Observation of free excitons in room-temperature photoluminescence of GaAs/AlGaAs single quantum wells.

Observation of free excitons is reported in room-temperature photoluminescence of nominally undoped GaAs/AlGaAs single quantum wells grown by molecular beam epitaxy. A comparative study with parallel-conduction photocurrent spectroscopy shows that a sharp luminescence peak with a linewidth of 14 meV observed for the 6.1-nm-wide well coincides within 2 meV with the n=1 heavy-hole free-exciton resonance line at excess carrier densities less than 1017 cm-3. Excitonic decay channels dominate the luminescence spectrum even at room temperature as a result of quantum confinement effects, although photogenerated carriers are also provided for photocurrents by exciton dissociations. [ABSTRACT FROM AUTHOR]