Gain Recovery in Heavily Irradiated Low Gain Avalanche Detectors by High Temperature Annealing

Abstract

Studies of annealing at temperatures up to 450${}^{\circ }$C with LGADs 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 minutes of annealing at 250${}^{\circ }$C. Isochronal annealing for 30 minutes in 50${}^{\circ }$C steps between 300${}^{\circ }$C and 450${}^{\circ }$C showed that the largest beneficial effect of annealing is at around 350${}^{\circ }$C. Another set of devices was annealed for 60 minutes at 350${}^{\circ }$C and this annealing significantly increased V${}_{\mathrm{gl}}$. The effect is equivalent to reducing the effective acceptor removal constant by a factor of $\sim$ 4. Increase of V${}_{\mathrm{gl}}$ 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.