Chirality-Driven Second Harmonic Generation and Distinctive Modal Raman Optical Activity in SiC–GeC Quantum Nanodots: A Symmetry-Tuned Pathway

Quantum confinement in heterojunction architectures enable tunable electronic properties and efficient interfacial charge separation, forming a strong basis for next-generation optoelectronics. However, the nuanced interplay between an underlying structural asymmetry, Raman optical activity (ROA), and the nonlinear optical (NLO) signatures─especially under deliberate solvent modulation─remains largely unexplored. Inspired by the recently synthesized honeycomb monolayer of SiC (Phys. Rev. Lett. 2023, 130, 076203), we report the very first extensive analysis of modal Raman optical activity and solvent-driven chirality-driven hyper-Rayleigh scattering (HRS) in 18 distinct quantum dots of SiC, GeC, and isostructural SiC–GeC─spanning 1–3 nm. Focusing on various point group symmetries within this material family, we identify a uniquely chiral SiC–GeC configuration and perform a full ROA study across all relevant scattering geometries and viable experimental conditions. The observation of a low-frequency chiral phonon mode, circular intensity difference signatures, and optical tensor-based handedness descriptors firmly establishes the vibrational origin of a chiral response. Leveraging nonlinear optical effects in such tailored nanostructures is pivotal for next-generation photonic platforms─from quantum information processing to integrated light control. Beyond dynamic higher-order hyperpolarizability profiling, we explore the second harmonic generation through the framework of HRS, revealing strongly polarized symmetry-governed signals characterized by a high depolarization ratio and multipolarity factor. Notably, when these engineered enantiomers are embedded in chiral environments, we observe a markedly enhanced chiral-specific HRS response, pointing to their potential in advancing chiral photonics.