Silicon nanowires: Preparation, device fabrication, and transport properties

The preparation of 20 +/- 5 nm diameter Si nanowires and the electrical cha racterization of Si nanowire devices are presented. The nanowires were grow n at 450-500 degreesC on solid substrates via the vapor-liquid-solid mechan ism using Au or Zn nucleation catalysts and SiH4 as the silicon source. The wires were investigated by high-resolution transmission electron microscop y. Two types of wires were found, as characterized by different growth dire ctions ([11 (1) over bar] and [211]). Several types of devices, including c rossed nanowire devices, four- and six-terminal devices, and three-terminal (gated) devices, were fabricated. For certain devices, various electrode c ompositions were also studied. The measured resistivity of these nanowires was separated from the contact resistance and could be varied from >10(5) O hm cm to similar to 10(-3) Ohm cm. The wide variation in resistivity was re lated to the nature of the electrical contact to the wires (Schottky or Ohm ic) and to the doping level of the wires. Doping of the nanowires was perfo rmed by the thermal diffusion of metal catalyst into the nanowires at 750-8 50 degreesC. Au nucleated nanowires exhibited resistivity values much lower than those of similarly treated Zn nucleated nanowires. This result is att ributed to the much larger relative solid solubility of gold in silicon.