Nuclear Inst. and Methods in Physics Research, A 982 (2020) 164478 Contents lists available at ScienceDirect Nuclear Inst. and Methods in Physics Research, A journal homepage: www.elsevier.com/locate/nima FBK VUV-sensitive Silicon Photomultipliers for cryogenic temperatures Massimo Capasso a,b,∗ , Fabio Acerbi a,b , Giacomo Borghi a , Andrea Ficorella a , Nicola Furlan a , Alberto Mazzi a,b , Stefano Merzi a,b , Vladimir Mozharov a , Veronica Regazzoni a,b , Nicola Zorzi a,b , Giovanni Paternoster a,b , Alberto Gola a,b a Fondazione Bruno Kessler, Via Sommarive, 18 I-38123, Trento, Italy b Trento Institute for Fundamental Physics and Applications, Via Sommarive, 14 I-38123, Trento, Italy ARTICLE INFO Keywords: Silicon photomultipliers Vacuum ultra-violet Cryogenic SiPMs Liquid Noble-gases scintillators VUV-light detection SiPM performance Scintillation light readout ABSTRACT Fondazione Bruno Kessler (FBK) has been continuously developing and improving silicon photomultiplier tech- nologies, for example with peak efficiency in the blue (near-ultra-violet, NUV), or in the green (red–green–blue, RGB) region of the spectrum. Over the last years there has been a growing interest in silicon photomultipliers (SiPMs) applications at cryogenic temperatures (e.g.: for the readout of the scintillation light from liquefied noble gases in rare-events experiments). One example is the DarkSide-20k experiment, in which LAr scintillation light is detected after wavelength-shifting to match the SiPMs’ spectral response. A dedicated silicon photomultiplier technology has been developed in FBK: the NUV-HD-Cryo. SiPMs made in such technology reach primary dark count rates of about 2 mHz∕mm 2 and an after-pulsing probability of about 12% when biased at 4 V above breakdown in liquid nitrogen (LN). In other experiments, like for example the nEXO experiment, direct detection of vacuum ultra-violet (VUV) light in cryogenic conditions is required. In this case, the sensitivity in VUV has to be combined with the advantages of the ‘‘Cryo’’ technology. In this contribution, the latest results from the cryogenic characterization of FBK VUV-HD technology for cryogenic temperatures will be presented. Among the produced devices, one promising split has been identified with reduced after-pulsing probability at 100 K, less than ‘‘standard’’ VUV-HD device. 1. Introduction Over the past ten years, silicon photomultipliers (SiPMs) have pro- gressively become a valid and reliable alternative to conventional photomultiplier tubes (PMTs), in applications where low-light detec- tion is required. Fondazione Bruno Kessler, FBK (Trento, Italy) has been developing different technologies, with sensitivity optimized for specific spectral regions, ranging from vacuum-ultraviolet to visible and near-infrared [1,2]. One of the most recent developments focused on the realization of NUV-sensitive SiPMs optimized to work at cryo- genic temperatures, for example for the readout of a liquid-argon (LAr) dual-phase time projection chamber (TPC), for the DarkSide- 20k experiment [3]. As described in [4], the three main challenges were: reduction of the primary dark count rate (DCR), reduction of the after-pulsing (AP) probability at cryogenic temperatures and reduced variation of the quenching resistor in such wide temperature range (from room temperature down to ∼80 K). The implementation of new micro-fabrication solutions in order to improve the SiPMs’ performance on all of the above-mentioned parameters, led to the realization of the so-called ‘‘NUV-HD-Cryo’’ technology; SiPMs produced in such tech- nology feature primary DCR of 2 mHz∕mm 2 , with 12% AP probability ∗ Correspondence to: Barnard College, Columbia University, 3009 Broadway, NY 10027-6909, USA. E-mail address: capasso@nevis.columbia.edu (M. Capasso). and a recharge time constant of 270 ns (25 μm cell pitch in liquid nitrogen, LN, 5 V above breakdown [4]). In DarkSide-20k the 128 nm LAr emission is down-shifted to 425 nm through Tetraphenyl butadiene (TPB), in order to match the SiPMs’ spectral sensitivity. Other experiments, however, aim at the direct detection of VUV scintillation light from liquefied noble gases. As an example, in the nEXO experiment [5], 175 nm scintillation light from liquid Xenon (LXe) has to be detected by large SiPM modules. For such applica- tions, VUV-HD technology has been developed and improved at FBK. Lately, the optimization for VUV light detection and the optimization for cryogenic temperature operation have been combined in the new ‘‘VUV-HD-Cryo’’ technology. In the following, the first results of electrical and functional cryo- genic characterization of the latest VUV-HD production from FBK will be presented. 2. Tested technologies and experimental setup Table 1 outlines the main parameters of the tested SiPMs. All the devices feature a 3 × 3 mm 2 active area, with a 35 μm cell pitch. The https://doi.org/10.1016/j.nima.2020.164478 Received 30 January 2020; Received in revised form 21 June 2020; Accepted 28 July 2020 Available online 3 August 2020 0168-9002/© 2020 Published by Elsevier B.V.