Lorentz shift measurements in heavily irradiated silicon detectors in high magnetic fields

TL;DR

This study measures how high magnetic fields and radiation affect charge drift and Lorentz shift in silicon detectors, revealing changes in behavior post-irradiation that impact sensor performance.

Contribution

It provides the first detailed analysis of Lorentz shift dependence on radiation fluence in silicon sensors under high magnetic fields.

Findings

Lorentz shift for holes increases with radiation fluence.

Lorentz shift for electrons decreases and can change sign after irradiation.

Irradiation alters the electric field structure, affecting charge drift behavior.

Abstract

An external magnetic field exerts a Lorentz force on drifting electric charges inside a silicon strip sensor and thus shifts the cluster position of the collected charge. The shift can be related to the Lorentz angle which is typically a few degrees for holes and a few tens of degrees for electrons in a 4 T magnetic field. The Lorentz angle depends upon magnetic field, electric field inside the sensor and temperature. In this study the sensitivity to radiation for fluences up to 10^16 n/cm^2 has been studied. The Lorentz shift has been measured by inducing ionization with 670 nm red or 1070 nm infrared laser beams injected into the back side of the irradiated silicon sensor operated in magnetic fields up to 8 T. For holes the shift as a function of radiation is increasing, while for electrons it is decreasing and even changes sign. The fact that for irradiated sensors the Lorentz shift for electrons is smaller than for holes, in contrast to the observations in non-irradiated sensors, can be qualitatively explained by the structure of the electric field in irradiated sensors.