Nano Lett. 13, 6183–6188 (2013)

The electrical contact between a metallic electrode and a semiconductor in electronic devices creates an energy barrier for the injection or extraction of electrons. The barrier height determines the ease of electron transfer and affects device performance. It can be estimated by analysing the current–voltage characteristics. However, in the case of semiconductor nanowires, this method has limited applicability due to complications that arise from the small dimensions of the devices. Lincoln Lauhon and colleagues at Northwestern University and Tel-Aviv University now show that the height of the barrier between a metal contact and an n-doped silicon nanowire can be measured by spectrally resolved scanning photocurrent microscopy.

The researchers shine sub-bandgap light on the metal–nanowire junction. Electrons in the metal are photoexcited and can cross the energy barrier in a process called internal photoemission. This generates a photocurrent that is collected by the microscope. The barrier height can then be extracted by analysing the dependence of the photocurrent on the energy of the photoexcitation. Lauhon and colleagues find that the height is lowered compared with the case of metal/bulk silicon interfaces as a consequence of doping and geometric effects. Nanowires with enhanced surface doping or smaller diameters exhibit reduced barrier heights. The method could also be used to characterize the barrier height in other nanoscale heterojunctions.