FREQUENCY-DEPENDENCE OF AC CONDUCTANCE OF NEUTRON-IRRADIATED SILICON DETECTORS TO FLUENCES UP TO 10(16)N CM(2)/

The dependence of the c onductance (G) and capacitance (C) of the admi ttance (Y = G + jB) as a function of circular frequency (omega), tempe rature (T) and applied reverse bias (V) of neutron irradiated silicon detectors, at neutron fluences (Phi) of up to similar to 10(16) n/cm(2 ), were studied. Significant changes in the characteristics of the dep endence of G and C on omega, T, and V, due to Phi, were found. For low fluences (Phi < 10(13) n/cm(2)) the values of G depend quadratically on omega at T > 150 K. For lower temperatures (T less than or equal to 150 K) a tendency of saturation of G as a function of omega(G similar to omega(m), m < 2) appears. For constant omega, Phi, and T, the valu e of G decreases with increasing V. The capacitance for the same value s of Phi(<10(13) n/cm(2)) decreases with increasing V and Phi. This be havior of G and C as a function of omega, T, V and Phi, is explained u sing an equivalent electrical model. For higher irradiation (10(13) le ss than or equal to Phi 6.5 x 10(15) n/cm(2)), the equivalent electric al model does not fit any more the experimentally observed characteris tics of G and C as a function of omega, V, T(less than or equal to 270 K), Phi(less than or equal to 10(13) n/cm(2)). This was explained as due to the creation of strongly damaged silicon by high fluence with o ther electrical properties than the non-or low-irradiated silicon. The equivalent resistance of the new type of silicon is assumed to be con nected in series with the resistance corresponding to the structure of non-or low-irradiated ones and, its equivalent thickness, increases w ith increasing Phi. On the basis of this model the behavior of the str ongly irradiated detector (Phi > 10(13) n/cm(2)) may be understood. (C ) 1998 Elsevier Science B.V.