Silicon particle detectors will be used extensively in experiments at the CERN Large Hadron Collider, where unprecedented particle fluences will cause significant atomic displacement damage. We ...present a model of the evolution of defect concentrations and consequent electrical behaviour in “novel” detector materials with various oxygen and carbon impurity concentrations. The divacancy-oxygen (V
2O) defect is identified as the cause of changes in device characteristics during
60Co gamma irradiation. In the case of hadron irradiation, changes in detector doping concentration (
N
eff) are dominated by cluster defects, in particular the divacancy (V
2), which exchange charge directly via a non-Shockley–Read–Hall mechanism. The V
2O defect also contributes to
N
eff. This defect is more copiously produced during
24
GeV/
c
proton irradiation than during 1
MeV neutron irradiation on account of the higher vacancy introduction rate, hence the radiation hardness of materials is more sensitive to impurity concentrations in the case of protons than neutrons. We conclude that naı̈ve normalisation of
N
eff data using hardness factors of radiation sources can be misleading, because point defect introduction rates do not necessarily scale with non-ionising energy loss.
Radiation hardness is a critical design concern for present and future silicon detectors in high energy physics. Tracking systems at the CERN Large Hadron Collider (LHC) are expected to operate for ...ten years and to receive fast hadron fluences equivalent to 10/sup 15/cm/sup -2/ 1-MeV neutrons. Recently, low temperature operating conditions have been suggested as a means of suppressing the negative effects of radiation damage on detector charge collection properties. To investigate this effect, simulations have been carried out using the ISE-TCAD DESSIS device simulator. The so-called "three-level model" has been used. A comprehensive analysis of the influence of the V/sub 2/, C/sub i/O/sub i/ and V/sub 2/O capture cross sections on the effective doping concentration (N/sub eff/) as a function of temperature and fluence has been carried out. The capture cross sections have been varied in the range 10/sup -18/-10/sup -12/ cm/sup 2/. The simulated results are compared with charge collection spectra obtained with 1064-nm laser pulses on devices irradiated with 23-GeV protons as a function of detector bias voltage. To validate the model, a wide range of temperature and fluence has been studied using a one-dimensional (1-D) simplified structure. Thousands of simulation results have been cross checked with the experimental data. The data between 190 K (the lower limit for simulations due to computational difficulties) and 290 K are well reproduced for all of the fluences considered. We conclude that the three-level model can be successfully used to predict irradiated detector behavior down to a temperature of at least 190 K.
Radiation hardness is a critical design constraint for current and future generation silicon detectors, which are foreseen to undergo radiation fluences higher than 1×10
14
cm
−2 1-MeV neutron ...equivalent. Recently, low-temperature operating conditions have been suggested as an effective means to recover the negative effects of radiation damage on silicon detector collection properties. In order to investigate such an effect, simulations have been carried out using the ISE-TCAD DESSIS device simulator. The simulated results are compared with charge collection spectra obtained with 1064
nm laser pulses on devices irradiated with 23
GeV protons as a function of detector bias voltage. Thousands of simulation results have been cross-checked with the experimental data. The results obtained so far indicate that the “three-level model” can be successfully extended to predict irradiated detector behavior at least down to a temperature of 190
K.
Defect evolution in irradiated silicon detector material MacEvoy, B.C; Hall, G; Gill, K
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/1996, Letnik:
374, Številka:
1
Journal Article
Recenzirano
A numerical model based on experimental data has been used to investigate the evolution of atomic defects in high resistivity detector material during neutron and gamma irradiation to levels expected ...at the CERN LHC. The complexes V
2O and V
3O have been identified as candidates for deep-level acceptor states which give rise to experimentally observed changes in the effective doping concentration. The phosphorus dopant is removed by production of VP centres but at a rate lower than previously hypothesised and not fully, even after heavy irradiation. The importance of initial oxygen and carbon impurity concentrations is demonstrated in determining the radiation tolerance of the detectors. A hypothesis for the long term annealing behaviour via the thermal annealing of a trivacancy (V
3) state during neutron and heavy particle irradiation is modelled and shown to be a possible explanation of experimental observations.
Silicon detectors in particle physics experiments at the CERN Large Hadron Collider will be exposed to unprecedented levels of radiation. The principal obstacle to long-term operation in this ...environment is changes in detector effective doping concentration (Neff). We present a model of defect evolution during gamma and hadron irradiation which has been combined with Shockley–Read–Hall (SRH) statistics to predict Neff and dark current in irradiated devices. These predictions are compared with experimental results from detectors with various oxygen and carbon concentrations. In the case of gamma irradiation, the electrical characteristics are described satisfactorily by the production of divacancy–oxygen (V2O) defects. In the case of hadron irradiation, however, the experimental data cannot be explained in the conventional SRH picture. We propose a model whereby states in the terminal defect clusters exchange charge directly. This mechanism leads to a marked increase in carrier generation rate and an enhancement in the acceptor-like contribution to Neff. We conclude that only limited improvements in radiation hardness to hadrons can be achieved by altering detector impurity levels, since the changes in Neff are dominated by intrinsic defects within the terminal clusters.
The effect of particle irradiation on high-resistivity silicon detectors has been extensively studied with the goal of engineering devices able to survive the very challenging radiation environment ...at the CERN Large Hadron Collider (LHC). The main aspect under investigation has been the changes observed in detector effective doping concentration (N/sub eff/). We have previously proposed a mechanism to explain the evolution of N/sub eff/, whereby charge is exchanged directly between closely-spaced defect centres in the dense terminal clusters formed by hadron irradiation. This model has been implemented in both a commercial finite-element device simulator (ISE-TCAD) and a purpose-built simulation of interdefect charge exchange. To control the risk of breakdown due to the high leakage currents foreseen during ten years of LHC operation, silicon detectors will be operated below room temperature (around -10/spl deg/C). This, and more general current interest in the field of cryogenic operation, has led us to investigate the behavior of our model over a wide range of temperatures. We present charge collection spectra from 1064 nm laser pulses as a function of detector bias between temperatures of 115 K and 290 K, using devices irradiated with 23 GeV protons in the range 10/sup 13/-4/spl times/10/sup 14/ protons/spl middot/cm/sup -2/. These data allow a deeper investigation of the influence of defect capture cross sections on N/sub eff/. The model prediction for the reversion to n-type of heavily-irradiated detectors at low temperature is investigated and deviations from the model are explored.
High-energy physics experiments, such as the compact muon solenoid (CMS) at the large hadron collider (LHC), have large-scale data processing computing requirements. The grid has been chosen as the ...solution. One important challenge when using the grid for large-scale data processing is the ability to monitor the large numbers of jobs that are being executed simultaneously at multiple remote sites. The relational grid monitoring architecture (R-GMA) is a monitoring and information management service for distributed resources based on the GMA of the Global Grid Forum. We report on the first measurements of R-GMA as part of a monitoring architecture to be used for batch submission of multiple Monte Carlo simulation jobs running on a CMS-specific LHC computing grid test bed. Monitoring information was transferred in real time from remote execution nodes back to the submitting host and stored in a database. In scalability tests, the job submission rates supported by successive releases of R-GMA improved significantly, approaching that expected in full-scale production.
Silicon particle detectors in the next generation of experiments at the CERN Large Hadron Collider will be exposed to a very challenging radiation environment. The principal obstacle to long-term ...operation arises from changes in detector doping concentration (N/sub eff/), which lead to an increase in the bias required to deplete the detector and hence achieve efficient charge collection. We have previously presented a model of interdefect charge exchange between closely spaced centers in the dense terminal clusters formed by hadron irradiation. This manifestly non-Shockley-Read-Hall (SRH) mechanism leads to a marked increase in carrier generation rate and negative space charge over the SRH prediction. There is currently much interest in the subject of cryogenic detector operation as a means of improving radiation hardness. Our motivation, however, is primarily to investigate our model further by testing its predictions over a range of temperatures. We present measurements of spectra from /sup 241/Am alpha particles and 1064-nm laser pulses as a function of bias between 120 and 290 K. Values of N/sub eff/ and substrate type are extracted from the spectra and compared with the model. The model is implemented in both a commercial finite-element device simulator (ISE-TCAD) and a purpose-built simulation of interdefect charge exchange. Deviations from the model are explored and comments made as to possible future directions for investigation of this difficult problem.
In this paper we discuss an enhanced approach to the analysis of radiation-damaged silicon devices, with reference to numerical modelling implemented in a general-purpose device simulator. In ...particular, the emission and capture mechanism of deep levels are accounted for by means of Shockley–Read–Hall theory and shallow-level sensitivity to radiation is considered by means of a donor removal model. The effects produced by regions containing very high defect concentrations (referred to as “clusters”) are considered by calculating the direct charge exchange between two deep levels. The resulting analysis technique has been validated and calibrated by means of comparison with experimental measurements carried out on irradiated samples. The model is shown to provide comprehensive and accurate results for several radiation damage phenomena.
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