GREENS-FUNCTION STUDY OF THE ELECTRON-TUNNELING IN A DOUBLE-BARRIER HETEROSTRUCTURE

The quasi-one-dimensional aspects of the electron tunneling through AlAs/GaAs/AlAs (001) double-barrier structures have been investigated using the tunneling formalism based on the nonequilibrium Green's function developed by Keldysh. In describing the electronic structure of a double-barrier heterostructure, Green's-function formulation of scattering theory incorporated with the multiorbital tight-binding model is used, so as to take into account the effects of indirect band gap, band nonparabolicity, and multiple orbitals in the aperiodic layered structure. The effect of high external bias on the junction is solved exactly within this model. The electron-tunneling situation and the effect of the X-valley originated barrier confined states on the electron tunneling are analyzed with the spectral local density of states of the double-barrier structure in the [001] direction under the external bias. The calculated current density J(k(parallel to)=0) versus voltage curve exhibits the structures for the interlayer intervalley electron transfer, which are manifested as the electron propagation through Gamma-valley originated states and through X-valley barrier confined states. The smaller current peak-to-valley ratios are found in the double-barrier structures with thicker barriers, which is consistent with the experimental results. The enhancement of Gamma-X interlayer intervalley electron transfer and reduction of the Gamma-Gamma resonant electron interlayer transfer is found with the increase of the phenomenological imaginary potential term.