THE ROLE OF VERTICAL TRANSPORT AND CAPTURE OF ELECTRONS AND HOLES FORTHE TRANSIENT OPTICAL-RESPONSE IN QUANTUM-WELL HETEROSTRUCTURES

The transient optical response of quantum wells (QWs) after optical an d electrical carrier injection into the barrier layers is studied expe rimentally and theoretically. We have varied the transport geometry in GaAs/AlGaAs and InGaAs/InAlGaAs heterostructures and emphasize the ba sic principles for a theoretical treatment of electron and hole captur e into QWs for a proper description of vertical carrier transport in t he barriers of QW heterostructures. Comparing our experimental data wi th the results of theoretical model calculations, we determine the cap ture, reflection and transmission probabilities, the ambipolar diffusi vities and the ambipolar mobilities in the barriers of GaAs/AlGaAs, as a model system. The temporal evolution of the electron and the hole c apture current densities at the QWs are studied in detail for a wide v ariation of the injected carrier densities. Amplitude modulation exper iments are performed for InGaAs/InAlGaAs QW laser devices providing in creasing 3 dB frequencies for decreasing confinement layer thickness, indicating the influence of carrier transport in the barriers.