Comparative analysis of sequential and coherent tunneling models in resonant diodes

Abstract

We compare the sequential and coherent tunneling models for the current voltage $(I\text{\ensuremath{-}}V)$ characteristic and shot noise suppression in double-barrier resonant diodes. The results confirm that the $I\text{\ensuremath{-}}V$ characteristic remains the same for the two models, while at increasing voltage the shot noise power at zero frequency shows significant differences. In sequential tunneling, shot noise exhibits in general two regions of suppression due to Pauli and Coulomb correlations, respectively, and with the associated Fano factor never dropping below the value of 0.5. By contrast, in coherent tunneling shot noise exhibits a single region of suppression with the associated Fano factor having the possibility of dropping below the value of 0.5 at voltages near to the current peak. We also investigate the current spectral density and the Fano factor as a function of frequency up to values below that corresponding to the energy difference between the first and the second resonant electron states. At all frequencies the Fano factor for sequential tunneling never drops below the value of 0.5. By contrast, for coherent tunneling, at high frequencies the Fano factor is found to become suppressed systematically below the value of 0.5 to a minimum value of 0.25 which is independent of frequency. These results confirm that coherent tunneling can lead to shot noise suppression below the value of 0.5 contrary to the case of sequential tunneling.