NONLINEAR PIEZOELECTRICITY IN CDTE

Nonlinear piezoelectricity has recently been detected in strained-layer superlattices where CdTe is pseudomorphically grown along (111) on different materials. We investigate this problem from first principles using density-functional theory. As a byproduct, we provide the ab initio calculation of several properties of this material, including the equilibrium lattice constant, Born effective charges, internal strain parameter, zone-center optical-phonon frequencies, dielectric constant, elastic constants, and the ''clamped-ions'' piezoelectric constant. Nonlinear effects on all of them are considered. Our major result is that piezoelectricity is accurately linear over a wide range of volume-conserving strains, while it displays strong nonlinearity whenever the strain is not volume conserving. This finding implies that the observed nonlinear effects can be accurately accounted for by the linear piezoelectric response of the cubic system at the strained volume.