Thermal-mismatch strain relaxation mechanisms in heteroepitaxial lead chalcogenide layers on Si substrates

Narrow-gap IV-VI lead chalcogenide layers grown on Si substrates with the aid of an intermediate CaF 2 /BaF 2 buffer relax the thermal-mismatch-induced strain by misfit dislocations which glide on the primary (100) glide planes inclined 54.7 degrees with respect to the (111) surface. Macroscopic strain measurements show near complete mismatch strain relaxation down to cryogenic temperatures even after multiple cycling for binary PbSe, while ternary PbSe 1-x Te x (x=0.4) strains elastically below room temperature. The morphology of the resulting dislocation steps is revealed by scanning tunnelling microscopy for the IV-VIs and atomic force microscopy for the fluoride buffer, and the number of dislocation step lines agrees with the calculated thermal strain relaxation.