  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 $163 \text{ } \text{K} \leq \text{T}\leq 233
\text{ } \text{K}$. At an over voltage of $3.1\pm0.2$ V and at $\text{T}=163
\text{ }\text{K}$ we report a number of Correlated Avalanches (CAs) per pulse
in the $1 \upmu\text{s}$ interval following the trigger pulse of
$0.161\pm0.005$. At the same settings the Dark-Noise (DN) rate is
$0.137\pm0.002 \text{ Hz/mm}^{2}$. 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 $\text{T}=233 \text{ }\text{K}$ for a mean wavelength of
$189\pm7\text{ nm}$. At $3.6\pm0.2$ V and $3.5\pm0.2$ V of over voltage we
report a PDE of $13.4\pm2.6\text{ }\%$ and $11\pm2\%$, corresponding to a
saturation PDE of $14.8\pm2.8\text{ }\%$ and $12.2\pm2.3\%$, respectively. Both
values are well below the $24\text{ }\%$ saturation PDE advertised by
Hamamatsu. More generally, the second device tested at $3.5\pm0.2$ 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.
