Tunable Optical Properties Of Semiconductors And Applications In Plasmonics

Surface plasmon polaritons(SPPs)are the modes of propagating electromagnetic wave at the interface between dielectric and conductor,which can confine enery in subwavelength scale and create local field enhancement.The combination of SPP and metamaterials has boosted generation of various new functional devices,such as optical nano antenna,superlens,invisible optical cloak,and can be utilized in communication technology,biological and chemical sens ors,medical imaging,military invisible devices,nanoscale laser,solar cell and many other fields.Semiconductors with low loss have drawn great attention since the hug e loss induced by interband transition in metal.Optical properties of indium tin oxid e(ITO)and other transparent conducting oxides can be tuned by different deposition conditions and external voltage,which can be used to realize active control of SPP.This method will play a vital role in metamaterials and SPP research es and promote the development of active photonic devices.In this thesis,realizing electrostatic modification of ITO and exciation of SPP with lithium niobate(LN)is discussed,and then a method with ITO to tune the epsilon near zero(ENZ)of hyperbolic metamaterials(HMMs)actively is proposed.At last,controlling the SPP propagation in graphene/lithium niobate structure with ferroelectric domain in lithium niobate is discussed by theoretically analysis and numerical simulation.Electrostatic modification at ITO/LN interface by photovoltaic effect of lithium niobate is discussed.First,the photorefractive and photovoltaic effects are explained with single center Kukhtarev model,then the semiconductor interface modification theories are introduced,including the Debye-Huckel model,Thomas-Fermi model,quantum hydrodynamic model and Lindhard theory.Based on the experiment measurements of surface charge accumulation,the variation of ITO permittivity at ITO/LN interface is calculated,along with the photorefractive phase grating in experiment,the dispersion band structure is given and theoretically analyzed with wave-vector matching function.Finally,the reflection and transmission spectra,power dynamic of scattering near surface normal and enery transfer in two beam coupling are discussed under impact of SPP.A hyperbolic metamaterials(HMMs)whose epsilon near zero(ENZ)point can be tuned at visible and near-infrared bands with ITO is designed.The basic properties of HMMs and effective material theory(EMT)by which effective perimittivity can be obtained are introduced in the first part.With the theory,the traditional metal/dielectric structure – Al/Hf O2 and Al/Hf O2/ITO/Hf O2/Al structure with 10 nm ITO are compared about the ENZ shift.The propreties of dual ITO charge accumulation layers can be tuned with different external voltages,so the topological transition points in HMMs,which shifts the ENZ point from near-infrared to visible band.The emergence of ENZ point is explained with EMT and analyzed with ITO property variation under external voltage for the ENZ shift tendency.The wave-vector kz is obtained by transfer matrix method to explain the effect of ENZ on HMMs.A modulator in which controlling the propagation of SPP in ferroelectric material/graphene structure realized by ferreoelectric domain is theoretically and numerically demonstrated.First,the optical property of graphene is introduced,surface conductivity and permittivity with random phase approximation and semiclassial model are compared with contributions from intraband and interband transitions.The surface charge densities of lithium niobate obtained from different methods are compared in the second part.At last,according to the transve rse magnetic dispersion relation in the air/graphene/lithium niobate structure,the SPP lateral penetration depth,ratios between the incident wavelength and lateral penetration,propagation length are analyzed with different graphene chemical potentials.By defining the “on” and “off” states of ferreoelectric domain,comparing the extinction per unit length,modulation depth,power ratio and figure of merit,the optimized length 70 nm of ferroelectric domain can be acquired.This may pave the way for design and application of ferroelectric material/graphene hybrid structure based devices.