Abstract
Processes for Fermi level (FL) depinning on n-type epitaxial GeSn (N D of 10 19 cm -3 ) were studied to obtain ohmic contact by forming Yb stanogermanide through α-GeSn/Yb/n-GeSn and SiO 2 /Yb/n-GeSn structure with 500 °C annealing. Compared with Al/n-GeSn contacts which show Schottky conduction, Yb stanogermanide contacts from both structures exhibit ohmic-like behavior, implying the effectiveness to mitigate FL pinning. Nevertheless, the one with α-GeSn capping layer is more desirable, since it reveals superior characteristics to the other counterpart in terms of higher reverse current, a small Schottky barrier height (Φ BN ) of 0.13 eV, a low contact resistivity (ρ c ) of 3.8 × 10 -7 Ω-cm 2 , and smoother surface roughness. The root cause that explains the phenomenon is the better morphology of the stanogermanide due to the α-GeSn capping layer that helps minimize the excess Ge/Sn consumption and nonuniform diffusion from the n-type epitaxial GeSn. By combining these promising properties, Yb stanogermanide formed with α-GeSn capping layer empowering the emerging GeSn technology.