Dry-Ice-Bath Anodization of Heavily Boron-Doped Silicon: A Physically Controlled Process for Creating Quantum-Confined Nanostructures

• A temperature-controlled anodization design via a physical pathway was developed based on material properties in electrochemical etching. • Dry-ice-bath anodization at -20°C provides a simple route for uniform anodization of heavily boron-doped positive-type silicon, producing 3–4 nm nanocrystals with strong red photoluminescence emission. • Structural transition from mesoporous to microporous morphology enhances photoluminescence emission in heavily doped silicon through quantum confinement. We report and implement a temperature-controlled design that modulates material reactivity via electrochemical processing to fabricate silicon nanostructures. The resulting structures exhibit quantum confinement-induced photoluminescence (PL), a critical characteristic for realizing silicon photonic devices on heavily boron-doped silicon. This effect is achieved simply by lowering the electrolyte temperature to -20°C via a dry-ice bath. The temperature-oriented design effectively alters the interfacial reaction dynamics and overcomes the doping concentration-induced limitations in nanostructuring heavily boron-doped silicon, enabling stable PL without post-oxidation or modification of the intrinsic material properties. Typically, anodization of heavily boron-doped silicon at room temperature produces a black, velvet-like mesoporous surface that absorbs incident light and exhibits no PL; in contrast, anodization at -20°C generates a distinct bright red emission under UV illumination. Transmission electron microscopy revealed the formation of silicon nanocrystals approximately 3–4 nm in size, which are responsible for the observed quantum confinement. Moreover, the etching behavior at -20°C is predominantly isotropic, whereas at room temperature, it becomes anisotropic. This study establishes low-temperature electrochemical processing as a versatile and scalable route for tailoring semiconductor nanostructures, thereby broadening the applicability of silicon-based quantum-dot technologies.