Characterizing a p-type Ge detector operated at cryogenic temperature by measuring the binding energy of cluster dipole states for low-mass dark matter searches*

We have studied the potential application of a p-type Ge detector operated at cryogenic temperature (at 5.2 K) for low-mass dark matter searches. By measuring the binding energies of cluster dipole states as a function of the applied electric field, the detector is operated in two different modes:

The first mode is that the detector is depleted at 77 K and then decreases the temperature to 5.2 K.

The second mode is that the detector is directly cooled down to 5.2 K.

In the two modes, the detector is exposed to an Am-241 source, which emits alphas with an energy of 5.5 MeV. It has been observed that the binding energy of cluster dipole states is lower in the second mode than in the first mode. The binding energy of the cluster dipole states in this p-type Ge detector is found in the range of ~ 4-8 meV. Such a small energy indicated that this detector can be used to study low-mass dark matter.