Geometry- and size-dependence of electrical properties of metal contacts on semiconducting nanowires

We report on a theoretical study of the geometry-and size-dependent effects of metal-semiconductor contacts to understand the origins of significant contact effects on nanowire (NW) devices. The difference in metal-semiconductor barrier width and height for a planar and NW device is calculated based on the differences in depletion-layer width and image-force barrier-lowering effects. We calculate the ratio of the specific contact resistance of a NW contact to that of a planar contact assuming the two systems have been made of the same material set. Using a modified cylindrical transmission line model, we compare the effects of contacts in the two systems and discuss the reasons for larger contact effects in NW devices. The study suggests that the formation of a higher doping concentration in the contact regions is essential for better NW transistors.