  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$.
