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Response of AC-coupled Low Gain Avalanche Detectors to Ionizing and Non-ionizing Radiation Damage

Jiahe Si, Gabriele D'Amen, Mohamed Hijas Mohamed Farook, Gabriele Giacomini, Martin R. Hoeferkamp, Sally Seidel, Alessandro Tricoli

TL;DR

This work assesses radiation hardness of AC-coupled LGADs (AC-LGADs) relative to DC-LGADs under ionizing gamma and non-ionizing proton damage. Using IV and CV measurements, the study quantifies leakage currents, depletion voltages ($V_{gl}$ and $V_{fd}$), and inter-pad surface resistivity, and extracts acceptor-removal constants by fitting $V_{gl}$ versus dose/fluence to exponential forms. Key findings show gamma exposure modestly alters depletion voltages and introduces CV frequency dependence, while proton exposure dramatically increases leakage current and reduces depletion voltages, with AC-LGADs exhibiting somewhat lower damage than DC counterparts. The derived constants, $c_{\gamma}$ for AC-LGADs and $c_{ni}$ for AC-/DC-LGADs, are consistent with prior measurements, providing quantitative inputs for designing LGAD-based sensors for high-radiation environments.

Abstract

Low gain avalanche diodes with DC- and AC-coupled readout were exposed to ionizing and non-ionizing radiation at levels relevant to future experiments in particle, nuclear, and medical physics and to astrophysics. Damage-related change in their acceptor removal constants and in the resistivity of the region between the guard ring and the active area are reported, as is change in the leakage current and depletion voltages of the active volumes.

Response of AC-coupled Low Gain Avalanche Detectors to Ionizing and Non-ionizing Radiation Damage

TL;DR

This work assesses radiation hardness of AC-coupled LGADs (AC-LGADs) relative to DC-LGADs under ionizing gamma and non-ionizing proton damage. Using IV and CV measurements, the study quantifies leakage currents, depletion voltages ( and ), and inter-pad surface resistivity, and extracts acceptor-removal constants by fitting versus dose/fluence to exponential forms. Key findings show gamma exposure modestly alters depletion voltages and introduces CV frequency dependence, while proton exposure dramatically increases leakage current and reduces depletion voltages, with AC-LGADs exhibiting somewhat lower damage than DC counterparts. The derived constants, for AC-LGADs and for AC-/DC-LGADs, are consistent with prior measurements, providing quantitative inputs for designing LGAD-based sensors for high-radiation environments.

Abstract

Low gain avalanche diodes with DC- and AC-coupled readout were exposed to ionizing and non-ionizing radiation at levels relevant to future experiments in particle, nuclear, and medical physics and to astrophysics. Damage-related change in their acceptor removal constants and in the resistivity of the region between the guard ring and the active area are reported, as is change in the leakage current and depletion voltages of the active volumes.

Paper Structure

This paper contains 7 sections, 7 equations, 12 figures, 8 tables.

Table of Contents

  1. Introduction
  2. Gamma Irradiation Studies
  3. Proton Irradiation Studies
  4. Acceptor Removal Constants
  5. Conclusions
  6. Method for Determining Depletion Voltages $V_{\rm gl}$ and $V_{\rm fd}$
  7. Systematic Uncertainties on Leakage Current, Capacitance, and Depletion Voltages

Figures (12)

  • Figure 1: DC-LGAD from wafer 3076 (left); AC-LGAD from wafer 3073 (center); and AC-LGAD from wafer 3080 (right). In each figure, the labels indicate (a) the guard ring, (b) the DC contact pad, and (c) the AC pad or strip, which appears on the AC-LGAD devices only.
  • Figure 2: The leakage current versus bias voltage of AC-LGAD strip sensors for three levels of gamma exposure. (The uncertainty bars on data points below the depletion voltage have been excluded for improved visualization.) The data were collected at temperatures in the range $19.8^\circ$C to $20.0^\circ$C and are all scaled to $20^\circ$C for ease of comparison.
  • Figure 3: Inverse capacitance (C$^{-2}$) versus bias voltage of AC-LGAD strip sensors for two levels of gamma exposure and five applied signal frequencies. The unirradiated case is shown on the left, and the irradiated, on the right. The legends show the temperatures at which the data were collected.
  • Figure 4: Experimental setup for measuring the resistance between the guard ring and readout pads of the LGADs.
  • Figure 5: Resistance from the guard ring to the DC pad, for strip AC-LGADs, as a function of bias voltage for several gamma dose values. The data were collected at approximately $20^\circ$C.
  • ...and 7 more figures