AL 3P VALENCE AND EXCITONIC STATES IN GASB AL0.3GA0.7SB AND GAAS/AL0.3GA0.7AS HETEROSTRUCTURES AS A FUNCTION OF GROWTH-PROCESS/

Density of states (DOS) in GaSb/Al0.3Ga0.7Sb systems are studied by el ectron-induced x-ray emission spectroscopy (EXES) and compared to prev ious results we have obtained for GaAs/Al0.3Ga0.7As systems. The Al 3p valence DOS are analyzed in the bulk ternary compounds, in heterostru ctures, and in interfacial zones 30 Angstrom thick, this thickness bei ng equivalent to that of heterostructure layers. Large changes of the Al 3p valence DOS are seen, depending on the preparation conditions of the samples whose quality was checked by photoluminescence. For heter ostructures having a small interface roughness, localization of states on the whole valence band of barriers is evidenced. This localization is attributed to bidimensional effects that largely dominate the inte rface effects. In contrast, for heterostructures having interfaces of lower quality, interface interaction and localization are competitive, Core excitonic transitions seen by EXES confirm that localization of Al states in the barriers exists for superlattices with abrupt interfa ces.