Breakdown Voltage of VUV SiPMs as a Function of Temperature*

The tonne-scale nEXO experiment will search for 0νββ decay using a liquid xenon time projection chamber enriched to 90% ¹³⁶Xe. The chamber will be instrumented with vacuum ultraviolet (VUV) silicon photomultipliers (SiPMs) to sense the scintillation light. We present our study of the breakdown voltage of an FBK VUVHD3 SiPM as a linear function of temperature, in the context of the nEXO collaboration. We measure the breakdown voltage of the SiPM in different environmental conditions, including vacuum, gaseous xenon, gaseous nitrogen, and liquid xenon. We describe our experimental methodology, analysis of the data, calculation of systematic errors, and the interpretation of the results. In the course of this analysis we also report on the absolute gain of the SiPM and correlated avalanche probability.