STATISTICS OF CARRIER RECOMBINATION AND TRAPPING AND ENERGY RESOLUTION IN SILICON JUNCTION DETECTORS

The problem of recombination and trapping of excess charge carriers in nuclear radiation detectors has been discussed. Firstly, a physical model based on these processes is developed to elucidate the limitations on energy resolution. Ir is suggested that recombination and trapping of charge carriers via recombination centers cause random fluctuation of carrier densities in the free bands and hence energy-line broadening. Corresponding to these processes two sources of noise have been traced viz. generation-recombination noise and trapping-detrapping noise. Then, the details and conditions under which these noises come into play have been worked out specifically for diffused silicon p-n junction detectors. It is shown that with a high-pass filter generation-recombination noise decreases rapidly with decreasing temperature whereas trapping-detrapping noise changes but little. After considering these sources of noise charge collection efficiency is investigated in the presence of preferential carrier trapping. Under these conditions it is shown that charge collection efficiency actually improves when the p-n junction detectors are operated at reduced temperatures. However, preferential trapping can bring in polarization effects and cause injection of spurious charge. Finally, criteria for obtaining trap-free behaviour of the detectors are given. It is indicated that a p-n junction diffused detector prepared from 300 ohm·cm p-Si should show trap-free behaviour at any temperature. © 1969.