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

We have grown a tensile-strained Ge layer on a strain-relaxed compositionally step-graded Ge1 − xSnx buffer layer using virtual Ge substrates. The degree of strain relaxation along [110] direction of the top Ge0.945Sn0.055 buffer layer is achieved up to 85% and the resultant (110) lattice spacing of the Ge0.945Sn0.055 buffer layer is estimated to be 0.4028 nm. A pseudomorphic Ge layer is successfully grown on the Ge0.945Sn0.055 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 Ge1 − xSnx buffer layer directly grown on Si(001) substrates.