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Göttingen 2025 – scientific programme

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T: Fachverband Teilchenphysik

T 6: Silicon Detectors II (Belle II, Tristan)

T 6.2: Talk

Monday, March 31, 2025, 17:00–17:15, VG 1.101

Investigation of high backside currents in DePFET pixel sensors for the Belle II experiment using dedicated test structuresFlorian Bernlochner, Jochen Dingfelder, •Georgios Giakoustidis, and Botho Paschen — University of Bonn, Germany

For the Belle II experiment at KEK (Tsukuba, Japan) the KEKB accelerator was upgraded to deliver e+e collisions at a center-of-mass energy of ECM = 10.58 GeV and it has reached a record-breaking instantaneous luminosity of 4.7·1034 cm−2s−1. During the so-called Long Shutdown 1 (LS1) the innermost part of the Belle II detector, the initially descoped PiXel Detector (PXD1) with 20 modules, based on Depleted P-channel Field Effect Transistor (DePFET) technology, was replaced by a fully-populated, two-layer PXD with 40 modules. As the detector closest to the experiment’s interaction region, the PXD is most exposed to radiation from the accelerator. Throughout the operation of the PXD1 a steady increase of backside current with irradiation was observed in several modules. Doping-profile measurements and electric field simulations show that this is a consequence of (partially) shorted guard rings at the backside leading to high electric fields and avalanche current multiplication. Irradiation results of dedicated test structures to further investigate the mechanism will be presented.

Keywords: DEPFET; PXD; Belle II; SuperKEKB

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