In the framework of the CERN-RD50 Collaboration, the adoption of p-type substrates has been proposed as a suitable mean to improve the radiation hardness of silicon detectors up to fluencies of ...1times10 16 n/cm 2 . In this work two numerical simulation models will be presented for p-type and n-type silicon detectors, respectively. A comprehensive analysis of the variation of the effective doping concentration (N eff ), the leakage current density and the charge collection efficiency as a function of the fluence has been performed using the Synopsys T-CAD device simulator. The simulated electrical characteristics of irradiated detectors have been compared with experimental measurements extracted from the literature, showing a very good agreement. The predicted behaviour of p-type silicon detectors after irradiation up to 10 16 n/cm 2 shows better results in terms of charge collection efficiency and full depletion voltage, with respect to n-type material, while comparable behaviour has been observed in terms of leakage current density
Detection of low levels of light is one of the key aspects in medical and space applications. Silicon photomultiplier, a novel type of avalanche photodetector which operates in Geiger mode, shows ...promising results and offer superior design options. The performance characteristics of the SiPM realized in FBK-irst are studied and presented in this paper. The leakage current, dark rate and internal gain are characterized as a function of temperature. The investigation has been carried out in the framework of the DASiPM Collaboration and the INFN/FBK-irst MEMS project.
This paper presents initial results from electrical, spectroscopic and ion beam induced charge (IBIC) characterisation of a novel silicon PIN detector, featuring an on-chip n -channel JFET and ...matched feedback capacitor integrated on its p -side (frontside). This structure reduces electronic noise by minimising stray capacitance and enables highly efficient optical coupling between the detector back-side and scintillator, providing a fill factor of close to 100%. The detector is specifically designed for use in high resolution gamma cameras, where a pixellated scintillator crystal is directly coupled to an array of silicon photodetectors. The on-chip JFET is matched with the photodiode capacitance and forms the input stage of an external charge sensitive preamplifier (CSA). The integrated monolithic feedback capacitor eliminates the need for an external feedback capacitor in the external electronic readout circuit, improving the system performance by eliminating uncontrolled parasitic capacitances. An optimised noise figure of 152 electrons RMS was obtained with a shaping time of 2 mus and a total detector capacitance of 2 pF. The energy resolution obtained at room temperature (2degC) at 27 keV (direct interaction of I-125 gamma rays) was 5.09%, measured at full width at half maximum (FWHM). The effectiveness of the guard ring in minimising the detector leakage current and its influence on the total charge collection volume is clearly demonstrated by the IBIC images.
Thin detectors have been proposed to investigate the possibility to limit the full depletion voltage and the leakage current of heavily irradiated silicon devices. In this work we compare typical ...silicon detectors (p–n junctions over a 300
μm thick substrate) with thinned devices (50–100
μm of thickness). In order to investigate the performances of these structures, simulations have been carried out using the ISE-TCAD DESSIS device simulator. The so called three-level model has been used to investigate the effects of the radiation fluence on charge collection efficiency of thin and thick silicon structures. For each thickness, we simulate the hit of a minimum ionizing particle and then we calculate the current at the diode's electrode. We consider a 7×10
11
cm
−3 n-doped substrate (a high resistivity substrate); all the structures are composed of a 40
μm diode contact and a 15
μm distant guard ring. The simulated collected charge of the 300
μm diode is in agreement with the experimental results; the simulation of thinner structures (50–100
μm) shows a saturation of the number of e–h pairs collected at the diode's electrodes. These results suggest that thin detectors may have a better performance at higher fluences than thick ones. They are maximizing the collected charge at lower depletion voltage.
In time-of-flight measurements, or positron emission tomography experiments where two gamma rays are detected in coincidence, the time resolution of the photodetector is of primary importance. SiPMs ...are very promising devices for these applications, since their intrinsic response time can be less than 1
ns. However the actual timing resolution of SiPM is affected by the area (capacitance) of the device, by the type of used to pre-amplify the signal, by the dark count rate which is revealed as pure noise, and other second order effects like cross-talk and after pulsing. In this work we report the characteristics of different samples of Hamamatsu Photonics (HPK) and Fondazione Bruno Kessler (FBK) SiPM, with pixel size ranging from 40 to 100
μm. In particular, we have investigated their time response when stimulated with O(50)
ps pulsed laser at wavelengths in the range 400–800
nm.
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.
Numerical analysis of thinned silicon detectors Petasecca, M.; Pignatel, G.U.; Moscatelli, F. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2007, Letnik:
572, Številka:
1
Journal Article
Recenzirano
In the framework of the CERN-RD50 and INFN-SMART collaboration, we have investigated the possibility of using thin devices as a solution to improve the reliability of silicon detectors after ...long-term irradiation at the Super-Large Hadron Collider (LHC). In this work, we compare conventional silicon detectors (p-on-n type diodes over a 300
μm thick wafer substrates) with thinned devices (50–100
μm thick). The performance of these structures have been studied by means of a three defect level radiation damage model, implemented in the SYNOPSYS-TCAD device simulator. The effects of the radiation fluence on the effective doping concentration (
N
eff), leakage current and charge collection efficiency (CCE) have been investigated up to irradiation fluencies of 10
16 1
MeV neutron-equivalent/cm
2. The simulations have been compared with experimental measurements carried out on similar test structures irradiated with neutrons and protons at high fluencies.
We report on the design, manufacturing and first characterisation of pad diodes, test structures and microstrip detectors processed with high resistivity magnetic Czochralski (MCz) p- and n-type Si. ...The pre-irradiation study on newly processed microstrip detectors and test structures show a good overall quality of the processed wafers. After irradiation with 24
GeV/
c protons up to 4×10
14
cm
-2 the characterisation of n-on-p and p-on-n MCz Si sensors with the
C–
V method show a decrease of the full depletion voltage and no space charge sign inversion. Microscopic characterisation has been performed to study the role of thermal donors in Czochralski Si. No evidence of thermal donor activation was observed in n-type MCz Si detectors if contact sintering was performed at a temperature lower than 380
°C and the final passivation oxide was omitted.
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.
In the framework of the CERN-RD50 Collaboration, the adoption of p-type substrates has been proposed as a suitable approach to optimize the long-term radiation hardness of silicon detectors. In this ...work, we present a numerical model for the simulation of radiation damage effects in p-type silicon, developed within the general-purpose device simulator DESSIS. The model includes radiation-induced deep-level recombination centers in the semiconductor band-gap and the Shockley–Read–Hall statistics. In particular, two deep-level defects have been introduced: one located at
E
C−0.42
eV, corresponding to a single charge state divacancy and a second one located at
E
C−0.46
eV, corresponding to a single charge state tri-vacancy. For simulation purposes we have considered a simple, two-dimensional test structure, consisting of a single diode of 40
μm width and 300
μm depth, surrounded by a 6
μm wide guard ring. The n+ implant region depth is 1
μm, with donor concentration of
N
D=10
18
cm
−3 implanted on a high-resistivity p-type substrate (
N
A=5×10
12
cm
−3). The results of simulations adopting the proposed radiation damage model for p-type substrate have been compared with experimental measurements carried out on similar test structures irradiated with neutrons at high fluence. A good agreement with the experimental data has been obtained for the depletion voltage and diode leakage current. The simulated current damage constant (α=3.75×10
−17
A
cm
−1) is in satisfactory agreement with values reported in the literature. A preliminary study of charge collection efficiency as a function of the fluence is also reported.
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