Influence of temperature on the I-V and C-V characteristics of Si detectors irradiated at high fluences

Measurements of I-V and C-V characteristics of non-irradiated and irradiated silicon detectors, at fluences 1.2 × 1013n/cm2 ≤ Φ ≤ 5.9 × 1014n/cm2, were made in forward and reverse bias at low temperatures. An abrupt increase of the value of forward current was found at given bias voltages VS. This value increases with increasing values of Φ. The capacitance was measured at reverse bias VR, at ω = 10 kHz, and at temperatures 10 K ≤ T ≤ 200 K. The capacitance is a function of applied reverse bias, but for a given critical temperature Tc, it does not change any more and remains constant for all applied values of VR. This value of Tc depends on Φ. For increasing Φ, the critical temperature Tc increases, e.g. for a non-irradiated sample, Tc = 20 K and for a sample irradiated at Φ = 5.9 × 1014n/cm2, Tc = 150 K. The observed phenomena can be explained assuming a freeze-out of free carriers at very low T, and space-charge-limited current (SCLC) for the very low concentration of majority carriers.