Characterization of iLGADs using soft X-rays

Abstract

Experiments at synchrotron radiation sources and X-ray Free-Electron Lasers in the soft X-ray energy range (250 eV–2 keV) stand to benefit from the adaptation of the hybrid silicon detector technology for low energy photons. Inverse Low Gain Avalanche Diode (iLGAD) sensors provide an internal gain, enhancing the signal-to-noise ratio and allowing single photon detection below 1 keV using hybrid detectors. In addition, an optimization of the entrance window of these sensors enhances their quantum efficiency (QE). In this work, the QE and the gain of a batch of different iLGAD diodes with optimized entrance windows were characterized using soft X-rays at the Surface/Interface:Microscopy beamline of the Swiss Light Source synchrotron. Above 250 eV, the QE is larger than 55% for all sensor variations, while the charge collection efficiency is close to 100%. The average gain depends on the gain layer design of the iLGADs and increases with photon energy. A fitting procedure is introduced to extract the multiplication factor as a function of the absorption depth of X-ray photons inside the sensors. In particular, the multiplication factors for electron- and hole-triggered avalanches are estimated, corresponding to photon absorption beyond or before the gain layer, respectively.

Resolving soft X-ray photons with a high-rate hybrid pixel detector

“…The first iLGAD R&D batch devised by the Paul Scherrer Institute (PSI) in collaboration with Fondazione Bruno Kessler (FBK, Trento, Italy) contains iLGADs with optimized thin entrance window and different gain layer designs labelled "standard," "shallow," and "ultra-shallow." For the "standard" gain layer design 1 investigated in this work, the hole multiplication factor is about 25% of the electron multiplication factor, as has been shown with simulations [19] and also reported in [29] with measurements. As a consequence of this design, hole multiplication is the dominant effect for photons with energies below about 500 eV.…”

“…The sensor was bonded to a JUNGFRAU 1.1 readout chip (Figure 2). The quantum efficiency of the investigated iLGAD sensor and its gain layer design have been measured and reported by Liguori et al [29].…”

“…For photons absorbed within the gain layer, both electrons and holes initiate multiplication. The multiplication factors for electrons and holes differ depending on the gain layer design [29]. The first iLGAD R&D batch devised by the Paul Scherrer Institute (PSI) in collaboration with Fondazione Bruno Kessler (FBK, Trento, Italy) contains iLGADs with optimized thin entrance window and different gain layer designs labelled "standard," "shallow," and "ultra-shallow."…”

“…For the standard gain layer design and normal photon incidence angle, electron multiplication dominates at energies > 500 eV. At lower photon energies, hole multiplication becomes important and M reduces by about a factor four [29]. For 200 eV photons at −22 °C, the SNR becomes 1.25 with clustering and 2.5 without.…”

Quantum Efficiency Measurement and Modeling of Silicon Sensors Optimized for Soft X-ray Detection

“…In collaboration with FBK, we also produced an R&D sensor batch based on the inverse LGAD (iLGAD) technology [23] to improve the SNR. These iLGAD sensors also benefit from the optimization of the EW presented in this work, which is essential to obtain high QE for SXRs, as shown in detail in [24].…”