EVIDENCE OF STRONG SEQUENTIAL BAND FILLING AT INTERFACE ISLANDS IN ASYMMETRIC COUPLED QUANTUM-WELLS

We report the observation of relative saturation among excitonic emiss ion peaks at different sets of interface islands in growth-interrupted asymmetric-coupled quantum well GaAs/Al0.2Ga0.8As structures. The sat uration is due to sequential filling of excitonic states at different sets of interface islands. In contrast to free excitonic states, the s mall total area density of excitonic states at the interface islands m akes their filling observable at much lower excitation levels. As a re sult of the relative saturation, an effective blue shift of the appare nt excitonic emission peak at the islands, with a magnitude as large a s similar to 6.1 meV is observed when the excitation intensity increas es from similar to 1.6 to similar to 215 W cm(-2). The highest intensi ty required to observe the effective blue shift is about two orders of magnitude lower than that needed to observe a similar effect in a fre e excitonic emission peak. (C) 1997 Academic Press Limited.