Investigations On Infrared Optical Characteristics Of Silicon-based Material Based Upon Surface Plasmon

Silicon,one of the most abundant elements in the earth crust,has a lot of excellent characteristics: First of all,Si wafer has good mechanical properties and is easy for fabrication,resulting in a lower-cost compared to other semiconductor materials;secondly,Si material has a relatively large refractive index,and is transparent in the communication waveband,which can be adopted as the transmission waveguide for certain wavelengths;thirdly,silicon photonics technology and mature complementary metal oxide semiconductor(CMOS)technology are highly compatible,and the accumulation of technical experience is sufficient;in addition,the plasma dispersion effect of Si is very significant.Based on it,the Si-based optical modulation technology has achieved breakthroughs constantly.It can be said that Si is the most widely used semiconductor material at present.However,Si cannot absorb the light for wavelengths larger than 1100 nm owing to its large semiconductor bandgap,which severely limits the applications of Si in the infrared range.In order to expand the absorption range of Si material,researchers have proposed the way of fabricating metal micro-or nano-structures on Si's surface to excite the surface plasmon polaritons,which can improve the infrared absorption of Si material.The study of surface plasmon is one of the most popular hotspots in the field of nano-optics in recent years.Surface plasmon polariton is a specific surface wave that propagates along the interface between metal and dielectric,effectively confining the energy into a very thin area.This surface wave not only has possibilities to break the diffraction limit due to its relatively large wave vector,but can cause an obvious field enhancement in the near-field region and realize optical regulation in subwavelength scale.Additionally,surface plasmon polaritons can efficiently produce hot electrons through non-radiative decay in the transmission process,which indicates that the material's absorption range is limited by the Schottky barrier at the metal-dielectric interface instead of its bandgap,offering opportunities to improve the infrared absorption of Si.Therefore,surface plasmon polaritons are able to trigger plenty of applications,including metamaterials,nonlinear optics,solar cell,high integration photonics devices,etc.Compared with other methods,the surface plasmon polaritons based on metal microstructures have many unique characteristics.For example,the frequency and width of the structure's absorption band can be deliberately modulated through shifting its shape parameters,resulting in a designable absorption range;the one-or two-dimensional microstructures can be utilized to respond to the incident light with different polarization.In addition,it is significant to inhibit the losses in plasmonic structures through specific design.According to the above points,this dissertation proposed several Si-based metal micro-or nano structures and predicted their characteristics through simulations,and fabricated these structures by laser direct writing or electron beam lithography to realize the corresponding fuctions.Concretely,the major contents of this dissertation are listed as follows:1.The one-dimensional Si-based metal microstructure is proposed to realize the linear tunable resonance peak.By means of laser direct writing lithography,the one-dimensional grating pattern is prepared on the Si wafer.Then the films are deposited on the sample by magnetron sputtering.Finally,an alternate metal-dielectric multilayer grating structure is obtained.The multilayer configuration can form the Fabry-Perot cavity,resulting in the multiple-mode resonance with a strongly frequency sensitivity.The additional phase shift is calculated by the fitting method,and the calculation results accord well with the simulation results.The relationships between the structure parameters and the experimental results are investigated,and the fabrication errors are discussed.The major resonance orders of this Fabry-Perot mode can be designed to properly distribute in the several major infrared atmospheric windows,which is of great value for application.2.Based on the mode coupling between different surface plasmon polariton modes,the compound one-dimensional grating structure is proposed to realize the loss inhibition effectively.After the pattern preparation by laser direct writing lithography,the trenches are engraved on the sample surface by reaction ion beam etching,and the films are then deposited.The remained multilayer part can excite the Fabry-Perot resonance mode yet,which can be coupled by the additional cavity mode excited in the trench part,resulting in the loss reduction for the whole structure.By analyzing the various parameters of the coupling mode,the relationship between the total and partial losses of the structure is given,providing a new thought to estimate the loss of the compound structure.In the detailed calculation process,the effective mode area is determined by the field integration.Additionally,in the metal-dielectric-dielectric multilayer structure,the field enhancement can be maximized at the quasi-static limit by virtue of the sudden change of the radiation characteristic.This multilayer trench grating structure achieves field convergence and loss inhibition simultaneously,which is crucial to the design for high quality plasmonic devices.3.The narrow or wide absorption band of Si-based material can be realized by the two-dimensional metal structure with the polarization insensitivity.Several two-dimensional structures are proposed,including metal nanoantennas,deep-hole array,and random Ag nanoparticles.The first two structures remain some characteristics of Fabry-Perot resonance,and simultaneously realize the polarization insensitivity.The resonance spectra of the nanoantennas are given through simulations.Because the terminations of the gap waveguide are the equivalent interfaces,the additional phase shifts have some changes,but still can be calculated by the fitting method.Through investigating the deep-hole array structure,the surface plasmon polariton resonance mode based on the asymmetric metal-dielectric-dielectric has been described,resulting in a high absorption spectrum with a wide waveband.The Ag nanoparticle structure with random size and random distribution can be fabricated through the processes of Ag film coating and thermal annealing,and the size of the particle is roughly determined by the annealing temperature.This highly random structure exhibits an ultra-wideband absorption spectrum from 1200 nm to 2500 nm,which is quite distinct from other previous structures.