The Crystalline Structure of Thin Bismuth Layers Grown on Silicon (111) Substrates

Abstract

Bismuth films with thicknesses between 6 and ∼30 nm were grown on Si (111) substrate by molecular beam epitaxy (MBE). Two main phases of bismuth — (Formula presented.) -Bi and (Formula presented.) -Bi — were identified from high-resolution X-ray diffraction (XRD) measurements. The crystal structure dependencies on the layer thicknesses of these films were analyzed. (Formula presented.) -Bi layers were epitaxial and homogenous in lateral regions that are greater than 200 nm despite the layer thickness. Further, an increase in in-plane 2 (Formula presented.) values showed the biaxial compressive strain. For comparison, (Formula presented.) -Bi layers are misoriented in six in-plane directions and have (Formula presented.) -Bi inserts in thicker layers. That leads to smaller (about 60 nm) lateral crystallites which are compressively strained in all three directions. Raman measurement confirmed the XRD results. The blue-sift of Raman signals compared with bulk Bi crystals occurs due to the phonon confinement effect, which is larger in the thinnest (Formula presented.) -Bi layers due to higher compression.