Tunnel transport through multiple junctions

TL;DR

This paper investigates electron transport through multi-layered junctions, revealing oscillatory conductance behavior and significant enhancements at certain layer thicknesses, using Green's function formalism and tight-binding models.

Contribution

It introduces a detailed analysis of conductance oscillations and enhancement in double and triple junctions, extending understanding beyond simple junctions.

Findings

Conductance decays exponentially in simple junctions with semiconductor thickness.

Double and triple junctions exhibit conductance oscillations with metal layer thickness.

Maximum conductance enhancement reaches up to 323% in triple junctions.

Abstract

We calculate the conductance through double junctions of the type M(inf.)-Sn-Mm-Sn-M(inf.) and triple junctions of the type M(inf.)-Sn-Mm-Sn-Mm-Sn-M(inf.), where M(inf.) are semi-infinite metallic electrodes, Sn are 'n' layers of semiconductor and Mm are 'm' layers of metal (the same as the electrodes), and compare the results with the conductance through simple junctions of the type M(inf.)-Sn-M(inf.). The junctions are bi-dimensional and their parts (electrodes and 'active region') are periodic in the direction perpendicular to the transport direction. To calculate the conductance we use the Green's Functions Landauer-B$\ddot{u}$ttiker formalism. The electronic structure of the junction is modeled by a tight binding Hamiltonian. For a simple junction we find that the conductance decays exponentially with semiconductor thickness. For double and triple junctions, the conductance oscillates with the metal in-between thickness, and presents peaks for which the conductance is enhanced by 1-4 orders of magnitude. We find that when there is a conductance peak, the conductance is higher to that corresponding to a simple junction. The maximum ratio between the conductance of a double junction and the conductance of a simple junction is 146 %, while for a triple junction it is 323 %. These oscillations in the conductance are explained in terms of the energy spectrum of the junction's active region.