Investigation of the electrical conduction mechanisms in P-type amorphous germanium electrical contacts for germanium detectors in searching for rare-event physics

Abstract

For the first time, electrical conduction mechanisms in the disordered material system is experimentally studied for p-type amorphous germanium (a-Ge) used for high-purity Ge detector contacts. The localization length and the hopping parameters in a-Ge are determined using the surface leakage current measured from three high-purity planar Ge detectors. The temperature dependent hopping distance and hopping energy are obtained for a-Ge fabricated as the electrical contact materials for high-purity Ge planar detectors. As a result, we find that the hopping energy in a-Ge increases as temperature increases while the hopping distance in a-Ge decreases as temperature increases. The localization length of a-Ge is on the order of $$2.13^{-0.05}_{+0.07}\mathrm{{A}}^\circ $$ 2 . 13 + 0.07 - 0.05 A ∘ to $$5.07^{-0.83}_{+2.58}\mathrm{{A}}^\circ $$ 5 . 07 + 2.58 - 0.83 A ∘ , depending on the density of states near the Fermi energy level within bandgap. Using these parameters, we predict that the surface leakage current from a Ge detector with a-Ge contacts can be much smaller than one yocto amp (yA) at helium temperature, suitable for rare-event physics searches.

Dipole and Cluster Dipole States of HPGe Detectors at Cryogenic Temperature

“…The state-of-the-art infrastructure at USD for crystal growth and detector development includes a zone refining process for highly purifying commercial ingots, which can be used for crystal growth with the Czochralski method [21][22][23][24] . This enables the USD detector fabrication lab to produce superior homegrown crystals that are utilized for creating p-type (RL) detector with a net impurity concentration of 6.2 × 10 9 /cm 3 and dimensions of 18.8 mm ×17.9 mm×10.7 mm.…”

Development of Low-Threshold Detectors for Low-Mass Dark Matter Searches Using an N-Type Germanium Detector at 5.2 K

“…To ensure optimal electrical performance, an amorphous Ge passivation layer of 600 nm was coated on the surface of the Ge crystal as the electrical contact, effectively blocking surface charges 26,27 . An alpha source ( 241 Am) was positioned near the detector inside a cryostat, and the energy deposition of α particles was measured.…”

Implication of the Temperature-Dependent Charge Barrier Height of Amorphous Germanium Contact Detector in Searching for Rare Event Physics

“…For a high purity p-type Ge detector passivated with a-Ge contacts and the electrodes formed by deposition of Al, if it is negatively biased from the bottom electrode, then the detector starts to deplete from the top and the BLC is primarily dominated by hole injection from the top contacts. Non-zero conductivity of a-Ge also contributes to the SLC influenced by the hopping conduction mechanism [32,33]. The charge collection in a Ge detector is usually carried out with a bias voltage that is a few hundreds volts above the full depletion voltage at which the contribution to the BLC is from both the top and bottom contacts.…”