  Electrical injection of spin-polarized electrons into a semiconductor, large
spin diffusion length, and an integration friendly platform are desirable
ingredients for spin-based devices. Here we demonstrate lateral spin injection
and detection in germanium nanowires, by using ferromagnetic metal contacts and
tunnel barriers for contact resistance engineering. Using data measured from
over 80 samples, we map out the contact resistance window for which lateral
spin transport is observed, manifestly showing the conductivity matching
required for spin injection. Our analysis, based on the spin diffusion theory,
indicates that the spin diffusion length is larger than 100 {\mu}m in germanium
nanowires at 4.2 K.
