Enlarged wells as probes to study superlattices

Within GaAs/Ga_1?xAl_x As MBE grown superlattices (SL), a few GaAs wells have been purposely enlarged. Calculations show that enlarged wells introduce localized states in the SL band gap: the distance between such a localized state and the bottom of the SL conduction band (or the top of the SL valence band) depends on the SL period and the enlarged well size. Luminescence and photoluminescence excitation results obtained on samples with different periods and enlarged well sizes are in good agreement with calculations.Once characterized, enlarged wells serve as probes in the study of SL optical and electrical properties. As examples, they were used to observe one monolayer size fluctuations and vertical transport by luminescence in GaAs/Ga_1?xAl_xAs superlattices.