The edge transient-current technique (Edge-TCT) and charge-collection measurements with passive test structures made with the LFoundry 150-nm CMOS process on a p-type substrate with an initial ...resistivity of over 3 kΩcm are presented. The measurements were made before and after irradiation with reactor neutrons up to 2⋅1015 neq/cm2. Two sets of devices were investigated: unthinned (700 μm) with the substrate biased through the implant on top and thinned (200 μm) with a processed and metallised backplane.
The depletion depth was estimated with the Edge-TCT and the collected charge was measured with a 90Sr source using an external amplifier having a 25-ns shaping time. The depletion depth for a given bias voltage decreased with the increasing neutron fluence, but it was still larger than 70 μm at 250 V after the highest fluence. After irradiation a much higher collected charge was measured for the thinned detectors with a processed backplane compared to the unthinned devices, although the same or an even larger depletion depth was measured in the unthinned devices. The most probable value of the collected charge of over 5000 electrons was measured with a thinned device also after irradiation to 2⋅1015 neq/cm2. This is sufficient to ensure the successful operation of these detectors at the outer layer of the pixel detector in the ATLAS experiment at the upgraded HL-LHC.
A Transient Current Technique (TCT) utilizing an IR laser with 100 ps pulse width and beam diameter of FWHM = 8 μm was used to evaluate non-irradiated and irradiated p-type silicon micro-strip ...detectors. The beam was parallel with the surface and perpendicular to the strips (Edge-TCT) so that the electron hole pairs were created at known depth in the detector. Induced current pulses were measured in one of the strips. The pulse shapes were analyzed in a new way, which does not require the knowledge of effective trapping times, to determine drift velocity, charge collection and electric field profiles in heavily irradiated silicon detectors. The profiles were studied at different laser beam positions (depth of carrier generation), voltages and fluences up to 5·10 15 neutrons cm -2 . A strong evidence for charge multiplication at high voltages was found with the detector irradiated to the highest fluence.
Studies of inter-pad distance in Low Gain Avalanche Detectors Skomina, P.; Hiti, B.; Cindro, V. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2022, Letnik:
1027
Journal Article
Recenzirano
The effective inter-pad distance of low gain avalanche detector prototypes for ATLAS-HGTD from two producers were investigated. The dependence of the effective inter-pad distance on bias voltage and ...fluence was systematically measured with Transient Current Technique using different laser wavelengths. Bending of the electric field lines at the edges of the electrodes was found to be the reason for the difference between measured and nominal inter-pad distances. The effective inter-pad distances were also simulated and compared to the measurements.
A method is presented which allows to obtain the position-dependent electric field and charge density by fits to velocity profiles from edge-TCT data from silicon strip detectors. The validity and ...the limitations of the method are investigated by simulations of non-irradiated n+p pad sensors and by the analysis of edge-TCT data from non-irradiated n+p strip detectors. The method is then used to determine the position dependent electric field and charge density in n+p strip detectors irradiated by reactor neutrons to fluences between 1 and 10×1015 cm−2 for forward-bias voltages between 25 V and up to 550 V and for reverse-bias voltages between 50 V and 800 V. In all cases the velocity profiles are well described. The electric fields and charge densities determined provide quantitative insights into the effects of radiation damage for silicon sensors by reactor neutrons.
Gain dependence on free carrier concentration in LGADs Kramberger, G.; Hiti, B.; Cindro, V. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2023, Letnik:
1046
Journal Article
Recenzirano
Odprti dostop
Low gain avalanche detectors (LGADs) were investigated with transient current technique utilizing 1064 nm light to determine the effect of ionization density on the measured gain. The ionization ...density was varied with laser intensity and width of the beam spot. A model was derived explaining the decrease of gain due to the polarization of the gain layer, which reduces the electric field. The model was also tested at different ionization densities for LGADs of different gain layer design.
Studies of annealing at temperatures up to 450 °C with Low Gain Avalanche Detectors (LGAD) irradiated with neutrons are described. It was found that the performance of LGADs irradiated with 1.5e15 ...n/cm2 was already improved at 5 min of annealing at 250 °C. Isochronal annealing for 30 min in 50 °C steps between 300 °C and 450 °C showed that the largest beneficial effect of annealing is at around 350 °C. Another set of devices was annealed for 60 min at 350 °C and this annealing significantly increased depletion voltage of the gain layer (Vgl). The effect is equivalent to reducing the effective acceptor removal constant by a factor of ∼ 4. Increase of Vgl is the consequence of increased effective space charge in the gain layer caused by formation of electrically active defects or re-activation of interstitial boron atoms.
A set of Low Gain Avalanche Detectors from Hamamatsu Photonics were irradiated with different neutron fluxes to an integrated fluence of 4⋅1014 cm−2 neutron equivalent. The range of neutron fluxes ...covered was from 1010 cm−2 s−1 to around 4.5⋅1015 cm−2 s−1. The gain layer and bulk depletion voltage as well as charge collection and timing performance were measured after 80 min at 60°C annealing point. The irradiation induced damage was not observed to be dependent on the neutron flux.
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