Charge losses in segmented silicon sensors at the Si–SiO2 interface

Abstract

a b s t r a c tUsing multi-channel time-resolved current measurements (multi-TCT), the charge collection of p þ n silicon strip sensors for electron-hole pairs produced close to the Si-SiO 2 interface by a focussed subnanosecond laser with a wavelength of 660 nm has been studied. Sensors before and after irradiation with 1 MGy of X-rays have been investigated. The charge signals induced in the readout strips and the rear electrode as a function of the position of the light spot are described by a model which allows a quantitative determination of the charge losses and of the widths of the electron-accumulation and hole-inversion layers close to the Si-SiO 2 interface. Depending on the applied bias voltage, biasing history and environmental conditions, like humidity, incomplete electron or hole collection and different widths of the accumulation layers are observed. In addition, the results depend on the time after biasing the sensor, with time constants which can be as long as days. The observations are qualitatively explained with the help of detailed sensor simulations. Finally, their relevance for the detection of X-ray photons and charged particles, and for the stable operation of segmented p þ n silicon sensors is discussed.

Measurement and modelling of anomalous polarity pulses in a multi-electrode diamond detector

“…Thus, the study of the bulk recombination processes in diamond enables us to adopt and validate a general model based on a purely electrostatic approach and relying on the Shockley-Ramo-Gunn (SRGT) theorem [16,17]. The generality of the latter will allow a straightforward application to multi-electrode devices in any detector material, and a further corroboration of results in [1,8,9].…”

“…Pulse height defects and charge losses [1], charge collection efficiency (CCE) losses and spectra distortion [4][5][6], ambipolar transient current signals [7] and anomalous polarity pulses [8,9] have been reported so far. Specifically, we adopt the "anomalous polarity pulse" term to refer to an induced charge pulse having the opposite polarity to what would be detected in a standard device with two large parallel electrodes [9].…”

“…A few studies [1,8,9] proposed the Shockley-Ramo theory [10,11] and its extensions as the basis of the interpre-28005-p1 tation of such phenomena, and identified the occurring of anomalous polarity pulses as a key fingerprint of charge sharing in strip detector geometry [8,9].…”

“…Moreover, charge losses and anomalous polarity pulses were attributed to carriers recombination [14], to a modification of the electric field and the charge collection geometries by the presence of charges trapped at the surface [1,8,9] or by radiation damage effects [1].…”

The CMS Silicon Pixel detector for HL-LHC

“…Figure 5 shows the collected charge, measured using an infrared laser setup, for irradiated pad diodes with an active thickness of 200 µm as a function of fluence for a bias voltage of 900 V. At the highest 1 MeV neutron equivalent fluence considered in this study (1.3 × 10 16 n eq /cm 2 ), 5000 electrons are collected for this rather high bias voltage. Figure 6 shows the collected charge as a func- Figure 5: Collected charge for pad diodes at 900 V as a function of fluence for irradiation with 23 GeV protons and neutrons, after 10 minutes annealing at 60°C [8]. Both n + -in-p (P) and p + -in-n (N) diodes were measured.…”