  ZnTe/CdSe/(Zn,Mg)Te core/double-shell nanowires are grown by molecular beam
epitaxy by employing the vapor-liquid-solid growth mechanism assisted with gold
catalysts. A photoluminescence study of these structures reveals the presence
of an optical emission in the near infrared. We assign this emission to the
spatially indirect exciton recombination at the ZnTe/CdSe type II interface.
This conclusion is confirmed by the observation of a significant blue-shift of
the emission energy with an increasing excitation fluence induced by the
electron-hole separation at the interface. Cathodoluminescence measurements
reveal that the optical emission in the near infrared originates from nanowires
and not from two dimensional residual deposits between them. Moreover, it is
demonstrated that the emission energy in the near infrared depends on the
average CdSe shell thickness and the average Mg concentration within the
(Zn,Mg)Te shell. The main mechanism responsible for these changes is associated
with the strain induced by the (Zn,Mg)Te shell in the entire core/shell
nanowire heterostructure.
