Temperature dependence of photocurrents produced by x and gamma rays in silicon radiation detectors

Th e te mpe rat ure depend e nce of d c photoc urre nts produ ced b y x a nd ga mma rays in sili co n radia tion detec tors of the n-p, pin, and s urfa ce barrie r type was in vestigated in a temperature range between 20 and 50C. Photodiode photoc urre nt.s, assumed as bein g e qua l to th e generated cu rre nts I g, s howe d a positive temperature depe nd e nce in a ll de tec tors inves ti ga te d. Th eir temperature coeffi c ie nt at 25C varied between + 0.004 per C and + 0.002 per 0C. Th e te mpe rature dependence of s hortcirc uit c urre nt s Is, meas ure d by a co mpe nsa tion method , was pos itive a nd nea rl y lin ear for np type d etectors but nonlinear and nega tiv e for pin and s urface barrie r type detectors. It is sh ow n , th at th is diffe re nt behavior of in dividua l de tec tors is du e to th e influ e nce of th e s tro ngly temperature de pe nd e nt junc tion c urre nt Ij whi c h und er the s hortcirc uit mod e is dra in e d off th e ge nerat.ed c urre nt I". The junc ti on c urre nt is a fun c t.i on of the int e rna l se ri es res is tance Rs and th e junctio n res istan ce Rj of th e irradi a t.ed d etector (/j= I,e R.,/Rj ). Wit.h in c reas in g res is ta nce ra tio R.,/Rj, the c urren t ratI o 1;ll y inc reases a nd th e te ml)e rature coeffi cie nt a se of th e s hortcirc uit c urre nt dec reases. Temperature coeffi cie nts (aseL-, meas ured in th e d iffere nt det ectors a t 25C and a c urre nt de ns it y 6 X 10-7 A/cm' d ecreased with in c reas in g res is tance rati o from + 0.004 per C to -0.005 per dc. Res is ta nce ratios R .. /Rj of th e d ete ctors inves tiga t.e d ran ged be twee n 0.01 and 0. 24 approximate ly. Thus , (C< sel" meas ured in a n individual detec tor ca n be changed by c ha ngin g it s effective series resis tan ce. A de crease of (asel,.; with in c reasin g Ise wa s obse rv ed in de tectors with la rger resi s ta nce rati os. This was appar e ntl y du e to th e voltage de pe nd e nce of Rj a t hi ghe r junc tion voltages produced by la rge r short-c irc uit c urren ts.