  We study the dynamics of excitons in GaAs/(Al,Ga)As core-shell nanowires by
continuous-wave and time-resolved photoluminescence and photoluminescence
excitation spectroscopy. Strong Al segregation in the shell of the nanowires
leads to the formation of Ga-rich inclusions acting as quantum dots. At 10 K,
intense light emission associated with these shell quantum dots is observed.
The average radiative lifetime of excitons confined in the shell quantum dots
is 1.7 ns. We show that excitons may tunnel toward adjacent shell quantum dots
and nonradiative point defects. We investigate the changes in the dynamics of
charge carriers in the shell with increasing temperature, with particular
emphasis on the transfer of carriers from the shell to the core of the
nanowires. We finally discuss the implications of carrier localization in the
(Al,Ga)As shell for fundamental studies and optoelectronic applications based
on core-shell III-As nanowires.
