Document Type

Dissertation

Date of Award

2022

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

First Advisor

Dongming Mei

Abstract

High-purity germanium (HPGe) detector has an excellent energy resolution and low-energy detection threshold ideal for searching rare-event physics such as dark matter and neutrinoless double beta decay searches. Understanding the electrical contact properties and the Ge detector properties is key to enhancing the use of Ge detectors for a wide range of applications. Amorphous Ge (a-Ge) is one of the passivation materials used to passivate Ge detectors, which also provides the barrier height to the charge injection. Several a-Ge contact Ge detectors were fabricated and tested at the University of South Dakota (USD) and Max-Planck-Institut (MPI) für Physik in Munich in a different setup. It was also found that a-Ge contacts can survive multiple thermal cycling without any sign of deterioration in the detector performance when directly immersed in cryogenic liquids. The Gaussian distribution model developed by Werner and Guttler is used to characterize the inhomogeneity of the interface made by a-Ge and crystalline Ge. The inhomogeneity leads to the fluctuation in the barrier height with respect to the temperature. Further work is done on characterizing the Ge detector at the temperature range ~ 5 - 80 K. It was found that the free charge carriers in a Ge detector remain constant on average for the temperature range 11 - 80 K, further lowering the temperature below 11 K, impurities in the Ge start to freeze-out and the detector behaves like an ideal capacitor at less than ~ 6.4 K. It was also found that the holes (electrons) in p-type (n-type) Ge are more severely trapped than the electrons (holes) in p-type (n-type) Ge detector at around liquid helium temperature.

Subject Categories

Condensed Matter Physics | Nuclear | Other Physics

Keywords

amorphous germanium, charge-trapping, germanium detector, impurities freeze-out, inhomogeneity, rare-event searches

Number of Pages

135

Publisher

University of South Dakota

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