Ge is of great interest as a candidate channel material for future CMOS devices due to its high intrinsic carrier mobility. To translate this potential into CMOS devices, the source/drain (S/D) junctions are desired to be composed by metal/Ge contacts. However, the Fermi-level pinning impedes the embodiments, by which the formation of a contact with a low electron barrier height (ΦBN) is very difficult. We have found that a TiN/Ge contact deposited by sputtering is useful for a low ΦBN contact. In this paper, we present the electrical properties and interfacial structures of the TiN/Ge contact. Furthermore, we also present the electrical properties and interfacial structures of ZrN/Ge and HfN/Ge contacts, which are in the same group-4 transition-metal nitrides. As an application to the optical device, we present the fabrication and device performance of light emission diodes with lateral TiN/Ge/HfGe structures.