"Electronic transport in nanostructures: why size matters"

A. Alec Talin

Center for Nanoscience and Technology, NIST, Gaithersburg, MD

Nanowires continue to fascinate researchers, who are often motivated by the combination of high crystalline quality and nanoscale dimensions not easily accessible by 'top-down' lithographic means. The 'size-effect' frequently sited in nanowire literature is that of quantum confinement, i.e., where the density of states assumes a 1-dimensional character. These dimensions, typically <20 nm in diameter, are, in fact, seldom fabricated in practice. In my talk, I will discuss how finite dimensions, far from the quantum confinement limit, affect bulk and contact mediated transport in nanowires. Specifically, I will show that the onset of space charge limited conduction in nanowires occurs at a lower critical voltage, and has a different geometric scaling as compared to low aspect ratio specimens (i.e. thin films). I will also discuss measurement where we have probed the transport characteristics of the metal catalyst/nanowire contact in the Au /Ge-nanowire system, demonstrating the presence of a Schottky barrier at the interface. Surprisingly, we find that the small bias conductance increases with decreasing diameter. Our model suggests that this effect arises because electron-hole recombination in the depletion region is the dominant charge transport mechanism, with a diameter dependence of both the depletion width and the electron-hole recombination time. Time permitting, I will also discuss our recent characterization of transport in InAs nanowires, including real-time observation of thermal breakdown, and its implications for both electronic and thermal transport in this system.