Conductivity Enhancement of Silicon Nanowires

Abstract

Current-voltage (I-V) characteristics for various silicon wires of different length-to-width ratios were numerically calculated by solving the Poisson equation and the current continuity equations for electrons and holes self-consistently. We found that, as the silicon wire became thinner or the length-to-width aspect ratio becomes higher, the I-V data deviated more from the Ohmic relation: the current density at a certain bias voltage was larger. In the case of a 500-nm-long silicon wire with n-type doping of 1 × 1016 cm3, for example, the current density of a silicon wire at a bias voltage of 2 volts increased by nearly threefold as the length-to-width ratio of wires was increased from 1 to 25. This behavior is attributed to an enhanced field at the source due to the strong stray field configuration near the contacts at both ends of a wire and to the large carrier build-up in the middle. Our result suggests that a classical treatment of nanowire transport with a proper account of the nonuniform field distribution along the wire may partly explain the conductivity enhancement phenomenon often observed in various nanowires and nanotubes.