| In order to make optoelectronic products tend to miniaturization and integration,researchers continue to expand the study on new materials on the basis of silicon semiconductors.Two-dimensional materials,due to their unique photoelectric,thermal,magnetic and mechanical properties,have gradually become the forefront of scientific research.As a typical representative of two-dimensional materials,graphene has excellent characteristics such as controllability,ultra-high carrier mobility,bipolar behavior,quantum Hall effect,superconductivity and van Hove singularity,which make it one of the potential candidate for future nano-optoelectronic devices.At present,there are many kinds of graphene-based optoelectronic products,such as field effect transistors,photodetectors,gas sensors,etc.However,due to the lack of band gap,graphene material can’t meet the large enough switching ratio of logic devices and the conduction current of transistors.Its application in logic devices is greatly limited.Therefore,looking for other "graphene-like" two-dimensional materials to make up for this defect has become another hot research topic.Elements such as silicon,germanium and tin,which are in the same IVA group with carbon,have similar electronic structures.These elements can form two-dimensional materials with one-atom thickness,just similar with graphene,and all of them have unique physical and chemical properties.Due to the buckling in the structure of silicene,germanene and stanene,they have more advantages in the integration with the substrates.Recent studies have shown that the band structure of silicene can be manipulated by external transverse electrostatic field.Because the carrier is weakly coupled with the in-plane phonons,and the presence of buckling structure,the intrinsic carrier mobility of germanene is significantly higher than that of silicene.Because of its strong spin-orbit coupling effect,stanene has some special properties at room temperature,such as topological insulation effect,thermoelectric effect,topological superconductivity,abnormal quantum Hall effect and so on.Therefore,silicene,germanene and stanene have attracted more and more attention.It is expected to develop the next generation of optoelectronic products with excellent performance for driving,detecting,sensing,storage and energy conversion based on these graphene-like materials.However,their applications in semiconductor and optoelectronic industries are limited due to the disadvantages of preparation technology and the instability at room temperature.At present,the focus research on graphene is the design of optoelectronic devices with more excellent performance;For silicene,germanene and stanene,because of its preparation methods is not perfect,the properties of themselves still need to be further studied.In present thesis we studied the optical properties of silicene/germanene/stanene-substrates,and then based on these results we studied and designed photoelectric devices.It provides a theoretical basis and development idea for the next generation of optoelectronic products.The contents of this thesis mainly include the following aspects:1.Ultra-sensitivity refractive sensor based on graphene material at mid-infrared wavelengthsA kind of configuration of tunable diffractive grating based on mono-and multi-layer graphene material working at mid-infrared wavelengths is presented in this thesis.The structure consists of silica deposited on silicon substrate periodically and graphene material deposited on silica.This configuration has an extremely strong absorption at particular wavelength in mid-infrared region.At the same time,the resonance wavelength shifts dramatically with a slight variation of the doping concentration of the graphene ribbons.A potential application of the diffractive grating is as a sensitive sensor for surrounding environment refractive index.The sensitivity up to 7370nm/RIU can be achieved and it’s the highest sensitivity among refractive sensors investigated before to our best knowledge.This research paves the way towards ultra-sensitive sensor devices at mid-infrared wavelengths and make the most of the advantage in biosensing,gas detection and so on.2.Ultrahigh-efficiency enhanced four-wave-mixing in Si-Ge-Graphene photonic crystal waveguideCompared with optical-electrical-optical signal processing widely applied nowadays,all-optical processing has a huge superiority in speed and efficiency.A waveguide composed of silicon with mono-layer graphene coated as core and Si-Ge distributed periodically on both sides as cladding is proposed in the present thesis.The graphene can excite localized surface plasmon polaritons and the cladding can decrease the propagation loss.Both factors contribute to the enhancement of four-wave-mixing process.The conversion efficiency can be increased by 16 d B compared with silicon waveguide.The existence of graphene can enhance the electric intensity and the Si-Ge Bragg structure cladding can decrease the propagation loss as small as 0.032 d B/cm.This configuration offers a new physical mechanism and solution for all-optical signal processing and high efficiency nonlinear nanoscale devices.3.Optical properties of silicene-dielectric interfacesAs a two-dimensional "graphene-like" material,silicene becomes a candidate that can make up for the deficiency of graphene.Compared with graphene,the band gap of silicene is adjustable under the condition of external transverse electrostatic field.At the same time,the compatibility and integration of silicene are more advantageous in the application of nanometer devices based on silicon nanotechnology.The complex surface conductivity is applied to characterize the properties of silicene and the optical characterization of silicene-dielectric interfaces from IR to far UV range is investigated in this thesis.The silicene-Si and silicene-Ge interfaces along both parallel(TM)and perpendicular(TE)polarization directions of electromagnetic field with normal incidence are considered.The calculation results show that the reflectivity and transmission are all sensitive to the UV wavelength and the absorption is ultra-high.While in the IR range,the reflectivity and transmission will reach a relatively constant value.In the silicene-Si structure,the reflectivity and transmission constant value in the IR range are 31% and 69% respectively.Likewise,the constant value of reflectivity and transmission are 37% and 63% respectively in silicene-Ge interfaces.The absorbance of different systems in the case of TE polarization is significantly lower than that of TM polarization.When the wavelength is larger than 0.5μm,the reflectivity of the silicon substrate can be significantly increased and the transmittance can be decreased.Silicene can significantly increase the reflectivity of the germanium substrate from infrared to ultraviolet,but the effect of reducing the transmittance is stronger in the infrared wavelength.This study explores the potential applications of silicene as sensors,detectors,filters and ultraviolet absorbers in the optoelectronic industry.4.Optical properties of germanene-metal interfacesGermanene is also a kind of "graphene-like" two dimensional material.It becomes the focus of nano-sheet research in recent years because of its ultra-high intrinsic carrier mobility which can meet the requirements of future nano-optoelectronic devices.The band gap of germanene at the Dirac point is significantly higher than that of graphene and silicene.Thus germanene can realize quantum Hall effect at higher temperature.At the same time,it has a wide application prospect in logic devices such as field effect transistors and optoelectronic spin devices due to its adjustable band gap.The optical characteristics of germanene-metal interfaces from IR to far UV are studied in this thesis.The properties of germanene are characterized by the complex surface conductivity.It’s shown that when the TM polarization plane wave is incident to germanene-Ag interfaces,the absorption in UV region is obviously higher than that of TE polarization.The higher absorption band is located in the different wavelength.In TM polarization,the higher absorption band is ultraviolet whereas in TE polarization it’s visible light.This result can be used in practice that different bands can use different polarizations to absorb it.In both cases,germanene can significantly enhance the reflectivity of silver substrate close to 100%,but the wavelength at 100% reflection under TM polarization is smaller than that of TE polarization,and the enhancement factor is stronger.In addition,germanene can also reduce the absorption of the silver substrate to nearly zero in the infrared wavelength.5.Perfect absorber based on staneneStanene is a kind of two-dimensional structural material of the Sn in group IVA.As a graphene-like 2D material,its high spin-orbit coupling property has attracted extensive attention from researchers.Substances with high absorption properties are of great significance in many fields of science and technology,and the perfect absorber at micro/nano scale can be widely used in photoelectric detector,thermal imaging,solar thermal photovoltaic conversion emitter,anti-reflection coating and microthermal radiometer,etc.In this thesis,a perfect absorber based on stanene is designed and studied.The structure consists of the top stanene layer,the middle dielectric layer and the bottom Au substrate.The properties of stanene is characterized by complex surface conductivity model.The results show that the absorbance of the perfect absorber is about 99.95%.The effects of refractive index and thickness of dielectric layer on absorbance are also studied.The increase of former case causes the resonance wavelength of the perfect absorber redshifted,whereas the increase of latter case causes the resonance wavelength blueshifted.At the same time,the perfect absorber is insensitive to the angle of incident light.The extremely high absorbance is achieved in the wide angle range of 0～40°. |
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