Built-in elastic strain and localization effects on GaAs luminescence of MOVPE-grown GaAs-AlGaAs core-shell nanowires

The core photoluminescence emission of MOVPE-grown GaAs-Al0.33Ga0.67As core-shell nanowires is studied as function of the relevant geometrical parameter of these nanostructures, namely the shell-thickness to core-radius ratio h(s)/R-c. The energy of the dominant emission peak was compared with values of the GaAs heavy- and light-hole excitons redshifted by a uniaxial tensile strain, the latter calculated assuming perfect coherence at the core/shell interface and elastic energy equilibrium within the nanowires. Good agreement is obtained for h(s)/R-c < 1, the intrinsic strain-free excitonic emission being identified at 1.510 eV, and further ascribed to bound heavy-hole excitons. For h(s)/R-c > 1 increasingly larger redshifts (up to similar to 9 meV in excess of values calculated based on our elastic strain model) are observed, and tentatively ascribed to shell-dependent exciton localization effects.