TCAD and Garfield++ Optimisation of Single-Electrode Silicon Electron Multiplier Sensors

The Silicon Electron Multiplier (SiEM) is a novel silicon sensor concept for minimum-ionising particle (MIP) detection in which internal gain is achieved through a composite electrode structure embedded in the silicon bulk. Unlike conventional gain sensors such as Low-Gain Avalanche Detectors (LGADs), the SiEM produces internal multiplication through electrostatic field shaping rather than through doped gain layers. This architecture is also finely segmented by design, with a pixel pitch of 10 μm, making it a promising candidate for small pitch radiation-hard tracking and timing applications. This work extends the initial conceptual studies by using a three-dimensional Technology Computer-Aided Design (TCAD) and Garfield++ simulation pipeline for simplified single-electrode SiEM geometries. The study evaluates how the multiplication-region geometry affects electrical response, effective charge collection, internal gain, intrinsic timing performance, and the fraction of the pixel area providing a full MIP response. The results show that enlarging the multiplication pillar can improve the effective active area while preserving timing performance comparable to the initial conceptual design.