Intersubband excitations in ultrathin core-shell nanowires in the one-dimensional quantum limit probed by resonant inelastic light scattering

We investigate single, ultrathin, pure-wurtzite-phase GaAs-AlGaAs core-shell nanowires by resonant inelastic light scattering (RILS). We observe electronic Raman excitations, which can be attributed to intersubband excitations of photoexcited electrons or holes within the quasi-one-dimensional (1D) subband structure. Our analysis reveals that the electronic systems in the narrowest investigated nanowires, with GaAs core diameters down to 25 nm, are in the 1D quantum limit. Excitation-density-dependent measurements indicate that the observed 1D intersubband excitations are mainly of single-particle origin, since no plasmonic shift can be deduced. Our experimental findings are consistent with a three-step scattering mechanism, based on the Coulomb interaction of photoexcited electron-hole pairs with free carriers, electrons, or holes. The quantized subband energies, as extracted from photoluminescence, photoluminescence-excitation, and RILS experiments, can be nicely reproduced by realistic multiband k center dot p band structure calculations, taking into account the hexagonal geometry of the nanowires.