Plateau–Rayleigh Instability–Driven Shell-First Growth of (Ge, Si1– x Ge x )–AlN Core–Shell Crystals Exhibiting Telecom E-Band Photoluminescence

Abstract Si and Ge are technologically important semiconductors for electronic, photovoltaic, and optoelectronic applications. Herein, we report mixed-source hydride vapor phase epitaxial growth of (Ge, Si1–xGex)–AlN core–shell crystals on Al-based nanoabsorbers. Nano-CT and microscopy resolve hollow, partially filled, and filled morphologies that together support a Plateau–Rayleigh-instability-mediated shell-first model in which an Al-derived shell-like structure precedes filling by Ge-containing or Si–Ge-containing material. Electron microscopy, energy-dispersive X-ray spectroscopy, and Raman measurements provide complementary structural and compositional context, including local observations consistent with 2H-like Si domains. Four room-temperature photoluminescence spectra recorded under 532 nm excitation show telecom E-band features with sampled maxima at approximately 1371.9, 1377.0, 1381.1, and 1391.8 nm. Additional archived nominal-setting records for four spectral windows are presented as qualitative excitation-setting comparisons. Audited HSE Δ-self-consistent-field end points and PBE scaling calculations evaluate neutral CSi–Oi as a candidate model, while newly added formation, association, k-point, and cell-size sensitivity tests define the scope of that comparison. The optical data are therefore reported without a peak-specific microscopic or single-emitter assignment. The combined results establish the shell-first growth morphology and document room-temperature E-band photoluminescence in group-IV/III-nitride core–shell material.