UBC Theses and Dissertations
Characterization study of Si HVeV detectors through analysis of charge spectra Musaab, Al-Bakry
In the pursuit of directly detecting Dark Matter (DM), the SuperCDMS experiment, situated at the SNOLAB facility in Canada, focuses on studying two primary types of detectors for use in the main experiment: iZIP and HV detectors. In this analysis, we examine a specific type of detector known as High Voltage eV-resolution (HVeV) detectors. These detectors are smaller in size and offer superior resolution compared to HV detectors. The HVeV detector consists of high-purity silicon operating at low temperatures and uses the Neganov-Trofimov-Luke (NTL) effect to convert the signals of electron/hole pairs created by energy deposition into detectable phonon energy, which is measured using transition edge sensors on the surfaces of the detector. An integral part of studying HVeV detectors involves investigating the probabilities of Charge Trapping (CT), in which charge carriers are lost without receiving the full NTL amplification, and Impact Ionization (II), in which charge carriers dislodged from impurities in the crystal contribute additional photon energy through the NTL effect. Measurements of a prototype HVeV detector at TRIUMF reveal a CT probability of (12.0 ± 0.2)% and an II probability of (1.4 ± 0.2)%. A notable observation is the strong correlation between the intensity of the calibration LED and both the position of the spectrum peak and the detector resolution. We propose an explanation for this effect: the presence of non-quantized energy deposition due to photons that are absorbed without NTL amplification. We develop a model and provide substantial evidence to support this hypothesis. Lastly, we discuss the implications of this effect on calibration in previous SuperCDMS runs, highlighting the potential consequences it may have.
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