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

摘要

We calculate the strain and stress state and the polarization in pseudomorphic wurtzite MgZnO/ZnO and CdZnO/ZnO heterostructures as a function of the polar angle 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 and are opposite. Among the consequences are: (i) the epilayer strain energy has a minimum between and for semipolar growth plane close to ; (ii) for nonpolar growth () 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 ) between 0 and . Also we give useful analytical formula within an isotropic approximation for the compliances. Elastic strain energy (in relative units) of pseudomorphic wurtzite (Mg,Zn)O/ZnO and (Cd,Zn)O/ZnO heterostructures as a function of the polar angle between interface normal and the c-axis