Direct observation of ballistic and drift carrier transport regimes in InAs nanowires

Conductive atomic force microscopy has been used to characterize distance-dependent electron transport behavior in InAs nanowires grown by metal-organic chemical vapor deposition. Using a conducting diamond-coated tip as a local electrical probe in an atomic force microscope, the resistance of the InAs nanowire has been measured as a function of electron transport distance within the nanowire. Two regimes of transport behavior are observed: for distances of similar to 200 nm or less, resistance independent of electron transport distance, indicative of ballistic electron transport, is observed; for greater distances, the resistance is observed to increase linearly with distance, as expected for conventional drift transport. These observations are in very good qualitative accord with the Landauer formalism for mesoscopic carrier transport, and the resistance values derived from these measurements are in good quantitative agreement with carrier concentrations and mobilities determined in separate experiments. These results provide direct information concerning distances over which ballistic transport occurs in InAs nanowires as well as demonstrating the ability of the scanning probe techniques employed to characterize nanoscale transport characteristics in semiconductor nanowire structures.