Monte Carlo Calculations of the Extraction of Scintillation Light from Cryogenic N-type GaAs

TL;DR

This study uses Monte Carlo simulations to explain the high scintillation luminosity of cryogenic n-type GaAs, suggesting optical scattering and low absorption are key factors, aiding dark matter detection design.

Contribution

It provides a detailed Monte Carlo model of optical scattering and absorption in cryogenic GaAs, offering insights for optimizing scintillation detectors for dark matter research.

Findings

High luminosity explained by optical scattering rather than absorption

Simulation of 16 surface reflector configurations for detector design

Guidelines for measuring optical properties at cryogenic temperatures

Abstract

The high scintillation luminosity of n-type GaAs at 10K is surprising because (1) with a refractive index of about 3.5, escape is inhibited by total internal reflection and (2) narrow-beam experiments at 90K report infrared absorption coefficients of several per cm. This paper presents Monte Carlo calculations showing that the high luminosity at 10K can be explained if (1) narrow-beam absorption is almost all optical scattering and (2) the absolute absorption coefficient is below 0.1 per cm. Sixteen surface reflector configurations are simulated for a range of internal scattering and absolute absorption coefficients, and these can guide the design of cryogenic scintillating GaAs targets for the direct detection of dark matter. The discussion section presents a possible infrared scattering mechanism based on the metallic nature of n-type GaAs. Appendix A describes the Monte Carlo program steps in detail. Appendix B shows how narrow-beam and integrating sphere experiments can measure the cryogenic optical scattering and absolute absorption coefficients.