3,467 research outputs found
Preliminary characterisation of 3D and LGAD prototypes. Test set-up ready in the laboratories
While designing of 3D and LGAD AIDAinnova sensors within WP6 has been completed and production is on-going, results from prototype sensors of similar design from previous productions are summarized in this report. These results demonstrate the readiness of the institutes to assess the performance of the incoming devices from WP6 productions
Three-dimensional charge transport mapping by two-photon absorption edge transient-current technique in synthetic single-crystalline diamond
We demonstrate the application of two-photon absorption transient current
technique to wide bandgap semiconductors. We utilize it to probe charge
transport properties of single-crystal Chemical Vapor Deposition (scCVD)
diamond. The charge carriers, inside the scCVD diamond sample, are excited by a
femtosecond laser through simultaneous absorption of two photons. Due to the
nature of two-photon absorption, the generation of charge carriers is confined
in space (3-D) around the focal point of the laser. Such localized charge
injection allows to probe the charge transport properties of the semiconductor
bulk with a fine-grained 3-D resolution. Exploiting spatial confinement of the
generated charge, the electrical field of the diamond bulk was mapped at
different depths and compared to an X-ray diffraction topograph of the sample.
Measurements utilizing this method provide a unique way of exploring spatial
variations of charge transport properties in transparent wide-bandgap
semiconductors.Comment: This article may be downloaded for personal use only. Any other use
requires prior permission of the author and AIP Publishing. The following
article appeared in Applied Physics Letters and may be found at
https://doi.org/10.1063/1.509085
Bias dependence and bistability of radiation defects in silicon
Influence of bias on effective dopant concentration in neutron and pion irradiated diodes has been measured. Detailed studies of annealing of the bias-induced damagehave revealed three components, with introduction rates from 0.005 to 0.008 cm andannealing time constants ranging from 5 to 1000 hours at 20C. Variation of annealing temperatures yielded activation energies around 1 eV for all the three components. Bistable behavior of radiation damage under bias has been observed and its activation and annealingstudied. The bistable damage was associated to the fastest annealing component of bias-induced damage.Using the parameterization obtained, a prediction for ATLAS SCT operation was made.Bias-induced damage is shown to require an additional 80 V to fully deplete detectors at the end of LHC operation
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
Gain and time resolution of 45 m thin Low Gain Avalanche Detectors before and after irradiation up to a fluence of n/cm
Low Gain Avalanche Detectors (LGADs) are silicon sensors with a built-in
charge multiplication layer providing a gain of typically 10 to 50. Due to the
combination of high signal-to-noise ratio and short rise time, thin LGADs
provide good time resolutions.
LGADs with an active thickness of about 45 m were produced at CNM
Barcelona. Their gains and time resolutions were studied in beam tests for two
different multiplication layer implantation doses, as well as before and after
irradiation with neutrons up to n/cm.
The gain showed the expected decrease at a fixed voltage for a lower initial
implantation dose, as well as for a higher fluence due to effective acceptor
removal in the multiplication layer. Time resolutions below 30 ps were obtained
at the highest applied voltages for both implantation doses before irradiation.
Also after an intermediate fluence of n/cm, similar
values were measured since a higher applicable reverse bias voltage could
recover most of the pre-irradiation gain. At n/cm, the
time resolution at the maximum applicable voltage of 620 V during the beam test
was measured to be 57 ps since the voltage stability was not good enough to
compensate for the gain layer loss. The time resolutions were found to follow
approximately a universal function of gain for all implantation doses and
fluences.Comment: 17 page
Radiation Hardness of Thin Low Gain Avalanche Detectors
Low Gain Avalanche Detectors (LGAD) are based on a n++-p+-p-p++ structure
where an appropriate doping of the multiplication layer (p+) leads to high
enough electric fields for impact ionization. Gain factors of few tens in
charge significantly improve the resolution of timing measurements,
particularly for thin detectors, where the timing performance was shown to be
limited by Landau fluctuations. The main obstacle for their operation is the
decrease of gain with irradiation, attributed to effective acceptor removal in
the gain layer. Sets of thin sensors were produced by two different producers
on different substrates, with different gain layer doping profiles and
thicknesses (45, 50 and 80 um). Their performance in terms of gain/collected
charge and leakage current was compared before and after irradiation with
neutrons and pions up to the equivalent fluences of 5e15 cm-2. Transient
Current Technique and charge collection measurements with LHC speed electronics
were employed to characterize the detectors. The thin LGAD sensors were shown
to perform much better than sensors of standard thickness (~300 um) and offer
larger charge collection with respect to detectors without gain layer for
fluences <2e15 cm-2. Larger initial gain prolongs the beneficial performance of
LGADs. Pions were found to be more damaging than neutrons at the same
equivalent fluence, while no significant difference was found between different
producers. At very high fluences and bias voltages the gain appears due to deep
acceptors in the bulk, hence also in thin standard detectors
Linear plasmon dispersion in single-wall carbon nanotubes and the collective excitation spectrum of graphene
We have measured a strictly linear pi-plasmon dispersion along the axis of
individualized single wall carbon nanotubes, which is completely different from
plasmon dispersions of graphite or bundled single wall carbon nanotubes.
Comparative ab initio studies on graphene based systems allow us to reproduce
the different dispersions. This suggests that individualized nanotubes provide
viable experimental access to collective electronic excitations of graphene,
and it validates the use of graphene to understand electronic excitations of
carbon nanotubes. In particular, the calculations reveal that local field
effects (LFE) cause a mixing of electronic transitions, including the 'Dirac
cone', resulting in the observed linear dispersion
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