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 $10^{\mathrm {{19}}}$ cm $^{-3}$ ) were studied to obtain ohmic contact by forming Yb stanogermanide through $\alpha $ -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 $\alpha $ -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 ( $\Phi _{\mathrm { {BN}}}$ ) of 0.13 eV, a low contact resistivity ( $\rho _{c}$ ) of $3.8\times 10^{-7}~\Omega $ -cm $^{\mathrm { {2}}}$ , and smoother surface roughness. The root cause that explains the phenomenon is the better morphology of the stanogermanide due to the $\alpha $ -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 $\alpha $ -GeSn capping layer empowering the emerging GeSn technology.