N-type LGADs for Particle and Photon Detection

19 Nov 2025, 14:40
20m
2F, Activities Center (Academia Sinica)

2F, Activities Center

Academia Sinica

128 Section 2, Academia Road, Nankang, Taipei 115201, Taiwan
ORAL Avalanche-based Sensors 2. Avalanche-based Sensors

Speaker

Giovanni Paternoster (Fondazione Bruno Kessler)

Description

Low-Gain Avalanche Diodes (LGADs) are typically fabricated on p-type substrates, following an n–p$^+$–p junction configuration, where a boron-enriched layer forms the gain region.
This architecture is considered optimal for timing and particle-tracking applications, as the primary charge carriers initiating the avalanche process are electrons, which have a higher drift velocity and ionization coefficient compared to holes. However, for the detection of low-penetrating particles, such as soft X-rays, the conventional p-on-n configuration becomes less efficient. In these cases, most carriers are generated close to the front junction (n-type region) or within the high-field gain layer, resulting in reduced gain, lower signal-to-noise ratio (SNR), and decreased quantum efficiency (QE).
To overcome these limitations and improve the detection efficiency of low-energy photons and particles, LGADs on n-type substrates (N-LGADs) have been recently proposed. This inverted doping configuration, compared to standard LGADs, is expected to deliver higher gain and SNR for low-penetrating radiation, particularly for X-rays below 1 keV.
A new batch of N-LGADs was fabricated at FBK with a twofold objective: (i) to evaluate an optimized junction design for soft X-ray and low-penetrating particle detection, and (ii) to study donor removal effects under high-fluence irradiation. The latter is of increasing relevance for some emerging LGAD technologies, such as Compensated LGADs and Deep-Junction LGADs (DJ-LGADs), both of which rely on an n-type enriched gain layer. In these designs, accurate determination of the donor removal coefficient is a key parameter.
The fabricated N-LGADs employ 55 µm-thick n-type epitaxial substrates, with the front junction formed by boron ion implantation. Several junction depths and doping profiles have been implemented to investigate QE as a function of junction design. The gain layer has been doped with either Phosphorus or Arsenic to assess the donor removal coefficient for both species, and both deep and shallow gain layers were realized.
Electrical characterization (I-V, C-V and gain measurements) will be presented for the different technological splits, along with optical characterization in the 300–900 nm wavelength range. The latter enables determination of QE and gain as a function of the charge generation depth, providing a comprehensive comparison among the various device configurations.

Authors

Giovanni Paternoster (Fondazione Bruno Kessler) Valentina Sola (Università Torino / INFN Torino) Francesco Moscatelli (IOM-CNR and INFN of Perugia) Matteo Centis Vignali (FBK) Maurizio Boscardin (FBK) Dr Ashish Bisht (Fondazione Bruno Kessler) Dr Omar Hammad Ali (Fondazione Bruno Kessler) Roberta Arcidiacono (Università Piemonte Orientale / INFN Torino) Nicolo Cartiglia (INFN Torino) Tommaso Croci (INFN Perugia) Anna Rita Altamura (Università and INFN di Torino) Marco Ferrero (INFN Torino) Alessandro Fondacci (Università and INFN di Perugia) Arianna Morozzi (INFN Perugia) Daniele Passeri (Università and INFN di Perugia) Brendan Regnery (KIT, Karlsruhe) Ling Leander Grimm (KIT, Karlsruhe) Robert Stephen White (INFN di Torino)

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