PIEZOREFLECTIVITY INVESTIGATION OF CDTE(CD,ZN)TE HETEROSTRUCTURES

The deformation potentials of CdTe are such that a (001) or (111) in-plane biaxial strain strongly shifts the energies of the light hole states and leaves nearly unchanged the heavy hole states. As a consequence, in strained CdTe-based heterostructures, from piezoreflectivity measurements combined with first-order derivatives of the reflectivity structures, we identify in terms of heavy and light hole exciton's all features associated with optically active layers (epilayers, substrates, buffer layers, quantum wells and/or superlattices). This appears of crucial relevance in the CdTe/(Cd,Zn)Te heterostructures (with a zinc composition of less than 0.15) because the lattice mismatch-induced splitting, the electron-hole Coulomb interaction and the valence band offset have the same order of magnitude. This produces a complex situation relating to the electronic states of the valence band. From the analysis of our experimental data via the envelope function formalism, including the specific strain effects, we find (i) new shear deformation potentials of CdTe; (ii) unambiguous identification of the character (heavy or light, type I or II) of excitonic ground states, in CdTe/(Cd,Zn)Te quantum wells and strained-layer superlattices; (iii) an accurate value of the chemical band offset between CdTe and (Cd,Zn)Te; (iv) finally, period dependence of the heavy and light hole exciton binding energies.