Reflectance of Silicon Photomultipliers at Vacuum Ultraviolet Wavelengths

TL;DR

This study measures the VUV reflectance of silicon photomultipliers (SiPMs) from two manufacturers, analyzing angular dependence and optical constants to improve understanding for liquid xenon detector applications.

Contribution

It provides the first detailed characterization of VUV reflectance and optical constants of SiPMs, including angular dependence and diffuse reflectance measurements.

Findings

Refractive index and extinction coefficient of silicon dioxide on SiPMs are derived.

Angular dependence of specular reflectance is characterized.

Reflectance data is used to predict behavior in liquid xenon environments.

Abstract

Characterization of the vacuum ultraviolet (VUV) reflectance of silicon photomultipliers (SiPMs) is important for large-scale SiPM-based photodetector systems. We report the angular dependence of the specular reflectance in a vacuum of SiPMs manufactured by Fondazionc Bruno Kessler (FBK) and Hamamatsu Photonics K.K. (HPK) over wavelengths ranging from 120 nm to 280 nm. Refractive index and extinction coefficient of the thin silicon-dioxide film deposited on the surface of the FBK SiPMs are derived from reflectance data of a FBK silicon wafer with the same deposited oxide film as SiPMs. The diffuse reflectance of SiPMs is also measured at 193 nm. We use the VUV spectral dependence of the optical constants to predict the reflectance of the FBK silicon wafer and FBK SiPMs in liquid xenon.