Excitonic recombination and absorption in InxGa1-xAs/GaAs heterostructure nanowires

Photoluminescence (PL), micro-PL, and PL excitation (PLE) spectroscopy for different light polarizations have been used to investigate the electronic properties of GaAs characterized by a dominant wurtzite (WZ) phase that forms in bare GaAs and in InGaAs/GaAs heterostructure (HS) nanowires (NWs). In both cases, the GaAs luminescence exhibits very narrow emission lines, which persist up to room temperature. At 10 K, the energy of the exciton ground state recombination of GaAs NWs is equal to 1.522-1.524 eV. In HS NWs, micro-PL combined with transmission electron microscopy pinpoints the tip of the GaAs section, with a dominant WZ phase, as the origin of that emission. In PLE, two very narrow excitonic absorptions at 1.523 and 1.631 eV involve different critical points of the WZ valence band (Gamma(9 nu) and Gamma(7 nu mu)). The low-energy peak shows a negligible Stokes shift with respect to PL. At 10 K, a further weak and broad PLE signal is found at 1.59 eV. The possible attribution of these lines within the present knowledge of the WZ band structure is critically discussed.