Local disorder and optical properties in V-shaped quantum wires: Toward one-dimensional exciton systems

The exciton localization is studied in GaAs/GaAlAs V-shaped quantum wires (QWR’s) by high spatial resolution 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 $1\mu \mathrm{m},$ and form a continuum of one-dimensional states in each of them, as evidenced by the $\sqrt{T}$ dependence of the radiative lifetime. On the opposite, in the previous generation of QWR’s, the localization length is typically 50 nm 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 piezoelectric field present in the structure.