TUNNELING OF LASER-GENERATED FREE-ELECTRONS IN SEMICONDUCTOR DOUBLE WELLS

A theoretical study of the dynamics of free photogenerated carriers in resonance-biased asymmetric GaAs-AlxGa1-xAs double wells is presented. We consider a situation where photogeneration takes place on a subpicosecond time scale and, initially, produces a coherent ensemble of free electron-hole pairs in the wide well. The simultaneous thermalization and tunneling of electrons between the two wells is analyzed within the density matrix approach. The interplay between tunneling and Coulomb scattering is explored at several levels of approximation regarding free-carrier screening. We find that the Coulomb interaction represents an effective agent to destroy phase coherence and to damp out coherent charge oscillations in the system. Our calculations predict that, if the free-carrier Coulomb interaction provides the dominant dephasing mechanism in the system, coherent charge density oscillations associated with free carriers should persist up to electron sheet densities of about 3 x 10(10) cm(-2). It is shown that, under present conditions, dynamic screening within the plasmon-pole approximation and static screening give virtually identical results.