University thesis:
Dissertation, Universität Freiburg, 2021
Footnote:
Description:
Abstract: This work is a contribution to the development of radiation hard silicon detectors for the application in high energy physics experiments.<br>First, a study was carried out to investigate radiation induced effects in Low Gain Avalanche Detectors (LGADs) and how these effects change with annealing of the devices. For this, two LGADs were irradiated with 24 GeV/c-protons to a fluence of 10 14 n eq /cm 2 . The sensors were then characterized as a function of annealing time by measurements of the leakage current and the capacitance and by<br>measurements using the Transient Current Technique (TCT). An initial decrease of gain, as well as a reduction of the gain layer depletion voltage was observed after irradiation. No further change of gain with annealing was observed. The decrease of gain with irradiation and the change of the gain layer depletion voltage was attributed to a deactivation of the gain layer, mainly due to the acceptor removal<br>effect. A change of the charge collection onset voltage for top-TCT measurements with annealing time was explained by a build-up of charge at the backside, which changes the electric field configuration in the sensor. This effect vanished after reverse annealing. In addition, a tabletop TCT-setup, using two-photon absorption (TPA-TCT), was constructed and commissioned. TPA-TCT is a novel technique for sensor characterization with improved spatial resolution in 3D. Strong focusing of laser light with sub-bandgap photon energy is used to create free charge carriers in silicon only at the focal point of the beam. Measurements performed so far were<br>carried out at dedicated laser laboratories. The setup, developed in the course of this work, serves as a prototype for other research institutes. All components of the setup, including free-space laser optics, the electrical and mechanical devices, were acquired and installed. First tests revealed shortcomings of the laser source, which were addressed by the manufacturer in an upgrade of the source. The setup<br>is now operational and initial measurements were successful. A description and characterization of the setup, as well as the results of first measurements are presented