Document Type
Dissertation
Date of Award
2024
Degree Name
Doctor of Philosophy (PhD)
Department
Physics
First Advisor
Dongming Mei
Abstract
This dissertation explores using high-purity germanium (Ge) crystals for low-mass dark matter (DM) detection, focusing on enhancing crystal quality and identifying key crystal growth parameters. The study assesses the electrical properties of refined Ge materials through Hall Effect measurements and uses machine learning to predict impurity profiles, achieving levels conducive to high-resolution DM detectors. Utilizing a planar Ge detector fabricated at Texas A$\&$M and operated at cryogenic temperatures at the University of Minnesota, the study reveals time-dependent internal charge amplification through impact ionization. Research on charge transport dynamics in a cryogenic p-type Ge detector uncovers evolving charge dynamics and cluster dipole states, enhancing our understanding of charge transport, trapping, and generation processes at mK temperatures. At 40 mK, a zero-field cross-section of $8.45 \times 10^{-11} \pm 4.22 \times 10^{-12}~cm^2$ was observed, significantly higher than that of neutral impurities. The binding energy of cluster dipole states was determined to be $0.034 \pm 0.0017$ meV, lower than ground-state impurities in Ge. Future research directions include investigations into impact ionization rates, thermal effects on dipole states, and trapping cross-sections. The impact ionization of dipole states observed at 40 mK implies a detection threshold of $\le$ 10 meV for MeV-scale DM searches. With such a low-energy threshold, this dissertation projects high sensitivity for MeV-scale dark matter with 1 kg-year exposure, yielding DM-nucleon cross-sections of $2.84 \times 10^{-44}~cm^2$ for DM of mass $80~\text{MeV}/c^2$ and DM-electron cross-sections of $1.90 \times 10^{-46}~cm^2$ for DM of mass $1~\text{MeV}/c^2$.
Subject Categories
Physics
Keywords
Germanium Detectors, low dark matter
Number of Pages
189
Publisher
University of South Dakota
Recommended Citation
Acharya, Pramod, "DEVELOPMENT OF LOW THRESHOLD GERMANIUM DETECTORS FOR THE SEARCH OF LOW MASS DARK MATTER" (2024). Dissertations and Theses. 237.
https://red.library.usd.edu/diss-thesis/237