Milenin, A. P.A. P.MileninRahimi Vaskasi, JavadJavadRahimi VaskasiKazakov, D.D.KazakovShimura, Y.Y.ShimuraKoo, I. G.I. G.KooFerraro, F.F.FerraroDevriendt, K.K.Devriendt2026-07-292026-07-2920262378-0967https://imec-publications.be/handle/20.500.12860/60062<jats:p>We apply the transfer matrix method (TMM) to model the evolution of light spectral reflectivity during reactive ion etching of SiGe heterostructures used in electro-absorption modulators. The simulated reflectivity as a function of etch depth shows excellent agreement with in situ light spectral reflectometry measurements, enabling identification of wavelength ranges most sensitive to changes in the quantum-well (QW) stack. For Ge-rich SiGe (∼80% Ge), both modeling and experiment indicate a sensitivity window centered near 500 ± 50 nm, where the QW heterostructure exhibits a distinct spectral signature. We further show that introducing a thin SiGe etch-contrast layer (ECL) with ∼10% Ge concentration offset from the strain-relaxed buffer composition produces a clear reflectivity response that simplifies end point determination. These results demonstrate how TMM-assisted wavelength selection and ECL engineering can enhance the robustness of etch end point algorithms for advanced SiGe photonic device fabrication.</jats:p>engJournal article10.1063/5.0314383WOS:001786054700001REFLECTOMETRYGROWTH