Strain relaxation mechanisms in He⁺-implanted and annealed Si_1-xGe_x layers on Si(001) substrates

Abstract

Strain relaxation in He+-implanted and annealed Si(001)/Si1-xGex heterostructures was investigated using transmission electron microscopy techniques and x-ray diffraction. Depending on the implant conditions, bubbles and/or platelets form below the Si/Si1-xGex interface upon annealing and act as nucleation sources for dislocation loops. The dislocation loops extend to the interface and form a misfit dislocation network there, resulting in relaxation of 30-80% of the strain in layers as thin as 100-300 nm. When bubbles form close to the interface, dislocations nucleate by a climb loop mechanism. When smaller bubbles form deeper in the Si substrate an irregular three-dimensional dislocation network forms below the interface resulting in an irregular misfit dislocation network at the interface. When platelets form deeper in the Si substrate, prismatic punching of dislocation loops is observed and dislocation reactions of misfit dislocations at the interface result in Lomer dislocation formation.