Resonant tunneling in zero-dimensional nanostructures.

Abstract

Resonant tunneling through a semiconductor quantum nanostructure, consisting of laterally confined contact regions, barriers, and a laterally confined quantum well (quantum box), has been observed recently. Fine structure in the resonant tunneling has been attributed to the discrete density of states in the quantum box. We investigate two mechanisms to explain the fine structure in the quantum-box resonant tunneling (QBRT). In QBRT the carrier can tunnel through the structure without changing its lateral subband, just as the electron in normal resonant-tunneling tunnels without changing its lateral wave vector. However, the lateral states are discrete in QBRT, and resonant tunneling should occur at different applied biases for different subbands. The discrete density of lateral states produces one peak in the resonant tunneling current for each well state and occupied source-contact subband. We determine the conditions necessary to resolve structure that is due to the discrete lateral levels. Even when only one source-contact lateral subband is occupied, tunneling through other levels will occur if subband mixing at the interfaces, due to lateral wave-function mismatch at the interfaces, is possible. We determine the strength of subband mixing at an interface necessary to produce structure in the resonant-tunneling current. The second mechanism does not occur in normal resonant tunneling because the lateral wave vector is conserved during tunneling. Subband mixing produces two sets of fine structure. The first set appears for any contact-subband filling. The second set of peaks, which alternate with the first set of peaks, appears when two or more subbands are occupied. The results are used to better understand the recent observation of QBRT.