Realization of ideal Ohmic contact to n-Ge: The key roles of Ge-Bi-Te for quasi-van der Waals interface formation

The feasibility of Bi2Te3 as S/D contact for n-Ge has been investigated. After thermal treatment at 400 °C, the formation of Ge1−xBi2+xTe4 (GBT) ternary compound and the realization of the quasi-van der Waals interface are verified from x-ray diffraction analysis and scanning transmission electron microscope observation at the GBT/Ge interface. According to the junction diode characteristics of GBT/Ge, exhibiting Ohmic and rectified behaviors on n-Ge and p-Ge, respectively, it is found that strong Fermi-level pinning commonly observed between metal and n-Ge is mitigated and the Fermi level of Ge moves toward the conduction band side. In addition, the interfacial layer between GBT and Ge even disappeared after 400 °C annealing, leading to ideal Ohmic behavior compared to its Bi2Te3 counterpart. GBT/Ge hetero-structure possesses high thermal stability, which shows tolerance for the back-end-of-the-line process. Through the comprehensive evaluation, GBT shows exceptional potential for achieving low contact resistance in Ge nMOSFETs.