Diameter-dependent internal gain in ZnO micro/nanowires under electron beam irradiation

We observed a conductivity gain in intrinsic ZnO micro/nanowires at characteristic diameter scales from nanoscale to microscale by employing metal-semiconductor-metal structures with ohmic contacts under electron beam irradiation. The conductivity is enhanced under electron beam illumination and the magnitude is inversely proportional to the micro/nanowire diameter from 400 nm to 1300 nm at constant radiation intensity. We also introduced a model to simulate the diameter-dependent electric potential distribution. We attribute these observations to the variation of the effective electron carrier density upon varying diameters of ZnO micro/nanowires, as a result of field effects from the diameter-dependent population of the surface-trapped holes.