Rhombohedral distortion of EuS epitaxial films on Si(111) substrates

Abstract

Films of EuS 8–500 nm thick produced by molecular beam epitaxy on Si(111) at 900°C and 10 -7 Pa exhibit domains with the same orientation as silicon and a larger fraction of 180° twin domains. Because of the thermal mismatch the thin films are distorted rhombohedrally below about 500 °C in such a way that the EuS layer adherent to the silicon adjusts to the thermal expansion of silicon while the axis perpendicular to Si(111) contracts 10–18 times as much, which give rise to a 0.5% increase in volume compared with the volume of EuS single crystals at room temperature. Annealing for several days at 200–300°C in inert gas leads to a decrease in the rhombohedral distortion and an increase in the volume by about 1%, which is caused by an increased number of lattice defects.