Charge collection and noise analysis of heavily irradiated silicon detectors

Measurements performed on high-resistivity silicon detectors irradiated with proton and neutron fluences, up to 3.5×10¹⁴ p/cm², and 4.0×10¹⁵ n/cm² respectively, are presented. The charge collection efficiency (CCE) and the output noise of the devices have been measured to carry out a detector performance study after irradiation. The CCE is found to slowly decrease for fluences increasing up to approximately 1.8×10¹⁴ p/cm². For higher particle fluences, the device inefficiency increases rapidly because full depletion could not be reached (up to 75% for the highest fluence: 4×10¹⁵ n/cm ²). A complete analysis of the noise of the irradiated devices has been carried out assuming a simple model which correlates the main noise sources to the fluence and the leakage current. A linear dependence of the square of the noise amplitude on the fluence has been observed: a value of the leakage current damage constant has been found to be in good agreement with the values reported in literature, obtained with current-voltage (IV) analysis. An extension of the noise analysis is carried out considering the detectors irradiated with very high fluences, up to 4×10¹⁵ n/cm²