Electrical Contact Resistance of Bismuth Telluride Nanowires

With increasing miniaturization in microelectronics, one of the challenges to maintaining device performance is the management of excess heat. The room-temperature thermoelectric efficiencies of bismuth telluride (BiTe) compounds are the highest reported for any material. Therefore, BiTe nanowires are interesting as building blocks of thermoelectric circuits that can be used for heat management. Further improvements in nanoscale thermoelectrics may lead to new applications such as nanoscale room temperature coolers and generators, and uncooled bolometers. The exploitation of the thermoelectric properties of devices based on nanowires of thermoelectric materials requires good electrical contacts between the nanowires and metal electrodes and this is the subject of the present report. We present a study of the contact resistance and methods for controlling its value in individual bismuth telluride nanowires. The wires are fabricated by employing a two step method. First, dense arrays of 200-nm bismuth telluride nanowires are prepared by a nonlithographic fabrication technique consisting of the pressure injection of an alumina template with molten bismuth telluride. In the second step, individual nanowires are removed from the template by etching the alumina. The two step method has the advantage that, as we will show, some of the nanowires´ properties can be characterized by performing measurements on the arrays. In our investigations, we employed a simple device consisting of attaching a bismuth telluride nanowire to two gold planar electrodes. We find that the contact resistance has the potential of being non-ohmic and therefore lead to non-equilibrium