Semiconductor-based surface-enhanced Raman scattering (SERS) substrates have emerged as a promising alternative to traditional metallic SERS platforms, offering tunable optical properties, enhanced stability, and unique charge-transfer mechanisms. While noble metals like gold and silver dominate conventional SERS due to their strong plasmonic response, semiconductors provide distinct advantages in terms of cost, reproducibility, and multifunctionality. The enhancement mechanisms in semiconductor SERS substrates arise from both electromagnetic and chemical contributions, with nanostructuring playing a critical role in optimizing performance.

Enhancement mechanisms in semiconductor SERS substrates differ from those in metallic systems. Electromagnetic enhancement in semiconductors is typically weaker than in metals due to their lower free-carrier concentrations, but certain wide-bandgap semiconductors like ZnO, TiO2, and SiC can support localized surface plasmon resonances when doped or defect-engineered. For example, aluminum-doped ZnO nanostructures exhibit plasmonic behavior in the visible and near-infrared regions, enabling electromagnetic enhancement factors of 10^3 to 10^4. Chemical enhancement, on the other hand, often dominates in semiconductors due to their rich surface chemistry and charge-transfer interactions with analyte molecules. This mechanism involves resonant energy transfer between the semiconductor’s electronic states and the molecular orbitals of the adsorbate, leading to additional Raman signal amplification. The combined effect of both mechanisms can yield total enhancement factors comparable to those of metallic substrates in select cases.

Nanostructuring is essential for maximizing SERS performance in semiconductor systems. Hybrid structures combining semiconductors with metallic nanoparticles, such as Au/ZnO heterostructures, leverage the plasmonic properties of metals while benefiting from the semiconductor’s charge-transfer capabilities. In such systems, the metal nanoparticles provide strong electromagnetic hotspots, while the semiconductor facilitates chemical enhancement through interfacial electron transfer. For instance, Au-decorated ZnO nanorods demonstrate enhancement factors up to 10^6, attributed to synergistic plasmon-exciton coupling and efficient charge separation. Pure semiconductor nanostructures, such as silicon nanopillars or porous silicon, also exhibit significant SERS activity due to their high surface area and light-trapping capabilities. Black silicon, with its needle-like surface morphology, enhances Raman signals by both increasing the adsorption sites and improving light absorption through multiple scattering events.

Applications of semiconductor SERS substrates span molecular detection in environmental monitoring, biomedical diagnostics, and chemical sensing. Their biocompatibility and chemical stability make them suitable for in situ analysis of biological molecules, such as proteins, DNA, and pharmaceuticals. For example, TiO2-based SERS substrates have been used to detect dopamine at nanomolar concentrations, leveraging the material’s photocatalytic properties to enhance signal reproducibility. Semiconductor SERS platforms also show promise in detecting hazardous substances, including pesticides and heavy metal ions, due to their selective adsorption properties. In contrast to metallic substrates, semiconductors often exhibit better signal uniformity and lower background interference, which is critical for quantitative analysis.

Comparisons between semiconductor and metallic SERS substrates reveal trade-offs in performance and applicability. Metallic substrates, particularly those made of Ag or Au, generally provide higher enhancement factors (10^6 to 10^8) due to their intense plasmonic resonances. However, they suffer from drawbacks such as poor thermal stability, oxidation susceptibility, and high cost. Semiconductor substrates, while typically offering lower enhancement factors (10^3 to 10^6), excel in environments where metals degrade, such as high-temperature or chemically aggressive conditions. Additionally, semiconductors enable more predictable molecule-substrate interactions due to their well-defined surface chemistry, reducing the variability often encountered with metal surfaces. The ability to engineer semiconductor bandgaps and defect states further allows customization of SERS response for specific analytes, a feature less accessible in metallic systems.

Recent advances in semiconductor SERS focus on optimizing nanostructure design and hybrid material systems. Core-shell configurations, where a semiconductor encloses a metal core, balance electromagnetic and chemical enhancement while protecting the metal from environmental damage. Another approach involves using two-dimensional materials like MoS2 or graphene as SERS-active platforms, where their atomic thickness and high surface-to-volume ratio enhance charge-transfer interactions. Doping strategies, such as nitrogen-doped graphene or sulfur-doped ZnO, further refine the electronic structure to improve Raman signal amplification. These innovations position semiconductor SERS substrates as versatile tools for next-generation sensing applications, complementing and in some cases surpassing the capabilities of traditional metallic systems.

In summary, semiconductor-based SERS substrates offer a compelling combination of tunability, stability, and multifunctionality, addressing limitations inherent to metallic platforms. Their dual enhancement mechanisms, coupled with advanced nanostructuring techniques, enable sensitive and reproducible molecular detection across diverse fields. While metals remain the gold standard for maximum enhancement, semiconductors provide a robust alternative for applications demanding durability, selectivity, and tailored performance. Continued research in material engineering and hybrid designs will further expand the utility of semiconductor SERS in analytical science and technology.