LOCALIZATION OF EXCITONS IN ULTRATHIN CDS ZNS QUANTUM STRUCTURES/

Monolayer fluctuations in ultrathin, coherently strained CdS/ZnS quant um-well structures result in a very strong localization of excitons. T he deepest localized excitons can be considered as individual, decoupl ed and three-dimensionally confined. Consequently, the optical propert ies can be well explained by transitions from an ensemble of spatially distributed, quasi-zero-dimensional excitonic states. The efficient p hotoluminescence (PL) and the optical gain in the deep-blue spectral r ange exhibit unusually broad and unstructured spectra. In mu-PL measur ements of a mesa-etched SQW sample (10 mu m x 10 mu m mesas down to 10 0 nm x 100 nm mesas) single, ultranarrow luminescence lines can be res olved when the number of luminescing states is reduced. (C) 1998 Elsev ier Science B.V. All rights reserved.