Growth and structure evaluation of strain-relaxed Ge1−xSnxbuffer layers grown on various types of substrates

We have performed growth and structure evaluation of strain-relaxed Ge 1− x Sn x buffer layers grown on Si(0 0 1), virtual Ge(0 0 1) and bulk Ge(0 0 1) substrates. In the case of Si(0 0 1), amorphous Ge 1− x Sn x phases are partially formed as well as many threading dislocations in Ge 0.98 Sn 0.02 layers. Employing virtual Ge substrates to reduce the lattice mismatch at the interface leads to epitaxial Ge 0.978 Sn 0.022 layers with a flat surface. Most of threading dislocations in the Ge 0.978 Sn 0.022 layer comes from pre-existing ones in the virtual Ge substrate and propagates laterally, leaving misfit segments at the Ge 0.978 Sn 0.022 /virtual Ge interface, after post-deposition annealing (PDA). This simultaneously results in the reduction of threading dislocation density and the promotion of strain relaxation. In the case of bulk Ge(0 0 1), although low threading dislocation density can be achieved, less than 10 6 cm −2 , the film exhibits surface undulation and a lesser degree of strain relaxation even after PDA.