The change in the piezoelectric polarization P p at the core-shell interface is given by -∆P p = σ p = ε x ′ x ′ e 31 cos θ + ε y ′ y ′ {e 31 cos 3 θ + [(e 33e 15 )/2] sin θ sin 2θ} + ε z ′ z ′ {[(e 31 + e 15 )/2] sin θ sin 2θ + e 33 cos 3 θ} + ε y ′ z ′ [(e 31e 33 ) cos θ sin 2θ + e 15 sin θ cos 2θ], where the primed variables denote transformed coordinates in (x ′ , y ′ , z ′ ) space, θ = ϕ + π, and the piezoelectric tensor components e i j are taken from Ref. . Strain forces in the core and shell resulting from lattice mismatch have been calculated in three dimensions using several methods. For instance, the atomistic valence force-field model has been applied to hexagonal core-shell GaN/AlN NW systems and continuum elasticity theory to cylindrical core-shell NW Si/Ge geometries . Each of these prior studies indicates the interfacial strain discontinuity is similar to that of a thin film, and strain gradients within the shell are less significant than those near the interface. As such, we neglect volumetric contributions to the piezoelectric polarization of the shell and focus exclusively on the interfacial component derived from planar film expressions for each orientation considered in this work. Prior studies have also indicated that the relatively low strain in these structures allows us to safely disregard its influence on effective masses and bandgaps .