Bias-dependent annealing of radiation damage in neutron-irradiated silicon p+-n-n+ diodes

Abstract

Silicon pad diodes fabricated on n type substrates were irradiated with fast neutrons from the TRIGA reactor facility to uences around 510 13 n=cm 2 . Annealing of radiation-induced defects was monitored via the full depletion voltage (FDV) obtained from C V measurements, both during and after irradiation. As much a s 5 0 % dierence in FDV was observed to appear between biased and unbiased diodes in a few hours after irradiation, with the biased diodes having the higher value. The FDV dierence persists through later stages of annealing and reverse annealing. Upon switching o the bias voltage, the dierence in FDV diminishes within days at room temperature. Observation of dierent eective dopant concentrations within the same detector in regions with and without electric eld provides further evidence for bias-dependent annealing. No bias eect is seen on the reverse-current annealing.The change of eective impurity concentration in silicon, caused by irradiation with fast heavy particles (protons,pions, neutrons), results in a change of the full depletion voltage. Another eect of irradiation is an increase of the leakage current related to the introduction of defects with energy levels near mid-gap. The damage is found to scale with the non-ionizing energy loss (NIEL) of particles. Silicon will beused as the sensing medium for charged particles in trackers and calorimeters at experiments being constructed for the LHC. The increase of full depletion voltage together with the increase of leakage current could result in an electric breakdown, thermal runaway and unacceptable increase in parallel noise, setting a limit on usage of silicon detectors for these applications.A lot of measurements have been performed in order to predict the level of radiation damage in silicon at LHC experiments. An increase of eective acceptor concentration has been observed during irradiations. This increase,

Comparison of radiation damage in silicon induced by proton and neutron irradiation

“…If we calculate the ratio of factors of reactor neutrons to that of 24-GeV/ protons, we get . This ratio is in agreement with the NIEL factor ratio of [4], [5], and [10], as stated above.…”

“…1 The theoretical "relative hardness" of the 24-GeV/ protons, which is the ratio of the NIEL factors of the 24-GeV/ protons to that of 1-MeV neutrons, can be roughly extrapolated to a value -from [4] or to a value -from [5] and [6]. The neutrons in the nuclear reactor core have a wide energy spectrum ranging from thermal to around 10 MeV, with a total relative hardness factor of 0.88 [10].…”

Performance of 3-D architecture silicon sensors after intense proton irradiation

“…No equipment was available, at the time of these runs, to apply a voltage bias to the detectors. Some recent work indicates that biased detectors may have a depletion voltage increase double that of unbiased ones [40], [41]. Both neutrons and pions showed closely similar effects.…”