Unraveling Sub-Nanostructure Variability in Amorphous Silicon: Mechanisms of Short-Range Order and Defect Dynamics via In Situ Raman Spectroscopy

Quantitatively probing sub-nanometer elementary structural units of amorphous materials, such as amorphous silicon (a-Si), is essential for Si-based technological progress. However, accurately identifying and quantifying short-range order (SRO) and dangling bond/floating bond (DB/FB) defects over a large area in a-Si remains largely unexplored. Here, it is demonstrated that both the SRO and DB/FB defects at the sub-nanometer scale can be quantitatively characterized using Raman spectroscopy. Multi-wavelength lasers (450, 514, and 635 nm) are employed to modulate the sub-nanometer structures in a-Si films. Using in situ and ex situ Raman spectroscopy, structural evolution is tracked and changes in the Raman band at ∼ 480 cm⁻¹ (ω₄₈₀) are investigated. These results reveal distinctly different effects of DB and FB defects on ω₄₈₀, which arise from defect-induced interfacial stress changes at the Continuous Random Network (CRN)-SRO interface. An analytical model is established to extract SRO dimensions and DB/FB defect densities from Raman spectra. These research findings deepen the understanding of sub-nanometer scale structures in amorphous materials and provide crucial methodological foundations for structural characterization and property modulation, showing promise for performance optimization and breakthroughs in amorphous material-based optoelectronic devices, especially those integrated with Si-based structures for cutting-edge applications.