Exciton-assisted tunneling transport in heterojunction microstructures

Longitudinal tunneling transport in the low-dimensional heterojunction structures induced by the excitonic Coulomb interaction has been formulated and discussed in the framework of Fermi's golden rule. We have investigated the tunneling transition of free carriers to quantum-well Wannier-Mott excitons incorporated in the sequential tunneling Hamiltonian. The modeling is evaluated by a set of coupled rate equations involving subband states of electron. hole and exciton. The exciton-assisted tunneling (EAT) phenomenon has its characteristic fingerprint causing tunneling current prior to the resonance electric fields, and a significant modulation of the I-V characteristics. It is also found that the bias offset and the FWHM of the EAT current spectrum can be comparable to that of resonant tunneling (RT) current, depending both on the 2D hole density of the confined subband and the excitonic properties in the active region. The EAT effect has a different I-V spectral line shape, compared to that of the RT or its replica, tailing off in the resonance regime induced by the exciton binding energy. (C) 1997 Academic Press Limited.