Investigating ultra-thin 4H-SiC AC-LGADs for superior radiation-hard timing applications

The Low Gain Avalanche Diodes (LGADs) are promising particle detectors for timing resolution better than $50$ ps under a high radiation environment. This study investigates n-in-p LGAD architecture, focusing on ultra-thin sensors of thickness less than $50\mu$m using the WeightField2 program. The capabilities of WeightField2 are demonstrated by comparing its results with irradiation measurements from an FBK LGAD wafer, showing good agreement across unirradiated and neutron-irradiated conditions. This paper presents device simulations in High Luminosity LHC conditions (lifetime integrated fluence $\mathcal{O}({10}^{14}){\mathrm{n}}_{\mathrm{e}\mathrm{q}}\mathrm{c}{\mathrm{m}}^{-2}$, temperature $\approx 243\mathrm{K}$), and taking into account radiation damage, gain reduction due to fluence, and lattice defects. It is shown that a 20 $\mu$m thick sensor achieves the best timing performance. Among Silicon (Si), Diamond ©, and 4H-Silicon Carbide (4H-SiC), we found 4H-SiC to be the most promising: it provides the highest gain value for a fixed thickness and gain implant layer configuration, and best retains high charge collection value and timing capability under increasing fluence up to $50\times {10}^{14}{\mathrm{n}}_{\mathrm{e}\mathrm{q}}\mathrm{c}{\mathrm{m}}^{-2}$. A time resolution less than 25 ps is reported with different gain implant concentrations for a $20\mu$m 4H-SiC sensor. This work presents the potential of SiC-based LGADs in high-radiation collider environments.