  The great possibilities for strain engineering in core/shell nanowires have
been explored as an alternative route to tailor the properties of binary III-V
semiconductors without changing their chemical composition. In particular, we
demonstrate that the GaAs core in GaAs/In(x)Ga(1-x)As or GaAs/In(x)Al(1-x)As
core/shell nanowires can sustain unusually large misfit strains that would have
been impossible in conventional thin-film heterostructures. The built-in strain
in the core can be regulated via the composition and the thickness of the
shell. Thick enough shells become almost strain-free, whereas the thin core
undergoes a predominantly-hydrostatic tensile strain, which causes the
reduction of the GaAs band gap energy. For the highest strain of 7 % in this
work (obtained for x=0.54), a remarkable reduction of the band gap by 40 % was
achieved in agreement with theoretical calculations. Such strong modulation of
its electronic properties renders GaAs suitable for near-infrared
nano-photonics and presumably high electron mobility nano-transistors.
