Realization of Stranski-Krastanow InAs quantum dots on nanowire-based InGaAs nanoshells

We investigate the formation and optical properties of InAs quantum dots on an InGaAs nanosubstrate. We find that Stranski-Krastanow InAs quantum dots are hardly formed on Au-catalyzed InGaAs nanowires due to the phase separation as well as stacking faults. High-quality Stranski-Krastanow InAs quantum dots are realized on a pure zinc blende InGaAs shell radially grown on a GaAs nanowire core. The quantum dots have a large size and regular shape, residing on a wetting layer of several nanometers. For optical characterization, we fabricate a "dot-in-well" structure by capping the quantum dots with InGaAs/GaAs double layers. Photoluminescence from the quantum dots is observed at 77 K, with a peak wavelength of 954 nm, which is distinctly redshifted compared with that of InAs quantum dots directly grown on GaAs nanowires. This work shows the potential of growing Stranski-Krastanow QDs on more types of NWs and obtaining longer wavelengths for wider applications.