Tensile strained Ge layers on strain-relaxed Ge1−Sn /virtual Ge substrates

We have grown a tensile-strained Ge layer on a strain-relaxed compositionally step-graded Ge 1-x Sn x buffer layer using virtual Ge substrates. The degree of strain relaxation along [110] direction of the top Ge 0.945 Sn 0.055 buffer layer is achieved up to 85% and the resultant (110) lattice spacing of the Ge 0.945 Sn 0.055 buffer layer is estimated to be 0.4028 nm. A pseudomorphic Ge layer is successfully grown on the Ge 0.945 Sn 0.055 buffer layer, yielding a tensile strain of 0.68% with respect to the (110) lattice spacing of non-strained Ge. This value exceeds those obtained by other methods based on the thermal expansion coefficient difference and strain-relaxed Ge 1-x Sn x buffer layer directly grown on Si(001) substrates.