Gain recovery in heavily Irradiated Low Gain Avalanche Detectors by high temperature annealing

Studies of annealing at temperatures up to 450 °C with Low Gain Avalanche Detectors (LGAD) irradiated with neutrons are described. It was found that the performance of LGADs irradiated with 1.5e15 n/cm$^2$ was already improved at 5 min of annealing at 250 °C. Isochronal annealing for 30 min in 50 °C steps between 300 °C and 450 °C showed that the largest beneficial effect of annealing is at around 350 °C. Another set of devices was annealed for 60 min at 350 °C and this annealing significantly increased depletion voltage of the gain layer (V$_{gl}$). The effect is equivalent to reducing the effective acceptor removal constant by a factor of ∼ 4. Increase of V$_{gl}$ is the consequence of increased effective space charge in the gain layer caused by formation of electrically active defects or re-activation of interstitial boron atoms.