INTERSUBBAND OPTICAL BISTABILITY INDUCED BY RESONANT-TUNNELING IN AN ASYMMETRIC DOUBLE-QUANTUM-WELL

An intrinsic optical bistability in a double quantum well is described theoretically. The effect is based on the resonant tunneling of elect rons against the electric-field force (the counterfield electron trans fer) and is driven and controlled by far-ir radiation exciting an inte rsubband transition. The theory relies on the density-matrix technique and takes into account optical intersubband excitation, interwell tun neling, the relaxation of populations and polarizations, and the mean- field effects of the transferred electron charge (shifts of the levels and changes of matrix elements). Hysteresis-type curves are obtained for both the charge-transfer probability and the optical absorption as functions of the light intensity. The theory shows the effect to be r eadily observable under realistic conditions, with the exciting-light intensity as low as 50 W/cm2.