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

We present an experimental method to determine the refractive index of AlxGa1−xAs (x = 0.0–0.5) from 300 to 4 K across the 500–1100 nm wavelength range. The values are extracted from spectroscopically observed microcavity resonances in thin AlGaAs 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 approach yields a quantitatively improved analytical expression for the refractive index n of AlGaAs, achieving modeling accuracy by a coefficient of determination of up to R2 = 0.993, at a maximal experimental uncertainty of Δn = 0.0647. Consequently, it enables accurate modeling in the vicinity of the band edge and revises the quadratic dependence of the refractive index on temperature. The method is straightforward and broadly applicable to other semiconductor systems, offering a valuable tool for the design of microphotonic devices, such as quantum light sources.