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

Moritz Langer; Sai Abhishikth Dhurjati; Martin Bauer; Yared Getahun Zena; Ahmad Rahimi; Riccardo Bassoli; Frank H. P. Fitzek; Oliver G. Schmidt; Caspar Hopfmann

paper

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

arXiv:2512.02212

Abstract

We present an experimental method to determine the refractive index of $A l_{x} G a_{1 - x} A s$ (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 $A l_{x} G a_{1 - x} A s$ 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 $A l_{x} G a_{1 - x} A s$ 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.

12 Pages, 9 figures