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

Studies of annealing at temperatures up to 450 degrees 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/cm2 was already improved at 5 min of annealing at 250 degrees C. Isochronal annealing for 30 min in 50 degrees C steps between 300 degrees C and 450 degrees C showed that the largest beneficial effect of annealing is at around 350 degrees C. Another set of devices was annealed for 60 min at 350 degrees 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 similar to 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.