Germanium is one of the most appealing candidate for spintronic applications, thanks to its compatibility with the Si platform, the long electron spin lifetime and the optical properties matching the conventional telecommunication window. Electrical spin injection schemes have always been exploited to generate spin accumulations and pure spin currents in bulk Ge. However, it is well known that ferromagnetic injection or detection blocks can introduce parasitic effects at the metal/semiconductor interface, which are still under debate. Here, we exploit the spin-Hall effect to generate a uniform pure spin current in an epitaxial n-doped Ge channel and we detect the electrically-induced spin accumulation, transverse to the injected charge current density, with polar magneto-optical Kerr microscopy at low temperature. We show that a large spin density up to 400
µm-3 can be achieved at the edges of the Ge channel for a low-voltage applied bias. We find that the spin density linearly decreases toward the center of the Ge bar, due to the large spin diffusion length, and such a decay is much slower than the exponential one observed in III–V semiconductors, allowing very large spin accumulations over a length scale of tens of micrometers. We have also characterized the electrically-induced spin voltage as a function of the applied bias and temperature, revealing that the spin-to-charge conversion in bulk Ge is preserved up to 120 K.