Characterization of Silicon Photomultipliers for nEXO
Silicon Photomultipliers (SiPMs) are attractive candidates for light detectors for next generation liquid xenon double-beta decay experiments, like nEXO. One of the main requirements that the SiPMs must satisfy in order to be suitable for nEXO is high photon detection efficiency (PDE) at 175 nm, either directly or using a wavelength shifter. In addition, the devices should demonstrate sufficiently low levels of dark noise and correlated avalanche rates at liquid xenon temperature. We currently collaborate with several manufacturers for the development of SiPMs with high photon detection efficiency at 175nm. In parallel, we are also investigating new wavelength shifting materials produced by Luminotech (Moscow, Russia) that are coated on top of SiPMs and promise high performance, ease of handling, and compatibility with operation in liquid xenon. Devices produced by FBK, Hamamatsu, and other vendors have been characterized in details, measuring key SiPM parameters at cryogenic temperatures (-100C) in vacuum including absolute PDE at 175 nm, rates of dark noise, after-pulses, and cross-talk. A new test setup has recently been commissioned for measuring SiPMs performance in liquid xenon. Additionally, the nEXO collaboration is performing sensitive assessment of radioactivity content of the SiPMs to ensure that their pass our stringent radio-purity requirements. In this talk, we will describe the test setups, the measurement approaches, and present recent results obtained with the latest generations of SiPMs produced by FBK, Hamamatsu, and other vendors, including Hamamatsu MPPCs coated with wavelength shifters.