only have attributes of both components, but promises to exhibit new properties, which would be difficult to achieve using each component separately. Plasmonic materials are popular for use in applications and research because they have excellent light absorption cross-section, high electron concentration, and it is possible to tune the resonance wavelength by altering their shape, size, and the environment. Optimized coupling between nanoplasmonics and semiconducting materials can enhance and

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... omplement the efficiency of almost all the semiconductor technologies of lasers, solar cells, detectors, sensors, imaging, and electronics. It has been demonstrated that introducing the nanoplasmonics local fields into semiconductor devices enhances the light coupling to nanowires, [1, 2] increases photocurrent in germanium detectors, [3] provides means for terahertz all-optical switching, [4] enables sub-gap detection using gold nano-antennas on silicon, [5] allows DNA detection, and [6] produces large non-linearity in epsilon-nearzero material [7] and metasurfaces. [8] et, despite considerable research interest and technological impact, the tailored fabrication of composite material, comprised of a semiconductor with embedded plasmonic nanoparticles, remains a formidable challenge. The conventional mixing techniques used for combining non-conductive dielectrics with metal particles -such as sol-gel, metal-dielectric co-sputtering, metal-ion implantation and pulsed laser deposition, have not been developed to a satisfactory level for semiconductor/metal composites to assure uniformity over metal particles size and density. The lack of the established fabrication techniques hampers the investigation of the plasmon field influence on the charge carrier generation, distribution, decay, and linear and non-linear properties in the semiconductors with embedded clusters supporting the localized surface plasmon (LSP) field. We attempted to resolve this deficiency and develop a method to fabricate nanoplasmonic-semiconductor composite. We deployed the immersion-plating method to spontaneously grow gold clusters inside nano-porous silicon (np-Si). Although this method is not new, the vast majority of the formerly works employed it to pin metallic particles to the surface. This study is different in that the optical properties and effects of the LSP excitation were investigated for a composite semiconducting material with metallic particles embedded uniformly across its volume. Embedding particles in the volume allows more degrees of freedom to design applications Coupling between nanoplasmonics and semiconducting materials can enhance and complement the efficiency of almost all semiconductor technologies. It has been demonstrated that such composites enhance the light coupling to nanowires, increase photocurrent in detectors, enable sub-gap detection, allow DNA detection, and produce large non-linearity. Nevertheless, the tailored fabrication using the conventional methods to produce such composites remains a formidable challenge. This work attempts to resolve that deficiency by deploying the immersion-plating method to spontaneously grown gold clusters inside nano-porous silicon (np-Si). This method allows the fabrication of thin films of np-Si with embedded gold nanoparticles (Au) and creates nanoplasmonic-semiconductor composites, np-Si/Au, with fractional volume between 0.02 and 0.13 of the metallic component. Optical scattering measurements reveal a distinctive, 200 nm broad, localized surface plasmon (LSP) resonance, centered around 700 nm. Linear and non-linear properties, and their time evolution are investigated by optically pumping the LSP resonance and probing the optical response with short wavelength infra-red (2.5 µ µm) light. The ultrafast time-resolved study demonstrates unambiguously that the non-linear response is not only directly related to the LSP excitation, but strongly enhanced with respect to bare np-Si, while its strength can be tuned by varying the metallic component.