Study On Surface Plasmonic Properties And Applications Of Doped N-type Semiconductors

Surface plasmon(SP)is a type of electrical oscillation,which is excited on the surface between a metal and a dielectric.Surface Plasmon Polaritons(SPP)are electromagnetic excitations propagating at the interface between a dielectric and a conductor;Localized Surface Plasmons(LSP)are non-propagating excitations of the conduction electrons of metallic nanostructures coupled to the electromagnetic field.Surface plasmons attracts lots of attention of researchers because it has the ability of confining electromagnetic field in a sub-wavelength area.Surface plasmon is widely studied in electromagnetic field enhancement and optical devices beyond diffraction limit.In the infrared(IR)range,traditional surface plasmonic materials such as gold and silver have many disadvantages,including difficultly tunable optical parameters,excessive irrational loss and incompatibility with silicon-complementary metal oxide semiconductor(CMOS)process.In this thesis,two n-type semiconductors,transparent conductive oxides(TCOs)and antimony heavily doped germanium are studied as novel potential plasmonic materials which can overcome the disadvantages of tranditonal noble metals in the wavelength ranges of near infrared(NIR)and mid infrared(MIR),respectively.They have unique advantages in plasmonic device,such as tunability,low-loss and compactness of size.Upon above considerations,the thesis is focused on two kinds of surface plasmon applications:transparent conductive oxides based luminescence enhancement in NIR and highly doped germanium based molecular fingerprint chip in MIR.The main contents are listed as bellows:(1).Performance and applications of various n-type semiconductors in IR range are summarized.Based on the dispersion characteristics of real and imaginary part of permittivity of doped semiconductors,combined with their carrier density and mobility,we calculate the figure of merit(QSPP for surface plasmon polariton and QLSPR for local surface plasmon resonance)of several doped semiconductors,metals and graphene.These data provide a basis when select them for different applications in NIR.(2).High-quality Indium Tin Oxide(ITO)films were deposited by magnetron sputtering method.The spectrometer was utilized to obtain their transmittance in Vis-IR waveranges.The permittivity of ITO samples were acquired by parameter fitting based on Drude-Lorentz dispersion model.ITO pillar microcavities were successfully realized by Electron Beam Lithography(EBL)and Inductively Coupled Plasma Etching(ICP)process.We obtained the key process parameters of ITO microstructure manufacturing,and successfully made ITO pillar array whose feature size is around several hundred nanometers.(3).We made a theoretical derivation and simulation of surface plasmon enhanced luminescence in NIR range.The Purcell cavity is formed by ITO microstructure and quantum dot light source.According to different polarizations(p-or s-polarization)of photons which reach the Purcell cavity,we considered two situations in our theoretical analysis and concluded that light emission enhancement of Purcell cavity is sensitive to the size and shape of ITO pillar.The finite-difference time-domain(FDTD)simulation results confirmed the accuracy of our theoretical analysis,and analysed the impact of shape,size and period on luminescence enhancement.Via simulation,it was found that the Purcell cavity could enhance luminescence not only on the top,but also on the side and bottom.Using germanium quantum dots as NIR light source at the wavelength of 1550 nm,the Purcell cavity composed of ITO pillar arrays was measured by photoluminescence to produce around 40%enhancement,compared with those quantum dots without Purcell cavity,where the detector was placed 3.9 mm from top surface.(4).Antimony(Sb)doped germanium(Ge)films with high doping concentrations have been heteroepitaxially grown on silicon substrates with the molecular beam epitaxy(MBE)process.Reflectance of antimony doped n-type germanium epitaxial films were measured by Fourier Transformation Infrared Spectrometer(FTIR).Then their optical parameters were obtained by fitting the reflectance curves.Among them,the carrier density reaches 1.56×1020 cm-3,making the crossover wavelength(where the real part of epsilon equals 0)as short as 4.31 ?m,which broadens the application of germanium materials in MIR range and makes it suitable for MIR plasmonics devices.(5).Bowtie structures composed of two tip-to-tip triangle pillars were designed to excite the localized surface plasmon resonance in MIR.The bowtie microstructures were fabricated by EBL and ICP methods.After spin-coating polymethyl methacrylate(PMMA)film on the surface of the antimony doped germanium chip,the C=O bond vibration signals located around 1800 cm-1 is effectively increased,which agree well with our simulations.In the band from 5.4 to 7.5 ?m,the signal enhancement varies from 2.38 to 5.21.In the manuscript,a Purcell cavity constrcted by ITO nanopillars and NIR light source is proposed,which theoretically proves the feasibility of spontaneous emission enhancement with ITO microcavity in NIR range.The surface plasmonic characteristics of antimony doped germanium is verified with its wide tunable plasmonic frequency,high field enhancement factor in MIR.We also design and fabricate a kind of bowtie array structure of antimony doped germanium for detecting enhanced organic group frequency absorption signals.All above have proved that these two kinds of materials have good application potential in the field of plasmonics in infrared range.