Optical imaging spectroscopy of V-groove quantum wires: from localized to delocalized excitons

The exciton localization and delocalization is studied in GaAs/GaAlAs V-shaped quantum wires (QWRs) by microscopy and spectroscopy. Scanning optical imaging of different generations of samples shows that the localization length has been enhanced as the growth techniques were improved. In the best samples, excitons are delocalized in islands of length of the order of View the MathML source, and form a continuum of 1D states in each of them. On the opposite, in the previous generation of QWRs, the localization length is typically View the MathML source and the QWR behaves as a collection of quantum boxes. These localization properties are compared to structural properties and related to the progresses of the growth techniques. The presence of residual disorder is evidenced in the best samples and explained by the separation of electrons and holes due to the large built-in piezo-electric field in the structure.