Showing papers on "Silicon published in 2019"

Graphene and two-dimensional materials for silicon technology.

Abstract: The development of silicon semiconductor technology has produced breakthroughs in electronics—from the microprocessor in the late 1960s to early 1970s, to automation, computers and smartphones—by downscaling the physical size of devices and wires to the nanometre regime. Now, graphene and related two-dimensional (2D) materials offer prospects of unprecedented advances in device performance at the atomic limit, and a synergistic combination of 2D materials with silicon chips promises a heterogeneous platform to deliver massively enhanced potential based on silicon technology. Integration is achieved via three-dimensional monolithic construction of multifunctional high-rise 2D silicon chips, enabling enhanced performance by exploiting the vertical direction and the functional diversification of the silicon platform for applications in opto-electronics and sensing. Here we review the opportunities, progress and challenges of integrating atomically thin materials with silicon-based nanosystems, and also consider the prospects for computational and non-computational applications. Progress in integrating atomically thin two-dimensional materials with silicon-based technology is reviewed, together with the associated opportunities and challenges, and a roadmap for future applications is presented.

Silicon oxides: a promising family of anode materials for lithium-ion batteries

Abstract: Silicon oxides have been recognized as a promising family of anode materials for high-energy lithium-ion batteries (LIBs) owing to their abundant reserve, low cost, environmental friendliness, easy synthesis, and high theoretical capacity. However, the extended application of silicon oxides is severely hampered by the intrinsically low conductivity, large volume change, and low initial coulombic efficiency. Significant efforts have been dedicated to tackling these challenges towards practical applications. This Review focuses on the recent advances in the synthesis and lithium storage properties of silicon oxide-based anode materials. To present the progress in a systematic manner, this review is categorized as follows: (i) SiO-based anode materials, (ii) SiO2-based anode materials, (iii) non-stoichiometric SiOx-based anode materials, and (iv) Si-O-C-based anode materials. Finally, future outlook and our personal perspectives on silicon oxide-based anode materials are presented.

Scalable synthesis of ant-nest-like bulk porous silicon for high-performance lithium-ion battery anodes

Abstract: Although silicon is a promising anode material for lithium-ion batteries, scalable synthesis of silicon anodes with good cyclability and low electrode swelling remains a significant challenge. Herein, we report a scalable top-down technique to produce ant-nest-like porous silicon from magnesium-silicon alloy. The ant-nest-like porous silicon comprising three-dimensional interconnected silicon nanoligaments and bicontinuous nanopores can prevent pulverization and accommodate volume expansion during cycling resulting in negligible particle-level outward expansion. The carbon-coated porous silicon anode delivers a high capacity of 1,271 mAh g−1 at 2,100 mA g−1 with 90% capacity retention after 1,000 cycles and has a low electrode swelling of 17.8% at a high areal capacity of 5.1 mAh cm−2. The full cell with the prelithiated silicon anode and Li(Ni1/3Co1/3Mn1/3)O2 cathode boasts a high energy density of 502 Wh Kg−1 and 84% capacity retention after 400 cycles. This work provides insights into the rational design of alloy anodes for high-energy batteries. Silicon is a promising anode material for lithium-ion batteries but experiences large volume changes during cycling. Here the authors report a scalable method to synthesize porous ant-nest-like silicons. The unique structure of this anode solves the swelling problem and enables impressive performance.

Application of silicon nanoparticles in agriculture

Abstract: The beneficial effects of silicon and its role for plants are well established; however, the advantages of silicon nanoparticles over its bulk material are an area that is less explored. Silicon nanoparticles have distinctive physiological characteristics that allow them to enter plants and influence plant metabolic activities. The mesoporous nature of silicon nanoparticles also makes them good candidates as suitable nanocarriers for different molecules that may help in agriculture. Several studies have shown the importance of silicon nanoparticles in agriculture, but an overview of the related aspects was missing. Therefore, this review brings together the literature on silicon nanoparticles and discusses the impact of silicon nanoparticles on several aspects of agricultural sciences. The review also discusses the future application of silicon nanoparticles in plant growth, plant development, and improvement of plant productivity.

Large Pockels effect in micro- and nanostructured barium titanate integrated on silicon

Abstract: The electro-optical Pockels effect is an essential nonlinear effect used in many applications. The ultrafast modulation of the refractive index is, for example, crucial to optical modulators in photonic circuits. Silicon has emerged as a platform for integrating such compact circuits, but a strong Pockels effect is not available on silicon platforms. Here, we demonstrate a large electro-optical response in silicon photonic devices using barium titanate. We verify the Pockels effect to be the physical origin of the response, with r42 = 923 pm V−1, by confirming key signatures of the Pockels effect in ferroelectrics: the electro-optic response exhibits a crystalline anisotropy, remains strong at high frequencies, and shows hysteresis on changing the electric field. We prove that the Pockels effect remains strong even in nanoscale devices, and show as a practical example data modulation up to 50 Gbit s−1. We foresee that our work will enable novel device concepts with an application area largely extending beyond communication technologies. Electro-optic modulators based on epitaxial barium titanate (BTO) integrated on silicon exhibit speeds up to 50 Gbit s–1 while the Pockels coefficient of the BTO film is found to be approaching the bulk value.

Nano/Microstructured Silicon–Graphite Composite Anode for High-Energy-Density Li-Ion Battery

Abstract: With the ever-increasing demand for lithium-ion batteries (LIBs) with higher energy density, tremendous attention has been paid to design various silicon-active materials as alternative electrodes due to their high theoretical capacity (ca. 3579 mAh g–1). However, totally replacing the commercially utilized graphite with silicon is still insurmountable owing to bottlenecks such as low electrode loading and insufficient areal capacity. Thus, in this study, we turn back to enhanced graphite electrode through the cooperation of modified silicon via a facile and scalable blending process. The modified nano/microstructured silicon with boron doping and carbon nanotube wedging (B–Si/CNT) can provide improved stability (88.2% retention after 200 cycles at 2000 mA g–1) and high reversible capacity (∼2426 mAh g–1), whereas the graphite can act as a tough framework for high loading. Owing to the synergistic effect, the resultant B–Si/CNT–graphite composite (B–Si/CNT@G) shows a high areal capacity of 5.2 mAh cm–2 an...

Micro optical sensors based on avalanching silicon light-emitting devices monolithically integrated on chips

Abstract: Silicon avalanche light-emitting devices (Si Av LEDs) offer various possibilities for realizing micro- and even nano- optical biosensors directly on chip. The light-emitting devices (LEDs) operate in the wavelength range of about 450-850nm, and their optical power emitted is of the order of a few hundreds of nW/µm2. These LEDs could be fabricated in micro- and nano- dimensions by using modern semiconductor fabrication processing technologies through the mainstream of silicon material. Through a series of experiments, the dispersion phenomena in the Si Av LED are observed. Also, its light emission point was proved to locate at about one micron just below the silicon-silicon oxide interface. Subsequently, a micro-fluidic channel sensor was designed by using the dispersion characteristics owned by the Si Av LED. The analytes flowing through a micro-fluidic channel could be studied by their specific transmittance and absorption spectra. Moreover, simulations verify that a novel designed waveguide-based sensor could be fabricated on chip between the Si optical source and the Si P-I-N detector.

Infrared Light Management Using a Nanocrystalline Silicon Oxide Interlayer in Monolithic Perovskite/Silicon Heterojunction Tandem Solar Cells with Efficiency above 25%

Abstract: Perovskite/silicon tandem solar cells are attractive for their potential for boosting cell efficiency beyond the crystalline silicon (Si) single-junction limit. However, the relatively large optical refractive index of Si, in comparison to that of transparent conducting oxides and perovskite absorber layers, results in significant reflection losses at the internal junction between the cells in monolithic (two-terminal) devices. Therefore, light management is crucial to improve photocurrent absorption in the Si bottom cell. Here it is shown that the infrared reflection losses in tandem cells processed on a flat silicon substrate can be significantly reduced by using an optical interlayer consisting of nanocrystalline silicon oxide. It is demonstrated that 110 nm thick interlayers with a refractive index of 2.6 (at 800 nm) result in 1.4 mA cm − ² current gain in the silicon bottom cell. Under AM1.5G irradiation, the champion 1 cm 2 perovskite/silicon monolithic tandem cell exhibits a top cell + bottom cell total current density of 38.7 mA cm −2 and a certified stabilized power conversion efficiency of 25.2%.

A two-qubit gate between phosphorus donor electrons in silicon

Abstract: Electron spin qubits formed by atoms in silicon have large (tens of millielectronvolts) orbital energies and weak spin–orbit coupling, giving rise to isolated electron spin ground states with coherence times of seconds1,2. High-fidelity (more than 99.9 per cent) coherent control of such qubits has been demonstrated3, promising an attractive platform for quantum computing. However, inter-qubit coupling—which is essential for realizing large-scale circuits in atom-based qubits—has not yet been achieved. Exchange interactions between electron spins4,5 promise fast (gigahertz) gate operations with two-qubit gates, as recently demonstrated in gate-defined silicon quantum dots6–10. However, creating a tunable exchange interaction between two electrons bound to phosphorus atom qubits has not been possible until now. This is because it is difficult to determine the atomic distance required to turn the exchange interaction on and off while aligning the atomic circuitry for high-fidelity, independent spin readout. Here we report a fast (about 800 picoseconds) $$\sqrt{{\bf{SWAP}}}$$ two-qubit exchange gate between phosphorus donor electron spin qubits in silicon using independent single-shot spin readout with a readout fidelity of about 94 per cent on a complete set of basis states. By engineering qubit placement on the atomic scale, we provide a route to the realization and efficient characterization of multi-qubit quantum circuits based on donor qubits in silicon. A fast, high-fidelity two-qubit exchange gate between phosphorus donor electron spin qubits in silicon is demonstrated by creating a tunable exchange interaction between two electrons bound to phosphorus atom qubits.

Flexible and Freestanding Silicon/MXene Composite Papers for High-Performance Lithium-Ion Batteries.

Abstract: Silicon has been developed as the exceptionally desirable anode candidate for lithium-ion batteries (LIBs), attributing to its highest theoretical capacity, low working potential, and abundant resource. However, large volume expansion and poor conductivity hinder its practical application. Herein, we fabricate flexible, freestanding, and binder-free silicon/MXene composite papers directly as anodes for LIBs. The Silicon/MXene composite papers are synthesized via covalently anchoring silicon nanospheres on the highly conductive networks based on MXene sheets by vacuum filtration. This unique architecture can accommodate large volume expansion, enhance conductivity of composites, prevent restacking of MXene sheets, offer additional active sites, and facilitate efficient ion transport, which exhibits superior electrochemical performance with a high capacity of 2118 mAh·g–1 at 200 mA·g–1 current density after 100 cycles, a steady cycling ability of 1672 mAh·g–1 at 1000 mA·g–1 after 200 cycles, and a rate perf...

High-speed colour-converting photodetector with all-inorganic CsPbBr3 perovskite nanocrystals for ultraviolet light communication

Abstract: Optical wireless communication (OWC) using the ultra-broad spectrum of the visible-to-ultraviolet (UV) wavelength region remains a vital field of research for mitigating the saturated bandwidth of radio-frequency (RF) communication. However, the lack of an efficient UV photodetection methodology hinders the development of UV-based communication. The key technological impediment is related to the low UV-photon absorption in existing silicon photodetectors, which offer low-cost and mature platforms. To address this technology gap, we report a hybrid Si-based photodetection scheme by incorporating CsPbBr3 perovskite nanocrystals (NCs) with a high photoluminescence quantum yield (PLQY) and a fast photoluminescence (PL) decay time as a UV-to-visible colour-converting layer for high-speed solar-blind UV communication. The facile formation of drop-cast CsPbBr3 perovskite NCs leads to a high PLQY of up to ~73% and strong absorption in the UV region. With the addition of the NC layer, a nearly threefold improvement in the responsivity and an increase of ~25% in the external quantum efficiency (EQE) of the solar-blind region compared to a commercial silicon-based photodetector were observed. Moreover, time-resolved photoluminescence measurements demonstrated a decay time of 4.5 ns under a 372-nm UV excitation source, thus elucidating the potential of this layer as a fast colour-converting layer. A high data rate of up to 34 Mbps in solar-blind communication was achieved using the hybrid CsPbBr3–silicon photodetection scheme in conjunction with a 278-nm UVC light-emitting diode (LED). These findings demonstrate the feasibility of an integrated high-speed photoreceiver design of a composition-tuneable perovskite-based phosphor and a low-cost silicon-based photodetector for UV communication. A silicon-based receiver that incorporates perovskite nanocrystals efficiently detects ultraviolet signals, paving the way towards high-speed, high-bandwidth UV wireless communication. The photodetector (PD), developed by Boon S. Ooi of King Abdullah University of Science and Technology (KAUST) and colleagues in Saudi Arabia, is less bulky and cheaper to manufacture than currently available receivers. It builds on technologically advanced silicon-based PDs, which are compact and widely available, but respond best to higher wavelength green light. Incorporating cesium lead bromide (CsPbBr3) perovskite nanocrystals into a silicon-based PD facilitated efficient conversion of UV into green light. The team demonstrated that their receiver could be used in high-speed UV-based communication, paving the way for the use of perovskite-based materials in terrestrial and underwater UV-Internet systems.

Sensitization of silicon by singlet exciton fission in tetracene

Abstract: Silicon dominates contemporary solar cell technologies1. But when absorbing photons, silicon (like other semiconductors) wastes energy in excess of its bandgap2. Reducing these thermalization losses and enabling better sensitivity to light is possible by sensitizing the silicon solar cell using singlet exciton fission, in which two excited states with triplet spin character (triplet excitons) are generated from a photoexcited state of higher energy with singlet spin character (a singlet exciton)3–5. Singlet exciton fission in the molecular semiconductor tetracene is known to generate triplet excitons that are energetically matched to the silicon bandgap6–8. When the triplet excitons are transferred to silicon they create additional electron–hole pairs, promising to increase cell efficiencies from the single-junction limit of 29 per cent to as high as 35 per cent9. Here we reduce the thickness of the protective hafnium oxynitride layer at the surface of a silicon solar cell to just eight angstroms, using electric-field-effect passivation to enable the efficient energy transfer of the triplet excitons formed in the tetracene. The maximum combined yield of the fission in tetracene and the energy transfer to silicon is around 133 per cent, establishing the potential of singlet exciton fission to increase the efficiencies of silicon solar cells and reduce the cost of the energy that they generate. A silicon and tetracene solar cell employing singlet fission uses an eight-angstrom-thick hafnium oxynitride interlayer to promote efficient triplet transfer, increasing the efficiency of the cell.

Highly efficient monolithic perovskite silicon tandem solar cells: analyzing the influence of current mismatch on device performance

Abstract: Metal halide perovskites show great promise to enable highly efficient and low cost tandem solar cells when being combined with silicon. Here, we combine rear junction silicon heterojunction bottom cells with p–i–n perovskite top cells into highly efficient monolithic tandem solar cells with a certified power conversion efficiency (PCE) of 25.0%. Further improvements are reached by reducing the current mismatch of the certified device. The top contact and perovskite thickness optimization allowed increasing the JSC above 19.5 mA cm−2, enabling a remarkable tandem PCE of 26.0%, however with a slightly limited fill factor (FF). To test the dependency of the FF on the current mismatch between the sub-cells, the tandems' J–V curves are measured under various illumination spectra. Interestingly, the reduced JSC in unmatched conditions is partially compensated by an enhancement of the FF. This finding is confirmed by electrical simulations based on input parameters from reference single junction devices. The simulations reveal that especially the FF in the experiment is below the expected value and show that with improved design we could reach 29% PCE for our monolithic perovskite/silicon tandem device and 31% PCE if record perovskite and silicon cell single junctions could be combined in tandem solar cells.

Engineering the Distribution of Carbon in Silicon Oxide Nanospheres at the Atomic Level for Highly Stable Anodes

Abstract: The application of high-performance silicon-based anodes, which are among the most prominent anode materials, is hampered by their poor conductivity and large volume expansion. Coupling of silicon-based anodes with carbonaceous materials is a promising approach to address these issues. However, the distribution of carbon in reported hybrids is normally inhomogeneous and above the nanoscale, which leads to decay of coulombic efficiency during deep galvanostatic cycling. Herein, we report a porous silicon-based nanocomposite anode derived from phenylene-bridged mesoporous organosilicas (PBMOs) through a facile sol-gel method and subsequent pyrolysis. PBMOs show molecularly organic-inorganic hybrid character, and the resulting hybrid anode can inherit this unique structure, with carbon distributed homogeneously in the Si-O-Si framework at the atomic scale. This uniformly dispersed carbon network divides the silicon oxide matrix into numerous sub-nanodomains with outstanding structural integrity and cycling stability.

Silicon/Carbon Composite Anode Materials for Lithium-Ion Batteries

Abstract: Silicon (Si) is a representative anode material for next-generation lithium-ion batteries due to properties such as a high theoretical capacity, suitable working voltage, and high natural abundance. However, due to inherently large volume expansions (~ 400%) during insertion/deinsertion processes as well as poor electrical conductivity and unstable solid electrolyte interfaces (SEI) films, Si-based anodes possess serious stability problems, greatly hindering practical application. To resolve these issues, the modification of Si anodes with carbon (C) is a promising method which has been demonstrated to enhance electrical conductivity and material plasticity. In this review, recent researches into Si/C anodes are grouped into categories based on the structural dimension of Si materials, including nanoparticles, nanowires and nanotubes, nanosheets, and porous Si-based materials, and the structural and electrochemical performance of various Si/C composites based on carbon materials with varying structures will be discussed. In addition, the progress and limitations of the design of existing Si/C composite anodes are summarized, and future research perspectives in this field are presented.

High-fidelity spin and optical control of single silicon-vacancy centres in silicon carbide

Abstract: Scalable quantum networking requires quantum systems with quantum processing capabilities. Solid state spin systems with reliable spin–optical interfaces are a leading hardware in this regard. However, available systems suffer from large electron–phonon interaction or fast spin dephasing. Here, we demonstrate that the negatively charged silicon-vacancy centre in silicon carbide is immune to both drawbacks. Thanks to its 4A2 symmetry in ground and excited states, optical resonances are stable with near-Fourier-transform-limited linewidths, allowing exploitation of the spin selectivity of the optical transitions. In combination with millisecond-long spin coherence times originating from the high-purity crystal, we demonstrate high-fidelity optical initialization and coherent spin control, which we exploit to show coherent coupling to single nuclear spins with ∼1 kHz resolution. The summary of our findings makes this defect a prime candidate for realising memory-assisted quantum network applications using semiconductor-based spin-to-photon interfaces and coherently coupled nuclear spins. Point defects in solids have potential applications in quantum technologies, but the mechanisms underlying different defects’ performance are not fully established. Nagy et al. show how the wavefunction symmetry of silicon vacancies in SiC leads to promising optical and spin coherence properties.

Ultrasensitive 2D Bi2O2Se Phototransistors on Silicon Substrates

Abstract: 2D materials are considered as intriguing building blocks for next-generation optoelectronic devices. However, their photoresponse performance still needs to be improved for practical applications. Here, ultrasensitive 2D phototransistors are reported employing chemical vapor deposition (CVD)-grown 2D Bi2 O2 Se transferred onto silicon substrates with a noncorrosive transfer method. The as-transferred Bi2 O2 Se preserves high quality in contrast to the serious quality degradation in hydrofluoric-acid-assisted transfer. The phototransistors show a responsivity of 3.5 × 104 A W-1 , a photoconductive gain of more than 104 , and a time response in the order of sub-millisecond. With back gating of the silicon substrate, the dark current can be reduced to several pA. This yields an ultrahigh sensitivity with a specific detectivity of 9.0 × 1013 Jones, which is one of the highest values among 2D material photodetectors and two orders of magnitude higher than that of other CVD-grown 2D materials. The high performance of the phototransistor shown here together with the developed unique transfer technique are promising for the development of novel 2D-material-based optoelectronic applications as well as integrating with state-of-the-art silicon photonic and electronic technologies.

Towards integrated tunable all-silicon free-electron light sources.

Abstract: Extracting light from silicon is a longstanding challenge in modern engineering and physics. While silicon has underpinned the past 70 years of electronics advancement, a facile tunable and efficient silicon-based light source remains elusive. Here, we experimentally demonstrate the generation of tunable radiation from a one-dimensional, all-silicon nanograting. Light is generated by the spontaneous emission from the interaction of these nanogratings with low-energy free electrons (2–20 keV) and is recorded in the wavelength range of 800–1600 nm, which includes the silicon transparency window. Tunable free-electron-based light generation from nanoscale silicon gratings with efficiencies approaching those from metallic gratings is demonstrated. We theoretically investigate the feasibility of a scalable, compact, all-silicon tunable light source comprised of a silicon Field Emitter Array integrated with a silicon nanograting that emits at telecommunication wavelengths. Our results reveal the prospects of a CMOS-compatible electrically-pumped silicon light source for possible applications in the mid-infrared and telecommunication wavelengths. Extracting light from silicon is a longstanding challenge. Here, the authors report an experimental demonstration of free-electron-driven light emission from silicon nanogratings and investigates the feasibility of a compact, all-silicon tunable light source integrated with a silicon field emitter array.

Erbium-doped chalcogenide glass thin film on silicon using femtosecond pulsed laser with different deposition temperatures

Abstract: The properties of Er3+-doped gallium lanthanum sulphide thin films prepared on a silicon substrate by femtosecond pulsed laser deposition were studied as a function of process temperature. The films were characterised using transition electron microscopy imaging, X-ray diffractometry, Raman spectroscopy, fluorescence spectroscopy, and UV–Vis–NIR spectroscopy. The results show that by increasing the substrate temperature, the deposited layer thickness increases and the crystallinity of the films changes. The room temperature photoluminescence and lifetimes of the 4I13/2→4I15/2 transition of Er3+ are reported in the paper.

Scalable and Physical Synthesis of 2D Silicon from Bulk Layered Alloy for Lithium-Ion Batteries and Lithium Metal Batteries.

Abstract: Owing to its distinctive structure and properties, 2D silicon (2DSi) has been widely applied in hydrogen storage, sensors, electronic device, catalysis, electrochemical energy storage, etc. However...

25.1%-Efficient Monolithic Perovskite/Silicon Tandem Solar Cell Based on a p-type Monocrystalline Textured Silicon Wafer and High-Temperature Passivating Contacts

Abstract: A monolithic two-terminal perovskite/silicon tandem solar cell based on an industrial, high-temperature tolerant p-type crystalline silicon bottom cell with a steady-state power conversion efficiency of 25.1% is demonstrated.