基于湿法腐蚀工艺的高性能黑硅光电探测器

采用基于硝酸/氢氟酸/磷酸/硫酸混合液的湿法腐蚀工艺,实现了高吸收效率的黑硅结构的制备与工艺集成,获得了具有近红外响应增强效果的黑硅PIN光电探测器,并与未集成黑硅的PIN光电探测器的性能参数进行了对比测试.测试结果显示,黑硅光电探测器在1 060 nm波长下的响应度达到0.69 A/W(量子效率80.7％),较未集成黑硅的器件提高了 116％;黑硅探测器暗电流小于8 nA,响应时间小于8 ns,电容小于9 pF,与未集成黑硅的器件相当.得益于工艺兼容性,所采用的黑硅技术具有广泛应用于硅基近红外PIN,APD,SPAD,SPM等光电探测器的潜力,可显著提高器件的响应率、量子效率、响应速度、击穿电压温度系数等性能.     

Direct Growth of Nanographene on Silicon with Thin Oxide Layer for High‐Performance Nanographene‐Oxide‐Silicon Diodes

Graphene‐silicon based configurations are attracting great attention for their potential application as electronics and optoelectronics. For their practical use, it is still limited by the configuration fabrication process. In this paper, a catalyst‐free method is reported to directly grow nanographene on silicon covered with a thin oxide layer to form nanographene‐oxide‐silicon configurations. Compared with previously reported nanographene‐silicon Schottky junctions, the nanographene‐oxide‐silicon structures exhibit a high performance on electronic and photovoltaic properties. The reverse leakage current of the nanographene‐oxide‐silicon is suppressed from over 10^?5 A down to 10^?8 A and the rectifier ratio is greatly enhanced from less than 5 up to 10³. The photovoltage is enhanced over 50 times. The nanographene‐oxide‐silicon structures exhibit especially ultrasensitive to weak light at a photovoltage working mode, which exceeds up to 10⁶ V/W at the light power of 0.025 μW. Due to the source material for nanographene is photoresist and the fabrication process is mainly based on the current‐used photolithography and silicon technique, the developed nanographene‐oxide‐silicon structures are very easy for device fabrication, integration, and miniaturization, and could be a promising way to produce metal‐free graphene‐silicon based electronics and optoelectronics for commercial use.     

Effective Silicon Oxide Formation on Silica‐on‐Silicon Platforms for Optical Hybrid Integration

This paper describes an effective method for forming silicon oxide on silica‐on‐silicon platforms, which results in excellent characteristics for hybrid integration. Among the many processes involved in fabricating silica‐on‐silicon platforms with planar lightwave circuits (PLCs), the process for forming silicon oxide on an etched silicon substrate is very important for obtaining transparent silica film because it determines the compatibility at the interface between the silicon and the silica film. To investigate the effects of the formation process of the silicon oxide on the characteristics of the silica PLC platform, we compared two silicon oxide formation processes: thermal oxidation and plasma‐enhanced chemical vapor deposition (PECVD). Thermal oxidation in fabricating silica platforms generates defects and a cristobalite crystal phase, which results in deterioration of the optical waveguide characteristics. On the other hand, a silica platform with the silicon oxide layer deposited by PECVD has a transparent planar optical waveguide because the crystal growth of the silica has been suppressed. We confirm that the PECVD method is an effective process for silicon oxide formation for a silica platform with excellent characteristics.     

Chemical Coupling of Carbon Nanotubes and Silicon Nanoparticles for Improved Negative Electrode Performance in Lithium‐Ion Batteries

Multi‐walled carbon nanotube (MWCNT)/silicon nanocomposites obtained by a grafting technique using the diazonium chemistry are used to prepare silicon negative electrodes for lithium‐ion batteries. The covalent bonding of the two compounds is obtained via mono‐ and multi‐layers of phenyl bridges, leading to an ideal dispersion of MWCNTs and silicon nanoparticles that are bound together. The presence of MWCNTs close to silicon nanoparticles enhances the electronic pathway to the active material particles and probably helps to prevent silicon decrepitation upon repeated lithium insertion/extraction by improving the mechanical stability of the electrode at a nanoscale level. This effect results in the enhancement of cycling ability and capacity, which are demonstrated by comparing the nanocomposite electrode to a simple mixture of the two compounds. This technique can be applied to other carbon conductive additives together with silicon or other nanosized active compounds.     

Metal‐Free Growth of Nanographene on Silicon Oxides for Transparent Conducting Applications

Conventional methods to prepare large‐area graphene for transparent conducting electrodes involve the wet etching of the metal catalyst and the transfer of the graphene film, which can degrade the film through the creation of wrinkles, cracks, or tears. The resulting films may also be obscured by residual metal impurities and polymer contaminants. Here, it is shown that direct growth of large‐area flat nanographene films on silica can be achieved at low temperature (400 °C) by chemical vapor deposition without the use of metal catalysts. Raman spectroscopy and TEM confirm the formation of a hexagonal atomic network of sp²‐bonded carbon with a domain size of about 3–5 nm. Further spectroscopic analysis reveals the formation of SiC between the nanographene and SiO₂, indicating that SiC acts as a catalyst. The optical transmittance of the graphene films is comparable with transferred CVD graphene grown on Cu foils. Despite the fact that the electrical conductivity is an order of magnitude lower than CVD graphene grown on metals, the sheet resistance remains 1–2 orders of magnitude better than well‐reduced graphene oxides.     

Vapor‐Phase Deposition of Monofunctional Alkoxysilanes for Sub‐Nanometer‐Level Biointerfacing on Silicon Oxide Surfaces

Improving the performance and lowering the analyte detection limits of optical and electronic biosensors is essential for advancing wide ranging applications in diagnostics and drug discovery. Most sensing methods require direct linkage of a recognition element and a sensor, which is commonly accomplished through an organic monolayer interface. Alkoxyorganosilanes are typically used to prepare sensor surfaces on dielectric oxides. However, many silanes lead to roughened or thick interfaces that degrade device sensitivity. Here, controlled vapor phase deposition of monoalkoxysilanes is found to lead to monolayers resistant to elevated temperatures and extreme pH conditions. The formation of high density, subnanometer monolayers is demonstrated by ellipsometry, XPS, and AFM. The uniform attachment of these monofunctional silanes to such biosensing platforms as microarrays, field effect devices, and the formation of surface enhanced Raman spectroscopy substrates is demonstrated. The advantages of using this silane deposition protocol for the above technologies are also discussed.     

Growth of Metal–Metal Oxide Nanostructures on Freestanding Graphene Paper for Flexible Biosensors

Flexible biosensors are of considerable current interest for the development of portable point‐of‐care medical products, minimally invasive implantable devices, and compact diagnostic platforms. A new type of flexible electrochemical sensor fabricated by depositing high‐density Pt nanoparticles on freestanding reduced graphene oxide paper (rGOP) carrying MnO₂ nanowire networks is reported. The triple‐component design offers new possibilities to integrate the mechanical and electrical properties of rGOP, the large surface area of MnO₂ networks, and the catalytic activity of well‐dispersed and small‐sized Pt nanoparticles prepared via ultrasonic‐electrodeposition. The sensitivity and selectivity that the flexible electrode demonstrates for nonenzymatic detection of H₂O₂ enables its use for monitoring H₂O₂ secretion by live cells. The strategy of structurally integrating metal, metal oxide, and graphene paper will provide new insight into the design of flexible electrodes for a wide range of applications in biosensing, bioelectronics, and lab‐on‐a‐chip devices.     

Self-Consistent SchrÖdinger–Poisson Simulations on Capacitance–Voltage Characteristics of Silicon Nanowire Gate-All-Around MOS Devices With Experimental Comparisons

We simulate room temperature capacitance-voltage characteristics of silicon (Si) nanowire gate-all-around MOS structures with radius les 10 nm using a self-consistent Schrodinger- Poisson solver in cylindrical coordinates with full treatment of the transverse quantum confinement. In this paper, we compare our simulation results with the latest capacitance measurements on single Si nanowire pMOS and nMOS devices in the subfemtofarad range. We also propose to probe the density-of-states features of the Si channel from the capacitance-voltage characteristics at room temperature measurements using dC/dV dependence and illustrate the idea by employing the latest measurements, our quantum and Medici (Synopsys) simulations, as well as a simplified analytical model.     

GeOx/Reduced Graphene Oxide Composite as an Anode for Li‐Ion Batteries: Enhanced Capacity via Reversible Utilization of Li2O along with Improved Rate Performance

A self‐assembled GeO_x/reduced graphene oxide (GeO_x/RGO) composite, where GeO_x nanoparticles are grown directly on reduced graphene oxide sheets, is synthesized via a facile one‐step reduction approach and studied by X‐ray diffraction, transmission electron microscopy, energy dispersive X‐ray spectroscopy, electron energy loss spectroscopy elemental mapping, and other techniques. Electrochemical evaluation indicates that incorporation of reduced graphene oxide enhances both the rate capability and reversible capacity of GeO_x, with the latter being due to the RGO enabling reversible utilization of Li₂O. The composite delivers a high reversible capacity of 1600 mAh g^?1 at a current density of 100 mA g^?1, and still maintains a capacity of 410 mAh g^?1 at a high current density of 20 A g^?1. Owing to the flexible reduced graphene oxide sheets enwrapping the GeO_x particles, the cycling stability of the composite is also improved significantly. To further demonstrate its feasibility in practical applications, the synthesized GeO_x/RGO composite anode is successfully paired with a high voltage LiNi_0.5Mn_1.5O₄ cathode to form a full cell, which shows good cycling and rate performance.     

Development of a Seedless Floating Growth Process in Solution for Synthesis of Crystalline ZnO Micro/Nanowire Arrays on Graphene: Towards High‐Performance Nanohybrid Ultraviolet Photodetectors

A seedless solution process is developed for controllable growth of crystalline ZnO micro/nanowire arrays directly on single‐layer graphene sheets made in chemical vapor deposition (CVD). In particular, the alignment of the ZnO micro/nanowires correlates well with the density of the wires, which is determined by both the sample configuration in solution and the graphene surface cleaning. With increasing wire density, the ZnO micro/nanowire array alignment may be varied from horizontal to vertical by increasing the physical confinement. Ultraviolet photodetectors based on the vertically aligned ZnO micro/nanowires on graphene show high responsivity of 1.62 A W^?1 per volt, a 500% improvement over epitxial ZnO sensors, a 300% improvement over ZnO nanoparticle sensors, and a 40% improvement over the previous best results for nanowire/graphene hybrid sensors. This seedless, floating growth process could be scaled up for large scale growth of oriented ZnO micro/nanowires on graphene at low costs.     

Characterization of an Oxidized Porous Silicon Layer by Complex Process Using RTO and the Fabrication of CPW‐Type Stubs on an OPSL for RF Application

This paper proposes a 10‐µm thick oxide layer structure that can be used as a substrate for RF circuits. The structure has been fabricated using an anodic reaction and complex oxidation, which is a combined process of low‐temperature thermal oxidation (500 °C, for 1 hr at H₂O/O₂) and a rapid thermal oxidation (RTO) process (1050 °C, for 1 min). The electrical characteristics of the oxidized porous silicon layer (OPSL) were almost the same as those of standard thermal silicon dioxide. The leakage current density through the OPSL of 10 µm was about 10 to 50 nA/cm² in the range of 0 to 50 V. The average value of the breakdown field was about 3.9 MV/cm. From the X‐ray photo‐electron spectroscopy (XPS) analysis, surface and internal oxide films of OPSL prepared by a complex process were confirmed to be completely oxidized. The role of the RTO process was also important for the densification of the porous silicon layer (PSL) oxidized at a lower temperature. The measured working frequency of the coplanar waveguide (CPW) type short stub on an OPSL prepared by the complex oxidation process was 27.5 GHz, and the return loss was 4.2 dB, similar to that of the CPW‐type short stub on an OPSL prepared at a temperature of 1050 °C (1 hr at H2O/O2). Also, the measured working frequency of the CPW‐type open stub on an OPSL prepared by the complex oxidation process was 30.5 GHz, and the return was 15 dB at midband, similar to that of the CPW‐type open stub on an OPSL prepared at a temperature of 1050 °C (1 hr at H₂O/O₂).     

Layer‐By‐Layer Dendritic Growth of Hyperbranched Thin Films for Surface Sol–Gel Syntheses of Conformal,Functional, Nanocrystalline Oxide Coatings on Complex 3D (Bio)silica Templates

Here, a straightforward and general method for the rapid dendritic amplification of accessible surface functional groups on hydroxylated surfaces is described, with focus on its application to 3D biomineral surfaces. Reaction of hydroxyl‐bearing silica surfaces with an aminosilane, followed by alternating exposure to a dipentaerythritol‐derived polyacrylate solution and a polyamine solution, allows the rapid, layer‐by‐layer (LBL) build‐up of hyperbranched polyamine/polyacrylate thin films. Characterization of such LBL‐grown thin films by AFM, ellipsometry, XPS, and contact angle analyses reveals a stepwise and spatially homogeneous increase in film thickness with the number of applied layers. UV–Vis absorption analyses after fluorescein isothiocyanate labeling indicate that significant amine amplification is achieved after the deposition of only 2 layers with saturation achieved after 3–5 layers. Use of this thin‐film surface amplification technique for hydroxyl‐enrichment of biosilica templates facilitates the conformal surface sol–gel deposition of iron oxide that, upon controlled thermal treatment, is converted into a nanocrystalline (～9.5 nm) magnetite (Fe₃O₄) coating. The specific adsorption of arsenic onto such magnetite‐coated frustules from flowing, arsenic‐bearing aqueous solutions is significantly higher than for commercial magnetite nanoparticles (≤50 nm in diameter).