Optical study of segregation effects on the electronic properties of molecular-beam-epitaxy grown (In,Ga)As/GaAs quantum wells
Indium segregation in InxGa1-xAs/GaAs (0.3<x less than or equal to 0.5) quantum wells grown by molecular-beam epitaxy and its influence on their electronic properties are investigated using thermally detected optical absorption. A kinetic model is used to derive concentration profiles and applied to interpret experimental data. The dependence of the In surface segregation on growth temperature and growth rate is studied. It is shown that a decrease of the substrate temperature is the best method to limit the segregation process kinetically. From a fit of the kinetic model to experimental data, the conduction-band offset ratio Q(c) is found to be independent of indium composition x between 0.2 and 0.5 (Q(c)=0.64+/-0.01). The exciton wave function is calculated using a variational technique involving a transfer-matrix formalism to study the influence of potential shape on excitonic properties. Only a slight increase in oscillator strength with In segregation is observed for the fundamental excitonic transition.