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

6Inuence of Bias VoltageIt was a general belief that bias voltage does not aect creation or time developmentof radiation induced defects in silicon. It also seemed consistent with the rst irradiationsmade in the scope of this work (diodes SA and P0). As we understand so far thereasons that the bias eect was not seen were in only partially biasing the samples andfrequent time intervals with no bias at all. This must have reduced the eect of the biassuciently to attribute the remaining dierence between biased and unbiased samples toother parameters (dosimetry, measurement errors etc). Thus it was rather late before thiseect was observed and systematically studied. This reects in the results of previouschapters, where most of the samples were only partially biased. Parameters obtained bythose measurements are thus a combination of those for biased and those for unbiasedsamples.6.1 Inuence on Neff6.1.1 Time Development of Unbiased SamplesTo study reverse annealing of unbiased samples a pair of oat-zone Micron planar processed11cm 2 diodes, with initial FDV of about 18 V, were irradiated and stored withoutbias. Diodes were irradiated in parallel, to a uence of 4:1 10 13 n/cm 2 1 MeV neutronequivalent (irradiation ux 1:8 10 9 n/cm 2 s). After 1 day at room temperature, timedevelopment was accelerated by heating to 60 C. Time development together with a rstorder (eq. 2.57) and a second order (eq. 2.61) t for both diodes is shown in g. 6.1.Results of the ts are given in table 6.1.Comparison of the ts with measured data (g. 6.1) shows better agreement for thesecond order expression. This is conrmed by an about 5 times lower 2 /ndf for the secondorder ansatz (table 6.1). Since the complete volume of both samples was undepleted during89