Local uniaxial tensile deformation of germanium up to the 4% threshold by epitaxial nanostructures

Germanium is known to become a direct band gap material when subject to a biaxial tensile strain of 2% or to a uniaxial tensile strain of 4%. In this work we demonstrate that the latter condition can be obtained by exploiting suitable SiGe nanostructures lithographycally defined on top of a Ge film. Such unprecedented strain value is caused by the perimetral elastic forces exerted on the film by the nanostructures, in their attempt to recover their bulk lattice parameter. These findings might lead to the realization of strained-Ge integrated emitters with unprecedented properties, while being compatible with current silicon technology.