The fabrication of silicon nanowire-based solar cells on silicon wafers and on multicrystalline silicon thin films on glass is described. The nanowires show a strong broadband optical absorption, which makes them an interesting candidate to serve as an absorber in solar cells. The operation of a solar cell is demonstrated with n-doped nanowires grown on a p-doped silicon wafer. From a partially illuminated area of 0.6 cm(2) open-circuit voltages in the range of 230-280 mV and a short-circuit current density of 2 mA cm(-2) were obtained.

Silicon nanowire field effect transistors (Si NW FETs) are emerging as powerful sensors for direct detection of biological and chemical species. However, the low sensitivity of the Si NW FET sensors toward nonpolar volatile organic compounds (VOCs) is problematic for many applications. In this study, we show that modifying Si NW FETs with a silane monolayer having a low fraction of Si-O-Si bonds between the adjacent molecules greatly enhances the sensitivity toward nonpolar VOCs. This can be explained in terms of an indirect sensor-VOC interaction, whereby the nonpolar VOC molecules induce conformational changes in the organic monolayer, affecting (i) the dielectric constant and/or effective dipole moment of the organic monolayer and/or (ii) the density of charged surface states at the SiO(2)/monolayer interface. In contrast, polar VOCs are sensed directly via VOC-induced changes in the Si NW charge carriers, most probably due to electrostatic interaction between the Si NW and polar VOCs. A semiempirical model for the VOC-induced conductivity changes in the Si NW FETs is presented and discussed.

Silicon nanowire field-effect transistors (Si NW FETs) have been used as powerful sensors for chemical and biological species. The detection of polar species has been attributed to variations in the electric field at the conduction channel due to molecular gating with polar molecules. However, the detection of nonpolar analytes with Si NW FETs has not been well understood to date. In this paper, we experimentally study the detection of nonpolar species and model the detection process based on changes in the carrier mobility, voltage threshold, off-current, off-voltage, and subthreshold swing of the Si NW FET. We attribute the detection of the nonpolar species to molecular gating, due to two indirect effects: (i) a change in the dielectric medium close to the Si NW surface and (ii) a change in the charged surface states at the functionality of the Si NW surface. The contribution of these two effects to the overall measured sensing signal is determined and discussed. The results provide a launching pad for real-world sensing applications, such as environmental monitoring, homeland security, food quality control, and medicine.

For many applications, the presence of oxide on Si nanowires (Si NWs) is undesirable because of the difficulty in controlling the SiO 2 /Si interface properties. Here, we report on the functionalization of 50 nm (in diameter) Si NWs with alkyl chains using a versatile two step chlorination/alkylation process, while preserving the original length and diameter of the NWs. We show that Si NWs terminated with C 1 -C 10 molecules, through Si-C bonds, connect alkyl molecules to 50-100% of the Si atop sites and provide surface stability that depends on the chain length and molecular coverage. These observation were explained by noting that the longer the alkyl chain the higher the concentration of molecule-free pinholes on the Si NW surfaces and, therefore, the easier the oxidation process. Our results provide evidence that alkyl-Si NWs provide stronger Si-C bonds and higher surface stability in ambient conditions than equivalent two-dimensional (2D) Si surfaces having similar or higher initial coverage. The kinetic mechanism of the alkylation process of Si NW surfaces, the oxidation resistance of the modified structures, and the differences from 2D surfaces are discussed in the article.

We report on the functionalization of Si NWs with C 1 -C 6 alkyl chains using a versatile two step chlorination/ alkylation process. We show that Si NWs terminated with C 1 -C 6 molecules, through Si-C bonds, connect alkyl molecules to 50-100% of the Si atop sites and provide surface stability that depends on the chain length and molecular coverage, according to the following order: COur results indicate that the oxidation resistance of (C 1 -C 2 )-Si NWs is significantly higher than equivalent 2D Si(100) surfaces, whereas (C 3 -C 6 )-Si NWs are comparable to 2D (C 3 -C 6 )-Si(100). These discrepancies can be explained as follows: the lower the molecular coverage, the higher the probability for interaction between oxidizing agents (O 2 or H 2 O) and molecule-free sites. Our results are of practical importance when reduced amounts of oxide are required, e.g., for radial epitaxy on NWs to realize vertical P-N junctions for solar cells or for radial Si/Ge superlattices for application in optoelectronics.