Direct detection of MeV-scale dark matter utilizing germanium internal amplification for the charge created by the ionization of impurities

Light, MeV-scale dark matter (DM) is an exciting DM candidate that is undetectable by current experiments. A germanium (Ge) detector utilizing internal charge amplification for the charge carriers created by the ionization of impurities is a promising new technology with experimental sensitivity for detecting MeV-scale DM. We analyze the physics mechanisms of the signal formation, charge creation, charge internal amplification, and the projected sensitivity for directly detecting MeV-scale DM particles. We present a design for a novel Ge detector at helium temperature ($$\sim $$ 4 K) enabling ionization of impurities from DM impacts. With large localized E-fields, the ionized excitations can be accelerated to kinetic energies larger than the Ge bandgap at which point they can create additional electron–hole pairs, producing intrinsic amplification to achieve an ultra-low energy threshold of $$\sim $$ 0.1 eV for detecting low-mass DM particles in the MeV scale. Correspondingly, such a Ge detector with 1 kg-year exposure will have high sensitivity to a DM-nucleon cross section of $$\sim $$ 5 $$\times $$ 10$$^{-45}$$ cm$$^{2}$$ at a DM mass of $$\sim $$ 10 MeV/c$$^{2}$$ and a DM-electron cross section of $$\sim $$ 5 $$\times $$ 10$$^{-46}$$ cm$$^{2}$$ at a DM mass of $$\sim $$ 1 MeV/c$$^2$$