  Silicon photomultipliers are regarded as a very promising technology for
next-generation, cutting-edge detectors for low-background experiments in
particle physics. This work presents systematic reflectivity studies of Silicon
Photomultipliers (SiPM) and other samples in liquid xenon at vacuum ultraviolet
(VUV) wavelengths. A dedicated setup at the University of M\"unster has been
used that allows to acquire angle-resolved reflection measurements of various
samples immersed in liquid xenon with 0.45{\deg} angular resolution. Four
samples are investigated in this work: one Hamamatsu VUV4 SiPM, one FBK VUV-HD
SiPM, one FBK wafer sample and one Large-Area Avalanche Photodiode (LA-APD)
from EXO-200. The reflectivity is determined to be 25-36% at an angle of
incidence of 20{\deg} for the four samples and increases to up to 65% at
70{\deg} for the LA-APD and the FBK samples. The Hamamatsu VUV4 SiPM shows a
decline with increasing angle of incidence. The reflectivity results will be
incorporated in upcoming light response simulations of the nEXO detector.

Instrumentation and Detectors