Inner composition, defects and morphology of AlGaAs nanowires grown by Au-catalyzed MOVPE

The inner composition, defect content and morphology of AlGaAs nanowires (NWs) grown on (111)B-GaAs by Au-catalyzed MOVPE is reported. The NWs grow tapered with their [111] axis normal to the substrate. The Raman spectra of single AlGaAs NWs were measured in non-resonant conditions with sub-?-meter spatial resolution, allowing determination of the Al content. NWs consist of GaAs for T G<475°C, but show a two-fold compositional structure for T G>475°C, namely an Al xGa 1-xAs core surrounded by an Al yGa 1-yAs (y<x) shell, ascribed to the combination of Au-catalyzed (axial) and conventional (sidewall) growth. The cross-sectional shape of AlGaAs NWs changes from triangular (for T G=500÷525°C) to almost hexagonal (for T G=550°C), due to an exchange between {2 -11} and {110} planes as the slowest to grow. The NWs have free-electron concentrations ~10 18 cm -3, due to Si contamination of the Al source.