Properties and mechanism analysis of metal/Ge ohmic contact

Large contact resistance due to Fermi level pinning effect at the interface between metal and n-type Ge strongly restricts the performance of Ge device on Si substrate. In this paper, the contacts of metal Al and Ni with n-type Ge and p-type Ge epitaxial layers grown by UHV/CVD are comparatively studied. It is found that the contact of NiGe/n-Ge is better than that of Al/n-Ge at the same dopant concentration. When the concentration of P is 21019 cm-3, the ohmic contact of NiGe/n-Ge with c down to 1.4310-5 cm2 is demomstrated, which is about one order of magnitude lower than that of Al/n-Ge contact. The specific contact resistance of NiGe/p-Ge is 1.6810-5 cm2 when the B concentration is 4.21018 cm-3, corresponding to that of Al/p-Ge. Compared with Al/n-Ge contact, P segregation at the interface between NiGe and Ge, rather than lowering Schottky barrier height, is the main reseaon for achieving the low specific contact resistance. NiGe/Ge contact should be a good choice for contact electrode for Ge devices at present.