III-V nanowire heterostructures for quantum technologies: from 1D to 0D quantum confinement

Future quantum communication based on solid state platforms requires developing novel single photon sources (SPSs) integrated into photonic chips. QD in NW (QD-in-NW) structures appears convenient platforms for fabrication of future SPSs, allowing (i) the release of structural constraints in the choice of different materials, and (ii) improved light extraction due to the NW wave-guiding effects. Both radial (core-multishell) and axial composition-modulated heterostructures are being studied to exploit quantum-confinement in III-V NWs. In core-multishell NWs, size quantization from 2D to truly 1D is demonstrated; 0D quantization could be further obtained in these structures due to potential/size fluctuations within the shell materials. The optical/structural properties of MOVPE-grown GaAs-AlGaAs core-shell NWs are presented: a first ever estimate of the GaAs near band-edge absorption enhancement factor (in the 22−190 range) with respect to bulk GaAs is demonstrated, ascribed to improved wave-guiding behavior of incident light into the GaAs core by the surrounding AlGaAs shell. Insertion of a thin (few nm) GaAs shell in between two AlGaAs barrier shells was grown by MOVPE to form a quantum well tube (QWT) structure. QWT emissions in individual GaAs-AlGaAs core-multishell NWs were studied by low-temperature cathodoluminescence (CL) measurements, and exciton localization at QWT thickness fluctuations was observed.