ULTRATHIN PSEUDOMORPHIC LAYERS OF ZNTE IN CDTE/(CD,ZN)TE SUPERLATTICES - A DIRECT OPTICAL PROBE OF THE MIXED-TYPE BAND CONFIGURATION

A range of studies, such as transmission electron microscopy, x-ray diffraction, and optical spectroscopy, applied to a series of CdTe/ZnTe superlattices with ultrathin ZnTe layers, confirmed the ability to grow, in CdTe, ultrathin pseudomorphic layers of ZnTe with limited Zn segregation and of high crystalline and optical quality, at least for layer thicknesses up to a few monolayers. Subsequently, we employed the spatially selective incorporation of monomolecular isoelectronic planes of ZnTe as a perturbative probe of the exciton states in a mixed-type CdTe/(Cd,Zn)Te superlattice. The effect of the ZnTe monolayer as a function of position on the heavy- and light-hole transitions of this system was determined by optical spectroscopy. Our results confirmed experimentally the type-I nature of the heavy-hole excitons and demonstrated the possibility to directly tune the ''indirectness'' of the light-hole exciton, depending on the position of the planar perturbation. Theoretical calculations were found in qualitative agreement with all these results.