This master’s thesis presents a study on the effective inter-pad distance of low gain avalanche detector (LGAD) prototypes for the High Granularity Timing Detector at the ATLAS experiment. Prototypes from two producers were investigated. LGADs are the technology of choice for track timing detectors at the upgraded High-Luminosity Large Hadron Collider due to their superior timing resolution provided by the additional highly doped layer called the gain layer. Measurements presented in this work focus on the inter-pad region of the prototypes. Effects of radiation damage on the effective inter-pad distance have been studied by measuring samples irradiated with reactor neutrons to an equivalent fluence of $2,5 \cdot 10^{15} \, 1 \, \mathrm{MeV} n_{eq} \, \mathrm{cm^{-2}}$. Basic properties of the detectors were extracted by measuring the C-V and I-V characteristics. The dependence of the effective inter-pad distance on bias voltage and fluence was systematically measured with the Transient Current Technique using laser light of different wavelengths. Bending of the electric field lines at the edges of the electrodes was found to be the reason for the difference between measured and nominal inter-pad distances. The effective inter-pad distances were also simulated and compared to the measurements.
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