FORMALISM FOR TUNNELING OF MIXED-SYMMETRY ELECTRONIC STATES - APPLICATION TO ELECTRON AND HOLE TUNNELING IN DIRECT-BAND AND INDIRECT-BAND-GAP GAAS/ALXGA1-XAS STRUCTURES

A formalism is presented to determine the tunneling properties of semiconductor heterostructures by studying the time evolution of multiband electronic states of mixed central-cell symmetry. The time evolution of the multiband wave function is determined by numerically solving the Schrodinger equation with use of a unitary approximation of the time-evolution operator valid for infinitesimal time steps. The valence-band states are studied with use of a four-band k.p approach, and results presented for resonant tunneling of holes in coupled quantum wells. The tunneling of an electron wave packet from a GaAs well through direct- and indirect-band-gap Al(x)Ga(1-x)As barriers is studied with use of the tight-binding representation for the conduction-band states in an eight-element (sp3) basis. The strong suppression of tunneling for the indirect-band-gap case is explained by the central-cell-symmetry variation in real space.