Defect and carrier engineering in Er-doped ZnSe enables synergistic electromagnetic and charge-transfer SERS enhancement

Abstract

Surface-enhanced Raman scattering (SERS) enables sensitive molecular detection, yet conventional substrates often exhibit limited stability and poor reproducibility. Semiconductor substrates offer tunable electronic properties and structural robustness, but wide bandgaps and inefficient charge transfer often hinder their performance. Here, we present interface-engineered Er³⁺-doped ZnSe (Zn_1−xEr_xSe) as a high-performance SERS platform. Controlled Er³⁺ incorporation, with an optimal doping of 6%, introduces defect states that enhance chemical (charge-transfer) mechanisms while increasing carrier density to strengthen the electromagnetic (plasmonic) response. Using methylene blue as a probe, the substrate achieves a detection limit of 3.24 × 10⁻⁸ M with excellent reproducibility. Density functional theory and Mott–Schottky analyses reveal that Er³⁺ doping reshapes the electronic band structure and enables efficient interfacial plasmon–charge coupling. The substrate also demonstrates potential for environmental sensing, achieving a low detection limit of 5.33 µg mL⁻¹ for PET microplastics, thereby highlighting its suitability for trace-level pollutant monitoring. This work establishes rational interface and carrier engineering in semiconductors as a robust platform for high-performance SERS applications in analytical and environmental chemistry.