Silicon Photomultipliers as photosensors for liquid xenon detectors are an attractive alternative to photomultiplier tubes: liquid xenon detectors employed in low background experiments or compact Compton cameras can take advantage of the small sensor mass and dimensions, the larger light collection coming from a more packed tiling of the readout plane, and possibly a smaller cost per area. We investigate the operation in liquid xenon of samples developed by Ketek GmbH. To provide sensitivity to the liquid xenon scintillation light wavelength, 178 nm, the inactive entrance layer of the device has been thinned. The operation of such devices at temperatures as low as -100°C has been verified, characterizing dark count rate and after-pulsing as well. In order to not deteriorate the liquid xenon purity, we selected a substrate and a bonding adhesive measuring the outgassing properties of the parts. Finally, we realized a test station to assess the photon detection efficiency at a wavelength of 178 nm. In a cryogenic vacuum-insulated vessel an ~(241)Am α-source and up to four samples are immersed in liquid xenon, allowing an event-by-event comparison of the response of three Silicon Photomultipliers and a 1" Photomultiplier Tube used as reference.
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