Epitaxial synthesis of hybrid heterostructures based on calcium–barium fluoride solid solutions on silicon substrates and X-ray diffraction studies of their lattice parameters

Abstract

It is known that Pb_1−ySn_yTe materials are attractive for studies in the area of topological insulators when y > 0.3–0.4. In this work, a family of heterostructures based on a Pb_1−ySn_yTe/BaF₂/Ca_1−xBa_xF₂/CaF₂/Si(111) epitaxial system was grown via a molecular beam epitaxy method. The lattice parameter values of each sub-layer were determined, and the nature of the elastic strains leading to the mutual inter-influence of sub-layers was estimated. The use of a Ca_1−xBa_xF₂ solid solution enabled a smoother transition in the lattice constant and a reduction in tensile and compressive strains between the sub-layers compared to a heterostructure without the use of this solid solution. Thus, it was shown that the use of a metamorphic buffer layer, including a Ca_1−xBa_xF₂ solid solution, improved the quality of all interfaces within the combined buffer layer by reducing the layer strain. It was observed that the barium fluoride sub-layer exhibited a smaller mismatch in lattice parameters under compressive strain than under tensile strain, which occurred in the absence of a solid solution layer. For CaF₂ growth, a layer-by-layer Frank–van der Merwe growth mechanism was demonstrated, while for Ca_1−xBa_xF₂ growth, the Stranski–Krastanov growth mechanism predominated, and for BaF₂ growth, the Volmer–Weber island growth mechanism was observed. It was confirmed that the CaF₂ lattice rotated at 180° relative to the silicon lattice during high-temperature growth, with subsequent retention of the solid solution and barium fluoride orientations.