Epitaxial growth of atomically-sharp GeSn/Ge/GeSn tensile strained (≥1.5 %) quantum well on Si

In a full-group IV integrated semiconductor platform for tensile-strained Ge the direct-band gap can be obtained when the Ge is grown on a lattice-mismatched Ge_0.87Sn_0.13 substrate. The main challenge is to increase the incorporation of Sn in Ge above the ~1at.% equilibrium composition. Major developments were recently achieved in the epitaxial growth of random GeSn alloys with composition above 16at.%. A biaxial tensile strain in a Ge layer up to ~1.5% was demonstrated when growing on a Ge_0.88Sn_0.12 substrate. However, despite the large amount of tensile strain in Ge, no information are available on the abruptness of the Ge-GeSn interface and on the possibility of the subsequent GeSn growth on top.
Here, we discuss the epitaxial growth of a tensile-strained GeSn/Ge/GeSn heterostructure(s-Ge) with sharp interfaces and in-plane biaxial strain above 1.5% grown on lattice-mismatched Ge_0.86Sn_0.14. The sharpness of the Ge/GeSn heterostructure interfaces will be addressed using TEM-EELS and atom probe tomography(APT) measurements. A defect-free s-Ge layer thickness in the 13-1.2nm range is achieved and its pseudomorphic nature will be discussed using STEM and XRD. The s-Ge QW platform is a new versatile platform to investigate LH spin-based qubits and high hole mobility electronics.