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Pseudomorphic ZnO‐based heterostructures: From polar through all semipolar to nonpolar orientations

We calculate the strain and stress state and the polarization in pseudomorphic wurtzite Mg x Zn 1−x O/ZnO and Cd x Zn 1−x O/ZnO heterostructures as a function of the polar angle θ between the c‐axis and the epitaxial direction. (Cd,Zn)O/ZnO behaves qualitatively similar to the systems (In,Ga)N/GaN and (Al,Ga)N/GaN. (Mg,Zn)O/ZnO represents a unique case since the signs of the change of lattice constants ∂a/∂x and ∂c/∂x are opposite. Among the consequences are: (i) the epilayer strain energy has a minimum between 0∘ and 90∘ for semipolar growth plane close to (112‾2) ; (ii) for nonpolar growth ( θ=90∘ ) the strain in the epitaxial direction is close to zero; and the in‐plane polarization is large (comparable to the polar case); and (iii) the piezoelectric polarization along the growth direction has only one zero (at θ=90∘ ) between 0 ∘ and 180∘ . Also we give useful analytical formula within an isotropic approximation for the compliances.