  Magneto-photoluminescence measurements of individual zinc-blende GaAs/AlAs
core/shell nanowires are reported. At low temperature a strong emission line at
1.507 eV is observed under low power (nW) excitation. Measurements performed in
high magnetic field allowed us to detect in this emission several lines
associated with excitons bound to defect pairs. Such lines were observed before
in epitaxial GaAs of very high quality, as reported by Kunzel and Ploog. This
demonstrates that the optical quality of our GaAs/AlAs core/shell nanowires is
comparable to the best GaAs layers grown by molecular beam epitaxy. Moreover,
strong free exciton emission is observed even at room temperature. The bright
optical emission of our nanowires in room temperature should open the way for
numerous optoelectronic device applications.
