Growth and characterization of type-II CdTe quantum dots in a ZnCdSe matrix for the use in an intermediate band solar cell*

Intermediate band solar cells (IBSC) have been proposed for being able to overcome the Schockley-Quiesser limit for single junction photovoltaics. The formation of an IB can be accomplished by either Quantum Dots (QDs) or impurities. Here we report on the growth and characterization of CdTe fractional monolayer QDs embedded in a ZnCdSe host matrix grown by a combination of migration enhanced epitaxy (MEE) and molecular beam epitaxy. The proximity of the parameters necessary for an ideal IBSC makes this material system a remarkable candidate for a successful practical device. Some unique attractive features of this material are its binary composition, simplifying growth; the absence of a deleterious interfacial layer, in spite of the lack of common ion; and the presence of strain, which allows for strain engineering of the IB. A superlattice structure of CdTe/ZnCdSe QDs (100 periods) is presented in which the size and the strain of the QDs are analyzed by X-ray diffraction and photoluminescent spectroscopy. Results suggest that thicker QDs are necessary to match the parameters for an ideal IBSC. This can be achieved by adjusting the growth parameters during MEE process.