Study of radiation damage in silicon detectors for high ... - F9

96 6. Inuence of Bias VoltageFigure 6.6: a) 1/C 2 vs. V plot and b) N eff distribution for the sample I3. Black dots showthe measurements before switching o the bias. Time development after switching the bias ois shown with coloured circles.After prolonged heat treatments, in the rst few days at 5 C a slight decrease(about 5%) in FDV as determined from C/V measurement has been noticed. To avoidthe inuence of this eect, C/V measurements at the late stage of reverse annealing weretaken about a week after transfer to 5 C, when a stable state was reached.6.2 Annealing of the Dierence in NeffAs shown in section 6.1.2 the minimal value of N eff as reached under bias is about twicelarger from the one with no bias applied. In this section results on annealing of thisdierence are presented.Samples D2, UO6, BA2 and BA4 were used to determine time constants of annealingof the dierence between biased and unbiased samples. In all four pairs biased diodes werekept under bias until the end of benecial annealing i.e. until the plateau in N eff wasreached. During this time they had been kept at 15 or 20 C as indicated in table 6.2. After