Observation of time-dependent internal charge amplification in a planar germanium detector at cryogenic temperature

For the first time, time-dependent internal charge amplification through impact ionization has been observed in a planar germanium (Ge) detector operated at cryogenic temperature. In time period of 30 and 45 minutes after applying bias voltage, energy corresponding to baseline 59.54 keV $\gamma$ rays from $^{241}$Am source is amplified for short then decreases back baseline. The depends strongly on applied positive voltage with drifting holes across detector. No such phenomenon visible electrons We find that dictated by charged states, which strong correlation impurity level electric field. analyze dominant physics mechanisms are responsible creation states. Our analysis suggests appropriate Ge can enhance yield states achieve extremely low-energy detection threshold ($<$ 10 meV) MeV-scale dark matter searches if be stabilized.