GaAs-AlGaAs core-shell nanowire arrays: MOVPE growth and luminescence properties

We report on a detailed MOVPE-growth study of GaAs-AlGaAs core-shell nanowire arrays, and on their related photoluminescence (PL) properties. Validation of a mass transport vapour growth model of AlGaAs shell for nanowire arrays demonstrates the dependence of shell growth rate on nanowire size, height, and density; besides ensuring strict control over shell geometry, the model allows to calculate effective (around the nanowires) vapour conditions during shell growth. PL properties of core-shell nanowires were thus investigated as function of their relevant geometrical parameter, i.e. the shell-thickness to core-radius ratio and effective shell growth conditions. To account for built-in elastic strain effects on PL emission, strain fields in core-shell nanowires were determined by high-resolution XRD, and compared to values based on a uniaxial elastic energy equilibrium model. In addition to the expected strain-dependent red-shift on GaAs excitonic emission, the occurrence of a shell-dependent localization effect in present nanowires is reported and discussed.