Photoluminescence from core/multiple-shell GaAs/AlGAs Nanowires

We use photoluminescence (PL) and photoluminescence excitation spectroscopy (PLE) to study the electronic structure of GaAs/AlGaAs core multi-shell NWs. Using Au-catalyst assisted MOCVD, a nominally 2~nm GaAs quantum well tube (QWT) with AlGaAs barriers is formed surrounding a central 50~nm GaAs nanowire core. PL measurements on single nanowires reveal a line at the expected exciton energy for the core and, in addition, several higher energy lines not observed in simple core/shell structures. PLE measurements suggest a coupling of the confined states in the QWT and the core states. A broad PLE response centered at 1.67~eV is suggestive of an AlGaAs shell concentration of approximately 12{\%}. We acknowledge the support of the NSF~(0701703 and 0806700) and the Australia Research Foundation.