Precise Measurement of Refractive Indices in Thin Film Heterostructures

• DOI: 10.48550/arxiv.2301.07712
• Publication Date: 2023-01-01
• Authors: Perner, Lukas W.; Truong, Gar-Wing; Follman, David; Prinz, Maximilian; Winkler, Georg; Puchegger, Stephan; Cole, Garrett D.; Heckl, Oliver H.
• Keywords: Condensed Matter - Materials Science; 0303 health sciences; 03 medical and health sciences; Physics - Instrumentation and Detectors; Materials Science (cond-mat.mtrl-sci); FOS: Physical sciences; Instrumentation and Detectors (physics.ins-det); Physics - Optics; Optics (physics.optics)

We present a robust, precise, and accurate method to simultaneously measure the refractive indices of two transparent materials within an interference coating. This is achieved by measuring both a photometrically accurate transmittance spectrum and the as-grown individual layer thicknesses of a thin-film multilayer structure. These measurements are used for a TMM-based curve-fitting routine which extracts the refractive indices and their measurement uncertainties via a Monte-Carlo-type error propagation. We demonstrate the performance of this approach by experimentally measuring the refractive indices of both, GaAs and Al$_{0.929}$Ga$_{0.071}$As, as present in an epitaxial distributed Bragg reflector. A variety of devices can be used to obtain the transmittance spectrum (e.g., FTIR, grating-based spectrophotometer) and layer thicknesses (e.g., SEM, TEM, AFM), the discussed approach is readily adaptable to virtually any wavelength region and many transparent material combinations of interest. The subsequent model-fitting approach yields refractive index values with $10^{-4}$-level uncertainty for both materials.<br/>13 pages, 3 figures, submitted to PRL<br/>