# Simulation-Based Design of a Silicon SPAD with Dead-Space-Aware Avalanche Region for Picosecond-Resolved Detection

## TL;DR

A new silicon SPAD design improves picosecond detection by optimizing electric fields and reducing edge breakdown, enhancing performance for quantum imaging and LiDAR.

## Contribution

A simulation-based SPAD design with guard rings and tailored doping to suppress edge breakdown and improve timing precision.

## Key findings

- The optimized SPAD achieves a peak electric field of 7 × 10⁷ V/m and sub-20 ps response time.
- Guard ring structure reduces edge hotspots and improves breakdown localization and timing consistency.
- Design shows stable gain slope and enhanced performance for high-speed optical communication and quantum imaging.

## Abstract

What are the main findings?

Premature edge breakdown is suppressed by equalizing edge electric fields, enabling higher excess bias while preserving picosecond-level timing and central avalanche confinement.

A compact guard-ring + field-stop layout and bias scheme flattens edge fields (<5% radial margin of the active diameter in our present single-pixel design), with consistent trends across electrostatic, ionization, and transient simulations.

What is the implication of the main finding?

Improves operating margin and robustness of silicon SPAD pixels, supporting scaling toward dense arrays and stable high-bias operation.

Reduces edge hotspots and potential dark-count sources, yielding more uniform breakdown behavior and more consistent timing/jitter in time-resolved detection.

This study presents a simulation-based design of a silicon single-photon avalanche diode (SPAD) optimized for picosecond-resolved photon detection. Utilizing COMSOL Multiphysics, we implement a dead-space-aware impact ionization model to accurately capture history-dependent avalanche behavior. A guard ring structure and tailored doping profiles are introduced to improve electric field confinement and suppress edge breakdown. Simulation results show that the optimized device achieves a peak electric field of 7 × 107 V/m, a stable gain slope of −0.414, and consistent avalanche triggering across bias voltages. Transient analysis further confirms sub-20 ps response time under −6.5 V bias, validated by a full-width at half-maximum (FWHM) of ~17.8 ps. Compared to conventional structures without guard rings, the proposed design exhibits enhanced breakdown localization, reduced gain sensitivity, and improved timing response. These results highlight the potential of the proposed SPAD for integration into next-generation quantum imaging, time-of-flight LiDAR, and high-speed optical communication systems.