Thesis defense of Mareike Wagner
- Defense
In high energy physics experiments new conditions require continuously improved sensors and modules for particle detection. The REINER pixel modules were developed featuring different pixel designs to improve the sensor performance, especially after irradiation. The results for laboratory and test beam measurements for several of these modules are presented in this thesis.
In total nine modules have been irradiated with protons and neutrons to study their performance at the end-of-lifetime of a sensor in the ATLAS Pixel Detector and investigate the intended charge multiplication effect. While all non-irradiated pixel designs showed similar charge collection and hit detection efficiency results, their behavior differs after irradiation. The irradiated standard pixel design measured highest hit detection efficiencies at low bias voltages except for one highly neutron irradiated module (5 × 10^15 neq/cm²). For this module, a pixel design with narrowed n+-implantation (V5) reached significantly higher particle detection efficiencies at low bias voltages. The results of ensuing annealing studies of a different highly neutron irradiated module showed that the observed higher particle detection efficiencies for pixel design V5 are an annealing effect: An increase in generated charge and hit detection efficiency was observed for this design after long annealing times.
In addition, an existing TCT measurement setup was modified in this thesis to measure the laser induced charge collection efficiency in the laboratory with subpixel resolution. First promising results of this setup are consistent with in-pixel maps from test beam measurements: The increased charge collection and hit detection efficiency of pixel design V5 after irradiation and annealing are likely caused by electric field strength maxima at the corners and edges of the n+-implantation. This higher electric field broadens the depletion zone and a charge multiplication effect is achieved.