EFFECT OF ALLOY DISORDER AND STRUCTURAL DEFECTS ON EXCITONIC PROPERTIES IN (100)-ORIENTED AND (311)-ORIENTED INGAAS/GAAS QUANTUM-WELLS

The properties of excitonic states in pseudomorphic, (100)- and (311)-oriented In0.2Ga0.8As/GaAs quantum well (QW) structures are investigated. Strained QW's with different states of strain and segregation were grown by molecular beam epitaxy. No growth interruption was carried out at the interfaces. This approach allows us to reduce the segregation effects in samples having (311)A orientation. As a result, quite sharp gaussian shaped excitonic transitions with line width of about 0.8 meV have been demonstrated. We find significant differences in the optical properties, growth kinetic and defect formation of samples for the three orientations. The ahoy disorder is smaller in the (311)A orientations than in the (311)B and(100) ones. An anomalous broadening of the excitonic line width is observed in case of samples having (311)B orientation and is accounted for structural defects other than those produced by alloy disorder. Surface wells are used in conjunction with In surface segregation and evaporation effects. Different activation energies for the indium desorption fi om the (311)A and B surfaces are obtained. We state that the different alloy and defect states are originated in the different strain relaxation mechanism and surface reaction kinetic in the three non equivalent (311)and (100) surfaces.