Formation of uniaxial strained Ge via control of dislocation alignment in Si/Ge heterostructures

Uniaxially strained Ge/SiGe heterostructures are fabricated by selective ion implantation technique, where dislocation alignments are highly controlled by the local defect introduction. Firstly, ion-implantation-defects are selectively induced into a Ge substrate, followed by the growth of a SiGe buffer layer. As a result, the SiGe on the implanted region is largely strain-relaxed due to the defects acting as dislocation sources. In contrast, it is demonstrated that anisotropic strain relaxation takes place in the SiGe on the unimplanted region, leading to the uniaxial strained SiGe. A strained Ge layer is pseudomorphically grown on the SiGe buffer and the same strain states are observed for the Ge layer. It is found that misfit dislocations generated at the interface between the SiGe layer and the Ge substrate are aligned along only one direction. These one-directional dislocations are an origin of the uniaxial strain relaxation. Moreover, effects of ion-implantation stripe-pattern widths on the strain states are investigated. With the implanted line width increasing, the anisotropy of the strain in the unimplanted region is enhanced. From these results, it can be said that this technique opens a route to engineer dislocation alignments and anisotropic strain in semiconductor hetero structures toward high performance novel devices.