Optical and electrical investigation of the population properties for quantum cascade structures

We have investigated the electric-field-dependent subband population and carrier dynamics in double-quantum-well superlattices (DQW-SLs) as well as quantum cascade structures (QCSs) of the GaAs/(Al,Ga)As material system by (interband) photoluminescence spectroscopy and current–voltage characteristics. In several DQW-SLs, absolute values for the subband population of electrons and the transfer coefficients of holes have been determined. In typical QCSs, the characteristic times for the hole relaxation into the widest well have been estimated to be of the order of several picoseconds. Although the characteristic times become very short, the electric-field-dependent population of the ground states in the active region can be qualitatively characterized.