Growth and structure evaluation of strain-relaxed Ge1-xSnx buffer layers grown on various types of substrates

We have performed growth and structure evaluation of strain-relaxed Ge1-xSnx buffer layers grown on Si(001), virtual Ge(001) and bulk Ge(001) substrates. In the case of Si(001), amorphous Ge1-xSnx phases are partially formed as well as many threading dislocations in Ge0.98Sn0.02 layers. Employing virtual Ge substrates to reduce the lattice mismatch at the interface leads to epitaxial Ge0.978Sn0.022 layers with a flat surface. Most of threading dislocations in the Ge0.978Sn0.022 layer comes from pre-existing ones in the virtual Ge substrate and propagates laterally, leaving misfit segments at the Ge0.978Sn0.022/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(001), although low threading dislocation density can be achieved, less than 106 cm(-2), the film exhibits surface undulation and a lesser degree of strain relaxation even after PDA.