Radiation effects in Low Gain Avalanche Detectors after hadron irradiations

Abstract

Novel silicon detectors with charge gain were designed (Low Gain Avalanche Detectors - LGAD) to be used in particle physics experiments, medical and timing applications. They are based on a n++-p+-p structure where appropriate doping of multiplication layer (p^+) is needed to achieve high fields and impact ionization. Several wafers were processed with different junction parameters resulting in gains of up to 16 at high voltages. In order to study radiation hardness of LGAD, which is one of key requirements for future high energy experiments, several sets of diodes were irradiated with reactor neutrons, 192 MeV pions and 800 MeV protons to the equivalent fluences of up to Φeq=1016 cm−2. Transient Current Technique and charge collection measurements with LHC speed electronics were employed to characterize the detectors. It was found that the gain decreases with irradiation, which was attributed to effective acceptor removal in the multiplication layer. Other important aspects of operation of irradiated detectors such as leakage current and noise in the presence of charge multiplication were also investigated.

4D tracking with ultra-fast silicon detectors

“…Figure 26 Collected charge for 300 µm thick n-on-p sensors as a function of fluence. Figure taken with permission from [37] Acceptor creation by deep traps and initial acceptor (Boron) removal [38] in silicon detectors can be parameterized according to the following expression:…”

“…where Figure 27 have been taken from [38] and from presentations at TREDI 2017 8 . WF2 uses the parameterizations shown on the plot to account for this effect.…”

“…The root cause of initial acceptor removal is still under investigation [38], however simulations and experimental evidence seem to exclude known radiation effects like "Space Charge Inversion" or "Double-Junction" as the cause for the apparent reduction in the doping concentration. Interestingly, physical removal of boron atoms can be excluded from kinetic considerations and direct SIMS measurements.…”

Tracking in 4 dimensions

“…This effect has not been understood yet, but there are two possible explanations: (i) an inactivation of acceptors due to radiation defects [13], and (ii) a dynamic reduction of the gain layer doping due to charge trapping.…”

Study of gain homogeneity and radiation effects of Low Gain Avalanche Pad Detectors

“…The advantage of the introduced gain is an increased signal to noise ratio which is expected to improve timing properties in LGAD devices compared to regular planar sensors. In addition leads an increased signal to an improved signal-to-noise ratio (SNR) in radiation damaged highly segmented sensors where the noise is not dominated by the radiation induced leakage current [6]. Timing properties and performance after irradiation are the reason for increased interest in this technology which led to several activities within the CERN RD50 collaboration [7].…”