  We experimentally study III-V/Ge heterostructure and demonstrate InGaAs
hetero-contacts to n-Ge with a wide range of In % and achieve low contact
resistivity ($\rho_C$) of $5\times10^{-8} \Omega\cdot cm^2$ for Ge doping of $3
\times 10^{19} cm^{-3}$. This results from re-directing the charge neutrality
level (CNL) near the conduction band and benefiting from low effective mass for
high electron transmission. For the first time, we observe that the
heterointerface presents no temperature dependence despite the two different
conduction minimum valley locations of III-V ($\Gamma$-valley) and Ge
(L-valley), which potentially stems from elastic trap-assisted tunneling
through defect states at the interface generated by dislocations. The
hetero-interface plays a dominant role in the overall $\rho_C$ below $\approx 1
\times 10^{-7} \Omega \cdot cm^2$, which can be further improved with large
active dopant concentration in Ge by co-doping.

Materials Science;Mesoscale and Nanoscale Physics