfluidic TFF device. We find that NPN (~19% porosity; 60 nm average pore size; 100 nm thick) has the ability to process bovine serum albumin (BSA) solutions as concentrated as 10 mg/mL at 30 μL/min without exceeding a critical flux threshold. At 30 mg/mL and 60 mg/mL, NPN enables 40% and 20% of the supply to be filtered without fouling. In these experiments, NPN membranes achieve critical flux values as high as ~1200 LMH, which is 5x larger than 0.2 μm polyethersulfone (PES) membranes processing 5 mg/mL BSA and an order of magnitude higher than track-etch polymeric membranes (10 μm thick; 80 nm pores) in direct comparisons. The effects of nanoparticle capture on critical flux are also studied here, simulating the capture of small extracellular vesicles (sEVs) in forthcoming diagnostic applications. Our work not only demonstrates the utility of ultrathin membranes for processing concentrated protein solutions, it illustrates the value of applying membrane science principles developed for macroscale systems (e.g. critical flux, TFF) to the micro/nano scale.

Performance Evaluation and Device Physics Investigation of Negative-Capacitance MOSFETs Based on Ultrathin Body Silicon and Monolayer MoS2

The proposition of integrating the 2-D materials and ferroelectric negative-capacitance MOSFETs (NCFETs) was expected to have excellent steep slope ${I}$ – ${V}$ characteristics due to the combined advantages of both ultrathin body channel material and negative-capacitance effect. Recent experiments demonstrated the excellent steep slope features of 2-D material NCFETs. Therefore, it was important to understand the device physics of this characteristic, its performance projection, and the benchmark with NCFETs based on conventional Group IV materials. In this article, we conducted a computational study of 2-D material NCFETs based on MoS2 under the nonequilibrium Green’s function (NEGF)-Poisson self-consistent scheme with free-Gibbs energy calculation to judge the operating path in polarization–electric field (P–E) relation. Monolayer MoS2 (1L-MoS2) was chosen as channel material while various thickness of ultrathin body silicon (UTB-Si) for benchmark purpose. The results showed an excellent average subthreshold slope (SS) of ~25 mV/dec in 1L-MoS2 NCFETs compared to ~32 mV/dec of the UTB-Si counterparts. It was found that the steep-slope features in 1L-MoS2 NCFETs could be attributed to the more optimized capacitance matching in 1L-MoS2 NCFETs and tunneling currents at the subthreshold region.

Sub-surface Damage of Ultra-Thin Monocrystalline Silicon Wafer Induced by Dry Polishing

Ultra-thin wafer fabrication has become a hot spot in recent years with the growing demand for small size and high performance electronic devices. However, far less research focused on the damage behavior in ultra-thin wafer. In this work, 300 mm diameter silicon wafer was thinned to 6 µm thick by grinding plus ultra-precision dry polishing. The damage behavior before and after the dry polishing was discussed. Mechanical and surface analysis showed that the dry polishing process can help improve the strength and surface uniformity of ultra-thin wafer by removing high pressure phase and micro cracks. Series of nano beam diffraction patterns revealed the stress induced by the thinning process only existed in surface. High resolution transmission electron microscopy images analyzed by geometric phase approach indicated that surface dislocations can move across the wafer and reached bottom device layers during the dry polishing, increasing the risk of electrical deterioration. The findings are of great significance to the study on process optimization of ultra-thin wafer and provide insights into the reliability of advanced electronic packaging.

Ultrathin Silicon Nanowires Produced by a Bi-Metal-Assisted Chemical Etching Method for Highly Stable Lithium-Ion Battery Anodes

Silicon is widely studied as a high-capacity lithium-ion battery anode. However, the pulverization of silicon caused by a large volume expansion during lithiation impedes it from being used as a next generation anode for lithium-ion batteries. To overcome this drawback, we synthesized ultrathin silicon nanowires. These nanowires are 1D silicon nanostructures fabricated by a new bi-metal-assisted chemical etching process. We compared the lithium-ion battery properties of silicon nanowires with different average diameters of 100[Formula: see text]nm, 30[Formula: see text]nm and 10[Formula: see text]nm and found that the 30[Formula: see text]nm ultrathin silicon nanowire anode has the most stable properties for use in lithium-ion batteries. The above anode demonstrates a discharge capacity of 1066.0[Formula: see text]mAh/g at a current density of 300[Formula: see text]mA/g when based on the mass of active materials; furthermore, the ultrathin silicon nanowire with average diameter of 30[Formula: see text]nm anode retains 87.5% of its capacity after the 50th cycle, which is the best among the three silicon nanowire anodes. The 30[Formula: see text]nm ultrathin silicon nanowire anode has a more proper average diameter and more efficient content of SiOx. The above prevents the 30[Formula: see text]nm ultrathin silicon nanowires from pulverization and broken during cycling, and helps the 30[Formula: see text]nm ultrathin silicon nanowires anode to have a stable SEI layer, which contributes to its high stability.