Frequency dependence of A.C. conductance of non-irradiated and neutron irradiated silicon detectors

The admittance-Y (real and imaginary) as a function of frequency (ω) and temperature (T) of silicon detectors, non-irradiated and neutron irradiated, were studied. An electric circuit model of Y(ω) was calculated. The experimentally measured data for real part of admittance G as a function of ω have shown a quadratic dependence G ∝ ω2, for temperatures T ≥ 40 K. This experimental dependence was the same as resulted from the calculations based on the electric circuit model for the region of values T where G was proportional to the resistivity of the silicon detector (ρ). For temperatures T < 40 K, the A.C. conductance G ∝ ωn (n < 2). It was shown that the value of ω, where this dependence appears, decreases with decreasing T. Due to the increase of mobility of free carriers at low temperatures where G ∝ ρ (50 ≤ T ≤ 270 K), the value of G decreased with decreasing T (G ∝ Ta, a = 2.3 for 170 ≤ T ≤ 270 K and a = 1.8 for 50 ≤ T ≤ 150 K). At T ≤ 20 K, due to the process of freeze-out of free carriers, the value G remains practically independent on ω and on further decrease of T. Measurements on neutron irradiated samples at Φ > 1013 n/cm2, have shown important changes in the dependence of G as a function of ω and T. (orig.)