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

TL;DR

This study uses WeightField2 to predict the timing performance and radiation tolerance of ultra-thin AC-LGADs, comparing simulations with FBK FBK_W6 data to validate the approach. It finds that 20 μm thick 4H-SiC (4H-SiC) bulk AC-LGADs provide the best timing stability under HL-LHC–like irradiation, achieving sub-25 ps resolution across a wide fluence range when gain-layer doping is optimized. The work demonstrates that SiC offers superior radiation hardness and faster charge transport than Si, maintaining higher gain and charge collection at high fluences, while temperature and bias play critical roles in preserving timing performance. Together, these results position ultra-thin SiC-based AC-LGADs as strong candidates for 4D tracking in extreme collider environments, though experimental verification of irradiation evolution in 4H-SiC gain layers remains an open area for future work.

Abstract

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 $50\ μ$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_{eq}~cm^{-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 $μ$m thick sensor achieves the best timing performance. Among Silicon (Si), Diamond (C), 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 $50\times10^{14}\ \mathrm{n_{eq}~cm^{-2}}$. A time resolution less than 25 ps is reported with different gain implant concentrations for a $20 μ$m 4H-SiC sensor. This work presents the potential of SiC-based LGADs in high-radiation collider environments.

Figures (12)

• Figure 1: A typical AC-LGAD architecture
• Figure 2: Comparison of WF2 simulated (a) gain and (b) rise time with experimental data from the FBK W6 LGAD sensor FBK_W6, for both unirradiated (293 K) and neutron-irradiated (253 K) conditions at various fluence levels. In each plot, the markers labelled as W6 refer to FBK wafer 6 data while markers labelled as WF2 are simulation predictions from WeightField2.
• Figure 3: Simulation results for detectors of $20~\upmu$m thickness and operated at $V_{bias}\ =\ 150\ V$ and temperature of 243 K.
• Figure 4: Simulation predictions of time resolution variation as a function of thickness for different fixed-gain SiC bulk AC-LGAD at the constant $V_{bias}$ of $300\ V$
• Figure 5: Figures show WF2 predictions of change in gain value of Si and SiC devices with increasing G.I. dopant concentration. Top: The variation of gain with increasing doping concentration of the gain layer in 20 $\upmu$m, 50 $\upmu$m and 70 $\upmu$m SiC and Si bulk AC-LGAD with quadratic fits. Bottom: First derivative of the quadratic fits of the corresponding curves.