Length Of Silicon Nanowires Research Articles

A Novel Method to Grow Vertically Aligned Silicon Nanowires on Si (111) and Their Optical Absorption

In this study we grew silicon nanowires (SiNWs) on Si (111) substrate by gold‐catalyzed vapor liquid solid (VLS) process using tetrachlorosilane (SiCl4) in a hot‐wall chemical vapor deposition reactor. SiNWs with 150–200 nm diameters were found to grow along the orientations of all 〈111〉 family, including the vertical and the inclined, on Si (111). The effects of various process conditions, including SiCl4 concentration, SiCl4 feeding temperature, H2 annealing, and ramp cooling, on the crystal quality and growth orientation of SiNWs, were studied to optimize the growth conditions. Furthermore, a novel method was developed to reliably grow vertically aligned SiNWs on Si (111) utilizing the principle of liquid phase epitaxy (LPE). A ramp‐cooling process was employed to slowly precipitate the epitaxial Si seeds on Si (111) after H2 annealing at 650°C. Then, after heating in SiCl4/H2 up to 850°C to grow SiNWs, almost 100% vertically aligned SiNWs could be achieved reproducibly. The high degree of vertical alignment of SiNWs is effective in reducing surface reflection of solar light with the reflectance decreasing with increasing the SiNWs length. The vertically aligned SiNWs have good potentials for solar cells and nano devices.

Silicon nanowire/organic hybrid solar cell with efficiency of 8.40%

In this work, we investigate in great detail the silicon nanowire (SiNW)/poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hybrid solar cells (SCs). Because of the light-trapping effect, SiNW/PEDOT:PSS SCs absorb more light than planar Si/PEDOT:PSS SCs. Also, the light absorption increases with the length of the SiNWs. However, the SiNW's length is not the only factor that influences the SCs. Thus the SiNW/PEDOT:PSS SCs with the shortest wire length of 0.37μm have the best performance in terms of the highest power conversion efficiency of 8.40%, the largest short circuit current density of 24.24mAcm−2, and open circuit voltage of 0.532V, compared with the SCs of other wire lengths. The reasons are two-fold. First, long SiNWs tend to aggregate at the top portion, making the infiltration of PEDOT:PSS difficult, so the coverage of PEDOT:PSS on the SiNWs is not complete. Second, the increase of SiNW length greatly reduces the minority-carrier lifetime. Our investigation will help develop SiNW SCs with improved performance.

Effect of Oxidation-Induced Tensile Strain on Gate-All-Around Silicon-Nanowire-Based Single-Electron Transistor Fabricated Using Deep-UV Lithography

We report on the electrical characteristics of gate-all-around silicon nanowires (SiNWs) based single-electron transistors (SETs) operating at room temperature. The SiNWs, fabricated using CMOS compatible conventional KrF lithography, have a diameter of around 3 nm and different lengths ranging from 200 to 500 nm. Coulomb blockade oscillations are found to be dependent on the length of the SiNWs, more prominent for longer than shorter SiNWs. For the shortest device of 200 nm, no oscillation is seen and the ID - VG curve reverts to that of a typical MOSFET. The results are interpreted in terms of the effect of SiNW length on the oxidation-induced tensile strain, and consequently, the tunneling barrier height developed in the wires. The study reveals that the SiNW length is a crucial parameter in the design of SiNW-based SETs.

Effect of Wet Etching Parameter on the Diameter and Length of Silicon Nanowires

A wet etching method for preparing silicon nanowires on silicon substrates at near room temperature is presented. The effect of experiment parameter on the silver nanoparticle forming including concentration of AgNO3, immersing time and solution temperature, and the effect of etching time on the length of silicon nanowires are investigated. It is concluded that solution temperature has more impact to diameter of silicon nanowires than concentration of AgNO3 and immersing time and longer etching time may result in longer silicon nanowires.

Fabrication of Large-Area Silicon Nanowire Arrays Based on Electroless Metal Deposition

Electroless metal deposition is a simple, low-cost and effective method for fabricating silicon nanowire arrays and has been used widely in micro electromechanical industry. In this paper, large-area silicon nanowire arrays are prepared successfully with mixed AgNO3 and HF solution by this method at normal temperature and pressure. It has been proved the best equality of silicon nanowires can be obtained at the concentration ratio of 0.02 mol/l: 5mol/l for AgNO3 and HF and 1h reaction time. The influence of nano metal particles on the growth, the wire diameter, the distribution and the array of silicon nanowires are analyzed. Experimental results show the distribution and wire diameter of silicon nanowires can be controlled effectively by nano metal particles deposited on silicon wafers. The length of silicon nanowires increases with the reaction time and the average growth velocity is predicted to be 0.5～0.7μm/min. The equality of silicon nanowires with nano Au particles is better than those with nano Pt particles. The reaction mechanism of preparing large-area silicon nanowire arrays is analyzed as the result of the deoxidization of silver ion and the removal of the oxidized silicon solution by reacting with HF.

Fabrication of highly ordered silicon pin-in-a-hole nanostructures via chemical etching of nanopatterned polymer masks

We present a new technique to fabricate a highly ordered silicon pin-in-a-hole structure, in which each silicon nanowire is pinned in a hole, by combining polymer sphere arrays induced by Rayleigh instability with chemical etching process. With this process, we were able to create the novel structures that are periodic over very large areas (3 × 3 cm2), where the length of silicon nanowires can be varied by tuning the etching time. A silicon pin-in-a-hole structure was used as the template for preparing polymer nanotubes. And also these structures exhibited a superior anti-reflection property showing specular reflectance of about 0.2%, nearly three orders of magnitude lower than that of a planar silicon wafer.

Fabrication of carbon nanotube/silicon nanowire array heterojunctions and their silicon nanowire length dependent photoresponses

Heterojunction structures were fabricated, which consisted of a double-walled carbon nanotube (DWCNT) thin film coated either on an n-type silicon wafer or an n-type silicon nanowires (SiNW) array with varied lengths. Current–voltage characteristics measured under laser (532nm) irradiation showed that the photoresponse [(light current−dark current)/dark current] of the heterojunctions dramatically depends on the length of SiNWs. Increase in the length of SiNWs led first to increase and then to decrease in the photoresponse of DWCNT/SiNW heterojunction. The heterojunction with a SiNW length of ca. 600nm has the highest the photoresponse value of 10.72.

Room temperature growth of wafer-scale silicon nanowire arrays and their Raman characteristics

We report a simple, inexpensive, and rapid process for large area growth of vertically aligned crystalline silicon nanowires (SiNWs) of diameter 40–200 nm and variable length directly on p-type (100) silicon substrate. The process is based on Ag-induced selective etching of silicon wafers wherein the growth of SiNWs was carried out using the aqueous HF solution containing Ag+ ions at room temperature in a Teflon vessel. Effect of etching time has been investigated to understand the evolution of SiNW arrays. It has been found that the length of SiNWs has a linear dependence on the etching time for small to moderate periods (0–2 h). However, etching rate decreases slowly for long etching times (>2 h). Scanning electron microscopy was used to study the morphology of the SiNW arrays. Structural and compositional analysis was carried out using Raman spectroscopy and high-resolution transmission electron microscopy equipped with energy dispersive X-ray spectroscopy. Orders of magnitude intensity enhancement along with a small downshift and broadening in the first-order Raman peak of SiNW arrays was observed in comparison to the bulk crystalline silicon.

Resistivity measurements of intentionally and unintentionally template-grown doped siliconnanowire arrays

High density, intentionally doped silicon nanowire (SiNW) arrays were fabricated within the pores ofanodic alumina (AAO) templates via gold-catalysed vapour–liquid–solid (VLS) growth using silane(SiH4) as the source gas andtrimethylboron ((CH3)3B,TMB) and phosphine (PH3) as p-type and n-type dopant sources, respectively. The AAO template servesas a support structure for nanowire growth and fabrication of electricalcontacts to the nanowire arrays. Nanowire array resistance was measured asa function of SiNW length for a series of samples prepared with differentdopant/SiH4 inlet gas ratios. A method was developed to extract the SiNW resistivityfrom the measurements of array resistance versus nanowire length. Thenanowire resistivity measured from the arrays decreased with increasingdopant/SiH4 ratio and compared favourably with resistivity data obtained from four-point measurements ofindividual SiNWs grown under identical conditions. Nominally undoped SiNWs grownin the AAO templates were found to be p-type with resistivity in the range of1–3 Ω cm, indicating the presence of unintentional acceptors in the wires. The resistivity of undoped SiNWsgrown under identical conditions but on oxidized (100) Si substrates was much higher, of the orderof 104–105 Ω cm, suggesting that the AAO templates are the source of the acceptor impurities.

Chemical Modification of Si Nanowires for Bioconjugation

One-dimensional nanomaterials, such as nanotubes and nanowires, have been investigated in detail for numerous applications due to their extraordinary optical, mechanical, and electrical properties. In the context of both processing and properties of nanowires (NWs), a detailed understanding of their surface chemistry is required to meet the technological applications of NWs. For example, the chemical and electronic stability of the surface of NWs is particularly important for applications including nanowire-based logic elements and chemical and biological sensors, which require direct interfacing with their surrounding environment. While there have been many efforts to chemical modifications of carbon nanotubes, there have been a few reports on chemical modifications of NWs. Silicon nanowires (SiNWs) have recently attracted a great deal of attention because silicon (Si) is of technological importance in microelectronics. Many successful synthetic strategies have now been developed to obtain bulk quantities of SiNWs using both gas-phase and condensed-phase techniques with or without metal catalysts. The chemical nature of the Si surface has also been studied in detail. Si forms a very stable oxide and can be chemically passivated with a number of organic species. The reaction mechanisms have extensively been investigated for solution-phase and vapor-phase oxidation, metallization, nitridation, and organic monolayer-based passivation of both Si surfaces of singlecrystal substrates and surfaces of porous Si. Therefore, SiNWs are a very good candidate for studying chemical modifications of NW surfaces, and in this Note we report the chemical modification of SiNWs by a combination of the formation of covalently bonded, organic monolayers on the surface of SiNWs and successive surface organic reactions. Boron-doped, single-crystal SiNWs were synthesized by gold nanocluster-catalyzed chemical vapor deposition with SiH4/B2H6 (1000 : 1 or 4000 : 1) as a vapor-phase reactant by following the reported procedure. The average diameter of SiNWs was ~40 nm and the length of SiNWs was 3-6 μm (Figure 1). The gradual bending of SiNWs may be due to elastic strains on the very small diameter of the wires. Figure 1. FE-SEM image of synthesized boron-doped Si nanowires.

Synthesis of silicon nanowires using laser ablation method and their manipulation by electron beam

Size control of silicon nanowires (SiNWs) synthesized by laser ablation of a Si target with iron or nickel as catalysts were investigated by changing the synthesis parameters such as the content of catalyst in targets and laser power during synthesis. The diameter and length of SiNWs significantly depended on the synthesis parameters, i.e. the size of SiNWs can be controlled by the synthesis parameters. Manipulation of SiNWs was also performed during the observation of scanning electron microscope. By changing the degree of charge-up for free-standing adjacent intertwined SiNWs at an edge of Si substrate, the distance and speed of opening motion of them can be controlled. This motion is probably caused by the Coulomb repulsive interaction between them.