Fermi Level Depinning on n-Epitaxial GeSn by Yb Stanogermanide Formation With Low-Contact Resistivity

Processes for Fermi level (FL) depinning on n-type epitaxial GeSn (N_D of 10¹⁹ cm^-3) were studied to obtain ohmic contact by forming Yb stanogermanide through α-GeSn/Yb/ n-GeSn and SiO₂/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 (_Pc) of 3.8 × 10^-7 Ω-cm², 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.