We study and compare the behavior of the left- and right-tunneling times of electrons quasiconfined in asymmetric double-barrier structures as a function of the bias for two different doping configurations in the electrodes: uniform doping and gradual doping. The potential experienced by the electrons is calculated self-consistently for each case by simultaneously solving the Schrödinger and Poisson equations. Afterwards, the stabilization method is employed to calculate the corresponding tunneling times. The case of gradual doping is especially interesting because an accumulation layer appears when the voltage is high enough. To analyze the stabilization graphs in the range of voltages where the two-dimensional quasiconfined level in the emitter interacts with the quantum-well level we have introduced a three-level model. We present a comparison of the tunneling times calculated for the two doping profiles with the ones obtained with a model potential. Finally, charge-accumulation effects are analyzed in the gradually-doped case and critically discussed within the framework of available experimental data.

• Received 27 May 1994

DOI:https://doi.org/10.1103/PhysRevB.50.11884