Epitaxial relations, crystalline structure and defects in the double Si(111)/hR6 CaSi₂/Si(111) heterostructures

Abstract

The morphology and crystalline structure of Si(111)/CaSi₂/Si(111) double heterostructures (DHS) formed by the Ca reactive deposition epitaxy on the Si(111)7 × 7 surface and Si overgrowth at 500 °C have been studied by atomic force microscopy and transmission electron microscopy. It was established that stressed CaSi₂ layers with stacking faults in (001)CaSi₂ plane and {111}-twinned epitaxial or polycrystalline Si layers were grown. Epitaxial Si layers while had orientation parallel to the Si(111) substrate surface. CaSi₂[100]||Si[] and CaSi₂(001)||Si(111) epitaxial relations were conserved for all grown DHS and they did not depend from the silicon growth mode: molecular beam epitaxy (MBE) or solid phase epitaxy (SPE). The CaSi₂ layer in (001)CaSi₂ plane has a hR6 modification and parameters: a = 0.393 ± 0.002 nm; c = 3.09 ± 0.18 nm at SPE Si growth mode. But some another parameters: a = 0.382 ± 0.002 nm; c = 3.09 ± 0.18 nm were observed at MBE Si growth mode. The compression in c parameter on near 1.07–1.14% as compared with c-value (3.06 nm) for tabular CaSi₂ data is established fact for both HDS. The observed differences in a parameter +1.85% (at SPE mode) and −1.08% (at MBE mode) is not clear now, and demands additional experiments. Some assumptions about mechanisms of occurrence and distribution of compressions and stretching in the CaSi₂ lattice were made.