Charged Defects in Germanium: A First-Principles Study

High-purity Germanium (Ge) detectors have been proven to be the best among the current technologies for the detection of particle signatures in double-beta decay due to their excellent energy resolution and lowest background signal. However, large Ge detectors are prone to charge trapping (CT) phenomena due to the presence of defects and impurities in crystalline Ge, resulting in significant energy resolution degradation. It is therefore imperative to identify such defects and eliminate them during the Ge detector production process. In this work, we employ Density Functional Theory and beyond to study the structural and electronic properties of suspicious charged defects (vacancy, substitutional, and interstitial) in Ge. Our preliminary results show that the n-type defects (P, As, Sb) have lower formation energies compared to the vacancy and interstitial, and their charge transtition level lie closer to the conduction band of Ge. Our results are important for identifying defects, thus may make a significant contribution in developing mitigation strategies to improve the performance of Ge detectors.