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

TL;DR

This study investigates charge losses at the Si-SiO2 interface in segmented silicon sensors using time-resolved measurements, revealing how biasing, environment, and irradiation affect charge collection and sensor stability.

Contribution

It introduces a quantitative model for charge losses and accumulation layer widths, incorporating effects of irradiation, biasing history, and environmental conditions.

Findings

Charge losses depend on bias voltage, humidity, and irradiation.

Charge collection efficiency varies with time after biasing, up to days.

Sensor simulations qualitatively explain observed charge loss phenomena.

Abstract

Using multi-channel time-resolved current measurements (multi TCT), the charge collection of p+n silicon strip sensors for electron-hole pairs produced close to the Si-SiO2 interface by a focussed sub-nanosecond 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-SiO2 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+n silicon sensors is discussed.