Direct measurement of surface states density and energy distribution in individual InAs nanowires

InAs nanowires are candidates for future high-speed electronic and optoelectronic applications due to their high electron mobility and large coherence length. However, InAs surfaces are known to possess a high concentration of donor-type surface states, which results in an electron accumulation layer and, consequently, Fermi level pinning. Since the surface to volume ratio in nanowires is very large, the effect of surface states is greatly enhanced. We present a method for directly determining the density and energy distribution of single nanowire surface states using Kelvin probe force microscopy measured on a nanowire field-effect transistor and interpreted by electrostatic modeling. Here, the method is applied to individual InAs nanowires, which similarly to bulk InAs exhibit a prominent accumulation layer consisting of a large concentration of donor-type surface states. Nevertheless, due to the small diameter of the nanowires, the electron accumulation and Fermi level pinning take place within the entire nanowire.