Surface Trap-Induced Conductivity Type Switching in Semiconductor Nanowires: Analytical and Numerical Analyses

Due to high surface-to-volume ratio, surface traps play crucial role in electronic properties of semiconductor nanowires and nanowire-based devices. Recently, it was experimentally demonstrated that surface traps even can induce conductivity type inversion in semiconductor nanowires. Here, we have performed theoretical and numerical analyses to investigate the influence of surface traps on semiconductor nanowire conductivity including possible inversion due to surface traps. The Poisson equation with consideration of both type of mobile charges and ionized donors was solved having surface trapped charges in Neumann boundary conditions. Different semiconductor materials and surface trap densities have been considered. Calculations were done considering single energy level of surface traps and then the results were generalized to exponential energetic distribution of surface states density. The effect of surface traps was analyzed both for low-doped and highly doped nanowires. It was shown that for moderate or lightly doped NWs, the conductivity type switching from n- to p-type can occur at small radii. The developed potential-based analytical model allows calculating the inversion charge raised due to surface traps. The accuracy of analytical calculations has been validated with TCAD simulations and qualitatively compared with published experimental data. This paper is useful for design optimization of nanowire-based photodetectors, sensors, and reconfigurable FETs.