Enhanced Nonlinear Optical Effect In Semiconductor-Noble Metal Hybrid Nanostructure

Since the 21st century,with the rapid development of microelectronics technology and semiconductor technology,the configuration of optoelectronic devices has been further promoted to ultra-miniaturization and on-chip integration.Under this trend,the research on semiconductor nanomaterials continues to be pioneered and innovated.Semiconductor nanomaterials exhibit many excellent optical and electrical properties,such as high quantum efficiency,high nonlinear susceptibility,and ultra-high photosensitivity.However,as the size of nano-semiconductors decreases,the length of light-matter interaction is compressed.As a result,the optical signal intensity of nano-semiconductors is generally weaker than that of bulk materials.Especially in the most important branch of optics,non-linear optics,even though nano-semiconductors have high nonlinear optical susceptibility,they still cannot compete with the monopoly bulk materials in the application of nonlinear optical devices.How to improve the luminescent efficiency and conversion efficiency of nano-semiconductors is an urgent problem to be solved.Recently,hybrid structures have attracted much attention because of the synergistic effects among their components,which lead to many remarkable properties beyond monomers.And the most typical one is semiconductor-metal hybrid nanostructures.The metal surface plasmon resonance（SPR）or optical microcavity in the hybrid structure has the ability to produce highly confined optical fields and enhance the local-field intensity.Therefore,the interaction between light and nano-semiconductor in the hybrid structure will be greatly boosted.And it results in the improvement of the conversion efficiency and absolute intensity of nonlinear optical signals.In this article,several semiconductor-metal hybrid nanostructures are designed and prepared,which enhances the nonlinear optical properties of nano-semiconductor and promotes its application potential in miniature nonlinear optoelectronic devices.The main content of this paper is as follows:（1）A multifunctional micro-system was designed and built independently.Compared with the commercial system,the system has the characteristics of great flexibility,multiple functions and strong practicability.The system is a confocal microscope,which can be used for time-resolved photoluminescence（TRPL）and transient absorption measurement.We measured the PL spectra,absorption spectra,TRPL,transient absorption spectra and nonlinear optical properties of single Cd S nanowires and monolayer WS₂ by using this system.And the band structure and carrier transition process are analyzed in detail.（2）AnΩshaped Cd S/Mg F₂/Ag hybrid structure was designed and prepared.About1800-time enhancement of two-photon luminescence（TPL）was realized.TRPL and electron dynamics analysis shows that the main reasons for TPL enhancement include:the increase of the two-photon absorption（TPA）caused by the local-field,and the improvement of quantum yield caused by the defect passivation and Purcell effect.Additionally,simulation result indicates the hybrid structure gathers the emitted TPL signal for collection,so the collection efficiency of the objective is also improved.（3）WS₂/TiO₂/Au hybrid structure was designed and prepared.Three orders of magnitude enhancement of second harmonic generation（SHG）was realized.In the ultra-thin hybrid structure（100-nm thick）,the SHG conversion efficiency is as high as 0.02%（single pulse energy of pump light is 62.5 p J）.At the same time,the multi-dimensional regulation function based on this structure is expanded.The chiral or polarization-response of SHG with modulation ratios of 75%and 33%are realized.The physical mechanism of this phenomenon stems from the influence on the local-field intensity by the polarization and chirality of the pump laser.（4）About 189-time enhancement of optical parametric amplification（OPA）is achieved in the WS₂/TiO₂/Au hybrid structure.The OPA enhancement mechanism is the increase of local-field and the coherent superposition of nonlinear optical field in the AA-stack WS₂.The power dependence,polarization and spectra of idle signal from hybrid structure were characterized.In addition,a dual-resonance structure is proposed.According to finite element simulation,5 orders-of-magnitude enhancement of OPA can be achieved in the hybrid structure.And the signal light has a wide tunable range of 800 nm to 2300 nm.