Temperature-dependent refractive index of AlGaAs for quantum-photonic devices near the bandgap

TL;DR

This paper introduces an experimental method to accurately determine the temperature-dependent refractive index of AlGaAs across a broad wavelength range, crucial for designing quantum photonic devices at cryogenic temperatures.

Contribution

It provides a novel, precise measurement technique and refined models for the refractive index of AlGaAs, improving device simulation accuracy near the bandgap at low temperatures.

Findings

Refractive index varies significantly with temperature and composition.

Derived analytical expression matches experimental data with R^2=0.993.

Method is applicable to other semiconductor systems.

Abstract

We present an experimental method to determine the refractive index of $Al_{x}Ga_{1-x}As$ (x = 0.0 - 0.5) from 300 K to 4 K across the 500 - 1100 nm wavelength range. The values are extracted from spectroscopically observed microcavity resonances in thin $Al_{x}Ga_{1-x}As$ membranes embedded between fully and partially reflective gold mirrors. Refined Varshni and Paessler models are used to describe temperature-dependent bandgap shifts and material composition. By tracking resonance shifts and benchmarking against finite-difference time-domain simulations, we derive the dispersive optical response with high precision. This yields a quantitatively improved analytical expression for the refractive index of $Al_{x}Ga_{1-x}As$ matching the experimental results with a coefficient of determination as high as $R^2=0.993$, enabling accurate modeling near the band edge at cryogenic temperatures. The method is straightforward and broadly applicable to other semiconductor systems, offering a valuable tool for the design of micro photonic devices such as quantum light sources.