  We study the three-dimensional deformation field induced by an axial (In,Ga)N
segment in a GaN nanowire. Using the finite element method within the framework
of linear elasticity theory, we study the dependence of the strain field on the
ratio of segment length and nanowire radius. Contrary to intuition, the
out-of-plane-component of the elastic strain tensor is found to assume large
negative values for a length-to-radius ratio close to one. We show that this
unexpected effect is a direct consequence of the deformation of the nanowire at
the free sidewalls and the associated large shear strain components. Simulated
reciprocal space maps of a single (In,Ga)N/GaN nanowire demonstrate that
nanofocus x-ray diffraction is a suitable technique to assess this peculiar
strain state experimentally.
