  Low Gain Avalanche Detectors(LGADs) is one of the candidate sensing
technologies for future 4D-tracking applications and recently have been
qualified to be used in the ATLAS and CMS timing detectors for the CERN High
Luminosity Large Hadron Collider upgrade.LGADs can achieve an excellent timing
performance by the presence of an internal gain that improves the
signal-to-noise ratio leading to a better time resolution. These detectors are
designed to exhibit a moderate gain with an increase of the reverse bias
voltage. The value of the gain strongly depends on the temperature. Thus, these
two values must be kept under control in the experiments to maintain the gain
within the required values. A reduction in the reverse bias or an increase in
the temperature will reduce the gain significantly. In this paper, a mechanism
for gain suppression in LGADs is going to be presented. It was observed, that
the gain measured in these devices depends on the charge density projected into
the gain layer, generated by a laser or a charged particle in their bulk.
Measurements performed with different detectors showed that ionizing processes
that induce more charge density in the detector bulk lead to a decrease in the
detector's measured gain. Measurements conducted with IR-laser and Sr-90 in the
lab, modifying the charge density generated in the detector bulk, confirmed
this mechanism and will be presented here.
