6,248 research outputs found
Neutron irradiation effect on SiPMs up to = 5 10 cm
Silicon Photo-Multipliers (SiPM) are becoming the photo-detector of choice
for increasingly more particle detection applications, from fundamental physics
to medical and societal applications. One major consideration for their use at
high-luminosity colliders is the radiation damage induced by hadrons, which
leads to a dramatic increase of the dark count rate. KETEK SiPMs have been
exposed to various fluences of reactor neutrons up to =
510 cm (1 MeV equivalent neutrons). Results from the I-V,
and C-V measurements for temperatures between 30C and 30C
are presented. We propose a new method to quantify the effect of radiation
damage on the SiPM performance. Using the measured dark current the single
pixel occupation probability as a function of temperature and excess voltage is
determined. From the pixel occupation probability the operating conditions for
given requirements can be optimized. The method is qualitatively verified using
current measurements with the SiPM illuminated by blue LED light
Properties of a radiation-induced charge multiplication region in epitaxial silicon diodes
Charge multiplication (CM) in pn epitaxial silicon pad diodes of 75, 100
and 150 \upmum thickness at high voltages after proton irradiation with 1 MeV
neutron equivalent fluences in the order of cm was studied as
an option to overcome the strong trapping of charge carriers in the innermost
tracking region of future Super-LHC detectors. Charge collection efficiency
(CCE) measurements using the Transient Current Technique (TCT) with radiation
of different penetration (670, 830, 1060 nm laser light and -particles
with optional absorbers) were used to locate the CM region close to the
p-implantation. The dependence of CM on material, thickness of the
epitaxial layer, annealing and temperature was studied. The collected charge in
the CM regime was found to be proportional to the deposited charge, uniform
over the diode area and stable over a period of several days. Randomly
occurring micro discharges at high voltages turned out to be the largest
challenge for operation of the diodes in the CM regime. Although at high
voltages an increase of the TCT baseline noise was observed, the
signal-to-noise ratio was found to improve due to CM for laser light. Possible
effects on the charge spectra measured with laser light due to statistical
fluctuations in the CM process were not observed. In contrast, the relative
width of the spectra increased in the case of -particles, probably due
to varying charge deposited in the CM region.Comment: 11 pages, accepted by NIM
Study of X-ray Radiation Damage in Silicon Sensors
The European X-ray Free Electron Laser (XFEL) will deliver 30,000 fully
coherent, high brilliance X-ray pulses per second each with a duration below
100 fs. This will allow the recording of diffraction patterns of single complex
molecules and the study of ultra-fast processes. Silicon pixel sensors will be
used to record the diffraction images. In 3 years of operation the sensors will
be exposed to doses of up to 1 GGy of 12 keV X-rays. At this X-ray energy no
bulk damage in silicon is expected. However fixed oxide charges in the
insulating layer covering the silicon and interface traps at the Si-SiO2
interface will be introduced by the irradiation and build up over time.
We have investigated the microscopic defects in test structures and the
macroscopic electrical properties of segmented detectors as a function of the
X-ray dose. From the test structures we determine the oxide charge density and
the densities of interface traps as a function of dose. We find that both
saturate (and even decrease) for doses between 10 and 100 MGy. For segmented
sensors the defects introduced by the X-rays increase the full depletion
voltage, the surface leakage current and the inter-pixel capacitance. We
observe that an electron accumulation layer forms at the Si-SiO2 interface. Its
width increases with dose and decreases with applied bias voltage. Using TCAD
simulations with the dose dependent parameters obtained from the test
structures, we are able to reproduce the observed results. This allows us to
optimize the sensor design for the XFEL requirements
Optimization of the Radiation Hardness of Silicon Pixel Sensors for High X-ray Doses using TCAD Simulations
The European X-ray Free Electron Laser (XFEL) will deliver 27000 fully
coherent, high brilliance X-ray pulses per second each with a duration below
100 fs. This will allow the recording of diffraction patterns of single
molecules and the study of ultra-fast processes. One of the detector systems
under development for the XFEL is the Adaptive Gain Integrating Pixel Detector
(AGIPD), which consists of a pixel array with readout ASICs bump-bonded to a
silicon sensor with pixels of 200 {\mu}m \times 200 {\mu}m. The particular
requirements for the detector are a high dynamic range (0, 1 up to 10E5 12 keV
photons/XFEL-pulse), a fast read-out and radiation tolerance up to doses of 1
GGy of 12 keV X-rays for 3 years of operation. At this X-ray energy no bulk
damage in silicon is expected. However fixed oxide charges in the SiO2 layer
and interface traps at the Si-SiO2 interface will build up. As function of the
12 keV X-ray dose the microscopic defects in test structures and the macro-
scopic electrical properties of segmented sensors have been investigated. From
the test structures the oxide charge density, the density of interface traps
and their properties as function of dose have been determined. It is found that
both saturate (and even decrease) for doses above a few MGy. For segmented
sensors surface damage introduced by the X-rays increases the full depletion
voltage, the surface leakage current and the inter-pixel capacitance. In
addition an electron accumulation layer forms at the Si-SiO2 interface which
increases with dose and decreases with applied voltage. Using TCAD simulations
with the dose dependent damage parameters obtained from the test struc- tures
the results of the measurements can be reproduced. This allows the optimization
of the sensor design for the XFEL requirements
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