  We report the detection of quantum confinement in single InAs-InP core-shell
nanowires. The wires having an InAs core with ~25 nm diameter are characterized
by emission spectra in which two peaks are identified under high excitation
intensity conditions. The peaks are caused by emission from the ground and
excited quantized levels, due to the quantum confinement in the plane
perpendicular to the nanowire axis. We have identified in the emission spectra
different energy contributions related to the wurtzite structure of the wires,
the strain between the wurtzite core and shell, and the confinement energy of
the InAs core. Calculations based on 6-band strain-dependent k.p theory allow
the theoretical estimation of the confined energy states in such materials and
we found these results to be in good agreement with those from the
photoluminescence studies.
