Papers by Keyword: Silicon Nanowire

Abstract: This paper presents a novel and effective characterization method for giant piezoresistive properties of silicon nanowires by using the reference structures. This contrast detection approach investigates the influences of quantum size effect and surface defects effect on piezoresistive coefficients of silicon nanowires by direct comparison of the resistivity change ratio of silicon wires with nanoscale-to-microscale width under the same applied stress conditions. The characterization experiments based on four-point bending tensile test demonstrate that piezoresistive coefficient of small nanowidth silicon nanowire can be significantly increased to about five times higher levels than that of bulk silicon under the same impurity concentration, which indicates that the silicon nanowire can have giant piezoresistive effect. On the other hand, to solve the problem on nanowires pick-up, we proposed a nanowire piezoresistive detection approach, whose validity is confirmed by the dynamic LDV resonance test. Meanwhile, to investigate the influence of undercut arising from the wet chemical release process of the suspended silicon nanowire, a three-dimensional finite element simulation is also carried out for the fundamental resonant frequency using ANSYS software. The numerical and experimental results show that our piezoresistive detection is accurate and effective and the undercut should be carefully considered in the design of the high frequency resonator and mixer. The findings of this paper provide some useful references for the piezoresistive effect measurement and the piezoresistive pick-up in nanoelectromechanical system.

Abstract: In this article, impact of cross-section and size on vibration of silicon nanowires is simulated by the molecular dynamics method based on molecular dynamics software Material Studio. The comparison of fundamental frequencies of the silicon nanowires with triangle, diamond, and hexagon cross sections is carried out. The orientations of these silicon nanowires are all in <111> direction. Then we change the length and the width of silicon nanowires to investigate the impact of size on vibration of silicon nanowires. The results show that with the influence of surface effect, the vibration frequency of silicon nanowires strongly depends on cross-section and size.

Abstract: A top-down silicon nanowire fabrication using a combination of optical lithography and orientation dependent etching (ODE) has been developed using <100> Silicon-on Insulator (SOI) as the starting substrate. Initially, the samples were doped with phosphorus using the diffusion process resulting in carrier concentration of 2 x 10¹⁸ cm^-3. After the silicon nanowires were fabricated, they were measured using a dual configuration method which is similar to the four-point probe measurement technique to deduce its resistivity. The data obtained had suggested that doping distribution in the silicon nanowires were lower and this may have been affected by the surface depletion effect. In addition, with respect to carrier mobility, the effective mobility of electrons extracted using the four-point probe data had demonstrated that the mobility of carriers in the silicon nanowire is comparable with the bulk mobility. This is most probably due to the fact that in this research, the quantum confinement effect on these nanowires is not significant.

Abstract: Silicon film as a surface passivation layer is reported to reduce surface recombination on silicon nanowires (SiNWs) and thus enable to improve SiNW solar cell (SC) performance. A question yet to be answered regards the link between the silicon film assets and the solar cell performances. We investigated the effect of the properties of silicon films on the SiNWs SC performances by adjusting hydrogen dilution. Our results showed that the open-circuit voltage (Voc) and short-circuit current density (Jsc) of SiNWs SC increase until hydrogen dilution 10 and then decrease. An open-circuit voltage of 0.397 V and short-circuit current density of 18.42 mA/cm2 are achieved at optimized hydrogen dilution. Based on the analysis of silicon film properties we proposed that the increase of defect density with hydrogen dilution was the main cause for the deterioration of SiNWs SC performance.

Abstract: In this paper, we propose a new type of optical waveguide called silicon nanowire embedded equai-angular spiral photonic crystal fiber (SN-SPCF) using fully vectorial finite element method, where closely arranged arrays of air holes act as cladding and nanosize silicon material at the centre acts as core. We show that the proposed nanowire embedded PCF of 400 nm core diameter exhibits high anomalous group velocity dispersion (-3148 ps²/km), small third order dispersion (-8.6591 ps³/km) and high nonlinearity (443.2 W^-1m^-1) at 1550 nm wavelength. Soliton-effect pulse compression of femtosecond pulses in a silicon nanowire-spiral photonic crystal fiber at 1550 nm is numerically studied. We demonstrate a pulse compression of 75 fs input pulse to about 4 fs by the simultaneous actions of both linear effects (a large anomalous group velocity dispersion and a small third order dispersion) and the nonlinear effect (an effective high nonlinearity).

Abstract: Silicon nanowires (SiNWs) are important candidate for high performance electronic and optoelectronic devices due to their unique structures, electrical and optical properties. SiNWs were fabricated by silver-assisted electroless etching of Si wafer. Vertically aligned SiNW arrays with length about 8.75 μm and diameter of less than 90 nm have been fabricated. The reflectance of SiNWs without dye (12%) is greatly lower compared to bare Si wafer (25%). Therefore, SiNWs on Si substrate can be used as a good anti-reflection layer for a wide range of incident light. The reflectance of dye-sensitized SiNWs with red, green and blue dyes is 7%, 5.5%, and 5% respectively. The results confirmed that the reflectance of SiNWs with dye is much lower compared to SiNWs without dye and bare Si wafer. It was proven that dye on SiNWs can be used to reduce the reflectance (improved absorption) about 40% compared to SiNWs without dye.

Abstract: In this paper, a single silicon nanoemitter were investigated by means of experiments and simulation models andthe emitters array was fabricated by dry etching using an inductively coupled plasma (ICP) through a three-step process. Besides, in order to understand the field emission phenomenon in nano/micro scale, a novel experimental measurement technique by SEM with nanomotors including the constant voltage and the constant emission modes was developed to measure the accurate field emission properties.The results indicated that etching method is a good way to make the uniform field emitters and the electron field emission from a single nanoemitter is a barrier tunneling, quantum mechanicalprocess.

Abstract: In this work, we report the used of Negative Pattern Scheme (NPS) by Electron Microscope Based Electron Beam Lithography (EBL) Technique in connection with scanning electron microscope (SEM) for creating extremely fine nanowires. These patterns have been designed using GDSII Editor and directly transferred on the sample coated with ma-N 2400 Series as the negative tone e-beam resist. The NPS designs having line width of approximately 100 nm are successfully fabricated at our lab. The profile of the nanowire can be precisely controlled by this technique. The optical characterization that is applied to check the nanowires structure using SEM and Atomic Force Microscopy (AFM).

Abstract: A simple method for the fabrication of silicon nanowires using Electron Beam Lithography (EBL) combined with thermal oxidation size reduction method is presented. EBL is used to define the initial silicon nanowires of dimensions approximately 100 nm. Size-reduction method is employed for reaching true nanoscale of dimensions approximately 20 nm. Dry oxidation of silicon is well investigated process for self-limited size-reduction of silicon nanowires. In this paper, successful size reduction of silicon nanowires is presented and surface topography characterizations using Atomic Force Microscopy (AFM) are reported.

Abstract: One-step metal-assisted electroless chemical etching of p-type silicon substrate in NH₄HF₂/AgNO₃ solution was investigated. The effect of different etching parameters including etching time, temperature, AgNO₃ concentration and NH₄HF₂ concentration were investigated. The etched layers formed were investigated by scanning electron microscopy (SEM) and Photoluminescence. It was found that the etched layer was formed by well-aligned silicon nanowires. It is noted that their density and length strongly depend on etching parameters. Room temperature photoluminescence (PL) from etched layer was observed. It was observed that PL peak intensity increases significantly with AgNO₃ concentration.