Study of impact ionization coefficients in silicon with Low Gain Avalanche Diodes

TL;DR

This study evaluates existing impact ionization models in silicon LGADs against experimental gain measurements, deriving new optimized parameters that better fit the data across various conditions and device types.

Contribution

The paper introduces new parameterizations for impact ionization coefficients in silicon LGADs, improving model accuracy over existing descriptions based on extensive experimental data.

Findings

New impact ionization parameters accurately fit experimental data

Existing models show discrepancies with measured gain data

Optimized models improve TCAD simulation agreement

Abstract

Impact ionization in silicon devices has been extensively studied and several models for a quantitative description of the impact ionization coefficients have been proposed. We evaluate those models against gain measurements on Low Gain Avalanche diodes (LGADs) and derive new parameterizations for the impact ionization coefficients optimized to describe a large set of experimental data. We present pulsed IR-laser based gain measurements on 5 different types of $50\mu m$-thick LGADs from two different producers (CNM and HPK) performed in a temperature range from $-15^oC$ to $40^oC$. Detailed TCAD device models are conceived based on SIMS doping profiles measurements and tuning of the device models to measured C-V characteristics. Electric field profiles are extracted from the TCAD simulations and used as input to an optimization procedure (least squares fit) of the impact ionization model parameters to the experimental data. It is demonstrated that the new parameterizations give a good agreement between all measured data and TCAD simulations which is not achieved with the existing models. Finally, we provide an error analysis and compare the obtained values for the electron and hole impact ionization coefficients against existing models.