Simulation of gain suppression dynamics in low gain avalanche detectors (LGAD): coupling avalanche multiplication with multi-body Coulomb interaction

The phenomenon of gain suppression in low gain avalanche detectors (LGAD) is studied with a custom numerical tool developed for the computation of the electron-hole dynamics and signal formation in planar semiconductor radiation detectors. It adopts a multi-body approach, i.e. the evolution and interaction of the charge cloud is tracked on an individual carrier basis, using a combination of numerical ordinary differential equation solvers and Monte Carlo methods. The Coulomb interaction is treated with particular care as it is critical for the correct simulation of non-linear behaviors of high-density ionization tracks in avalanche structures. By employing a multi-body framework, this work unveils the physical mechanism of gain suppression, demonstrating how local field screening directly drives the reduction in impact ionization rates. The code is validated through comparison with experimental data from an LGAD structure operated under different reverse bias voltages and charge injection levels, showing excellent agreement.