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Low Gain Avalanche Diodes (LGADs) represent the state-of-the-art in timing measurements and will instrument future timing detectors at the High Luminosity Large Hadron Collider (HL-LHC) experiments. While conceived as a sensor for charged particles, the intrinsic gain of LGADs makes it possible to detect low energy X-rays with good energy resolution and excellent timing (tens of picoseconds). Using the Stanford Synchrotron Radiation Lightsource (SSRL) at SLAC, several LGADs designs were characterized with energies from 5 to 35 keV. The SSRL provides 10 ps pulsed X-ray bunches separated by 2.1 ns intervals, and with an energy dispersion (Δ E/E) of 1 × 10-4. LGADs fabricated by Hamamatsu Photonics (HPK) and Brookhaven National Laboratory (BNL) with different thicknesses ranging from 20 µm to 50 µm and different gain layer designs were read out a two stage fast amplification circuit and digitized with a high bandwidth, high sampling rate oscilloscope. PIN devices from HPK were characterized as well. A systematic and detailed characterization of the devices' energy linearity, resolution and timing resolution as a function of X-ray energy was performed for different biasing voltages at room temperature. [ABSTRACT FROM AUTHOR]

Low-Gain Avalanche Detectors (LGADs) are a type of thin silicon detector with a highly doped gain layer that provides moderate internal signal amplification. One recent challenge in the use of LGADs, studied by several research groups, is the gain suppression mechanism for large localized charge deposits. Using the CENPA Tandem accelerator at the University of Washington, the response of the LGADs to MeV-range energy deposits from a proton beam was studied. Two LGAD prototypes and a PIN diode were characterized, and the gain of the devices was determined as a function of bias voltage, incidence beam angle and proton energy. This study was conducted in the scope of the PIONEER experiment, an experiment proposed at the Paul Scherrer Institute to perform high-precision measurements of rare pion decays. A range of deposited charge from Minimum Ionizing Particle (MIP, few 10 s of KeV) from positrons to several MeV from the stopping pions/muons is expected in PIONEER; the detection and separation of close-by hits in such a wide dynamic range will be a main challenge of the experiment. To achieve this goal, the gain suppression mechanism has to be understood fully. [ABSTRACT FROM AUTHOR]

In this paper we report results from a neutron irradiation campaign of Ultra-Fast Silicon Detectors (UFSD) with fluences of 1e14, 3e14, 6e14, 1e15, 3e15 and 6e15 neq/cm2. The UFSD used in this study are circular 50 μ m thick Low-Gain Avalanche Detectors (LGAD), with a 1.0 mm diameter active area. Hamamatsu Photonics (HPK), Japan, produced the UFSD with pre-irradiation internal gain in the range 5–70 depending on the bias voltage. The sensors were tested pre-irradiation and post-irradiation with minimum ionizing particles (MIPs) from a 90Sr β -source. The leakage current, internal gain and the timing resolution were measured as a function of bias voltage at −20 °C and −30 °C. The timing resolution of each device under test was extracted from the time difference with a second calibrated UFSD in coincidence, using the constant fraction discriminator (CFD) method for both. The dependence of the gain upon the irradiation fluence is consistent with the acceptor removal mechanism; at −20 °C the highest gain decreases from 70 before radiation to 2 after a fluence of 6e15 n/cm2. Consequently, the timing resolution was found to deteriorate from 20 ps to 50 ps. The results indicate that the most accurate time resolution is obtained varying with fluence the CFD value used to determine the time of arrival, from 0.1 for pre-irradiated sensors to 0.6 at the highest fluence. Key changes to the pulse shape induced by irradiation, i.e. (i) the contribution of charge multiplication not limited to the gain layer zone, (ii) the shortening of the rise time and (iii) the reduced pulse height, were compared with the WF2 simulation program and were found to be in agreement. [ABSTRACT FROM AUTHOR]

Abstract We report results from the testing of 35 μ m thick Ultra-Fast Silicon Detectors (UFSD) produced by Hamamatsu Photonics (HPK), Japan and the comparison of these new results to data reported in a previous paper on 50 μ m thick UFSD produced by HPK. The 35 μ m thick sensors were irradiated with neutrons to fluences of 1 ⋅ 10 14 , 1 ⋅ 10 15 , 3 ⋅ 10 15 , 6 ⋅ 10 15 neq/cm 2. The sensors were tested pre-irradiation and post-irradiation with minimum ionizing particles (MIPs) from a 90Sr β -source. The leakage current, capacitance, internal gain and the timing resolution were measured as a function of bias voltage at −20 °C and −27 °C. The timing resolution was extracted from the time difference with a second calibrated UFSD in coincidence, using the constant fraction discrimination method for both devices. Within the fluence range measured, 35 μ m thick UFSD present advantages in timing accuracy, bias voltage and power consumption. [ABSTRACT FROM AUTHOR]

Low Gain Avalanche Detectors (LGADs) are based on a n + + -p + -p-p + + structure where appropriate doping of multiplication layer (p + ) leads to high enough electric fields for impact ionization. Operation of these detectors in harsh radiation environments leads to decrease of gain attributed to the effective acceptor removal in the multiplication layer. In order to cope with that devices were produced where boron was replaced by gallium. The initial radiation hardness studies show a smaller degradation of gain with neutron fluence indicating that gallium is more difficult to displace/deactivate from the lattice site than boron. [ABSTRACT FROM AUTHOR]

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 μ m). 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 5 ⋅ 1 0 15 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 μ m) and offer larger charge collection with respect to detectors without gain layer for fluences < 2 ⋅ 1 0 15 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. [ABSTRACT FROM AUTHOR]