Decay times of one-dimensional excitons in GaAs/AlxGa1-xAs quantum-well wires.

We have investigated the time-dependent photoluminescence (PL) of GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum-well wires with GaAs cross sections of 70\ifmmode\times\else\texttimes\fi{}14 nm prepared by deep mesa etching into a quantum-well system. The decay times of the two lowest one-dimensional heavy-hole excitonic states, ${\mathrm{hh}}_{11}$ and ${\mathrm{hh}}_{12}$, are both about 300 ps at 5 K, which is surprisingly long and comparable to the PL lifetime of 450 ps of the heavy-hole exciton in the reference quantum-well sample. In the early-time regime, a population transfer from the ${\mathrm{hh}}_{12}$ excitonic state to the ${\mathrm{hh}}_{11}$ state occurs with a transfer time constant of 100 ps, which is explained by a cooling process due to acoustical-phonon scattering. Within this time, the PL is anisotropic for the different polarizations of the exciting radiation with respect to the wire direction. For larger delay times, the excitons lose their information on the polarization in the excitation beam due to the scattering processes.