Characterization of the Hamamatsu VUV4 MPPCs for nEXO

Abstract

In this paper we report on the characterization of the Hamamatsu VUV4 (S/N: S13370-6152) Vacuum Ultra-Violet (VUV) sensitive Silicon Photo-Multipliers (SiPMs) as part of the development of a solution for the detection of liquid xenon scintillation light for the nEXO experiment. Various SiPM features, such as: dark noise, gain, correlated avalanches, direct crosstalk and Photon Detection Efficiency (PDE) were measured in a dedicated setup at TRIUMF. SiPMs were characterized in the range $163\text{K}\le \text{T}\le 233\text{K}$. At an over voltage of $3.1\pm 0.2$ V and at $\text{T}=163\text{K}$ we report a number of Correlated Avalanches (CAs) per pulse in the $1 \upmu\text{s}$ interval following the trigger pulse of $0.161\pm 0.005$. At the same settings the Dark-Noise (DN) rate is $0.137\pm 0.002{\text{ Hz/mm}}^2$. Both the number of CAs and the DN rate are within nEXO specifications. The PDE of the Hamamatsu VUV4 was measured for two different devices at $\text{T}=233\text{K}$ for a mean wavelength of $189\pm 7\text{ nm}$. At $3.6\pm 0.2$ V and $3.5\pm 0.2$ V of over voltage we report a PDE of $13.4\pm 2.6\%$ and $11\pm 2\%$, corresponding to a saturation PDE of $14.8\pm 2.8\%$ and $12.2\pm 2.3\%$, respectively. Both values are well below the $24\%$ saturation PDE advertised by Hamamatsu. More generally, the second device tested at $3.5\pm 0.2$ V of over voltage is below the nEXO PDE requirement. The first one instead yields a PDE that is marginally close to meeting the nEXO specifications. This suggests that with modest improvements the Hamamatsu VUV4 MPPCs could be considered as an alternative to the FBK-LF SiPMs for the final design of the nEXO detector.