Electrical and Optical Characterizations of the BNL Low Gain Avalanche Detectors

Low Gain Avalanche Detectors (LGADs) are promising candidates that have been considered for the future applications of 4D-tracking section, which is an important part of the current upgrades of ATLAS and CMS timing detectors to be used in the future operations of the High Luminosity Large Hadron Collider at CERN. This type of sensor features good radiation hardness and fast timing properties featuring a moderate gain in linear-mode operation, thanks to the special engineering of its internal gain layer. In general, different factors like temperature, bias voltage, radiation type and radiation intensity can affect the gain of the detectors. A complete understanding of these effects requires careful analysis through experiments and simulations to find the best compromise among various aspects and enhance their time resolution in the real harsh environments. This paper describes a summary of the experiments done on the gain suppression mechanism of LGAD devices developed at Brookhaven National Laboratory for charged particles detection. Static electrical characterization of the prototypes will also be reported. A fast pulsed IR laser was used in the lab to investigate how the BNL-Detectors’ gains change depending to the input light intensity and the applied reverse bias voltages. Three different ranges of radiation intensities and bias voltages (low, medium and high) were covered during the measurements and finally, a relationship was observed as expected and the results confirmed the fact that the gain values reduce at the higher input radiation intensity and larger reverse bias voltages, due to space charge effects, i.e. the electric field generated by the mobile charges that are crossing the high field region. In addition, a gain value between 60-70 was calculated at the high range voltages close to the device breakdown voltage (380V).