UV-promoted surface-enhanced Raman spectroscopy via heterojunction of few-layer MoS2 flakes on acceptor-rich β-Ga2O3 microstrips

Surface-enhanced Raman spectroscopy (SERS) by 2D semiconductors relies on chemical (CM) enhancement driven by charge-transfer (CT) processes in bandgap alignment between molecules and substrates. Unfortunately, the low light absorption and weak conferment in the atomic-layer material limit the enhancement factor of Raman intensity (EFRI). Improving the utilization efficiency of excitation light is therefore essential for promoting SERS performance of 2D semiconductors. Here we develop a heterojunction SERS substrate, composed of few-layer MoS₂ (FL-MoS₂) flakes capping onto the acceptor-rich β-Ga₂O₃ microstrips grown by optical vapor supersaturated precipitation (OVSP). The acceptor-rich β-Ga₂O₃ microstrips excited by ultraviolet (UV) irradiation boost the CT processes between FL-MoS₂ and analyte molecules, by which the EFRI was increased by two orders of magnitude up to 9.33 × 10⁴ with the limit of detection (LoD) down to 10^⁻9 M for methylene blue (MB). The in-situ experiment unveils that the SERS improvement is originated from the photoinduced carries trapped by the deep acceptor of Ga²⁻ vacancies (\(\:{V}_{Ga}^{2-}\)) at 2.53 eV below conduction band minimum to facilitate the CT resonance. The present work provides new insights into the role of defect states in the chemical SERS mechanism, demonstrating the improvement of 2D-material substrate performance for ultrasensitive Raman detection.