Simulation of charge transport at the surface of planar silicon sensors

TL;DR

This paper investigates the electric field and charge transport mechanisms at the surface of planar silicon sensors, using simulations and measurements to improve understanding of surface breakdown phenomena in radiation-hard silicon detectors.

Contribution

It develops and validates new simulation methods for the electric field and charge collection at the sensor surface, enhancing the accuracy of modeling surface breakdown in silicon sensors.

Findings

Simulation results agree with measurements of electrical behavior.

Laser scans confirm the accuracy of electric field simulations.

Charge collection efficiency is improved by understanding surface effects.

Abstract

Radiation-hard silicon sensors used in high-energy physics require a high electric field and are susceptible to surface breakdown. This study aims to improve the understanding of the underlying mechanisms by developing new methods to probe the electric field at surface near the sensor's edge. For planar sensors, avalanche breakdown primarily occurs at the Si-SiO2 interface, where localized electric field peaks can form between the guard ring and the edge. Accurate simulations are challenging and it is essential to validate simulation parameters by comparing the simulation results to measurements. In this work, the electrical behavior of the edge region of planar silicon diodes was simulated using Synopsis TCAD. Transient Current Technique (TCT) simulations were performed in both TCAD and Allpix Squared, and compared to measurements. Additionally, laser scans over the edge region were performed in Allpix Squared to evaluate the simulated surface electric field and charge collection efficiency.