The Light-mater Coupling And Strain Engineering In Semicondutor Chalcogenide Self-constructed Microcavities

Due to its signicicant restriction of electromagnetic field,semiconductor microcavity has drawn increasing attention in studying the coupling between light and matter.Especially,for some semiconductor materials with specific surface morphology features,they not only can be used to form the optical resonator but also has good gain characteristics,making them very beneficial to explore the basic physics in coupling between light and matter,and the potential application value in optoelectronic devices.As a kind of typical direct wide bandgap material,II-VI semiconductor materials have rich morphological characteristics,large exciton binding energy and strong oscillator strength,which makes them are perfect vectors to study the coupling between light and matter.Among them,CdS has significant applications in optoeletronic devices,such as nanometer laser,optical detection and waveguide devices.Recently,since graphene was first deposited by mechanical exfoliation in 2004,transition metal sulfides(TMDs),as layered structure materials,back into our research scope.At the moment,researches reported have confirmed that TMDs has large exciton binding energy and strong oscillator strength,undoubtedly,it would add new energy into studying physical mechanism of the interaction between light and matter.Furthermore,we find that the modulation method about coupling between light and matter is limited.In most cases,researchers achieved the purpose of regulation by changing temperature,electric field,magnetic field or the size of sample.However,because of the limited adjustable range and relatively high requirement of experimental equipment,these methods extremely limit the development of further applications.Along with the "Elastic strain engineering" was put forward,the modulation action of stress in electrics and optics of materials has received intensely investigation.While,there are few reports about the modulation effect in coupling between light and matter.Therefore,aiming at the above problems and research situation,this thesis will discuss the interaction between light and matter in different materials,and the modulation of the strain on the coupling effect.The primary contents of this thesis are as follows:Firstly,in order to improve the spatial resolution of spectral measuring for nanomaterials,we designed and built a spectrum measurement system of micro-area based on single-mode fiber and microscope system.The system can realize three functions,the measurements of reflection spectrum,fluorescence spectrum and angular resolution spectrum.Among them,the former two are realized by putting a single-mode fiber,as field stop,on the seconda ry image plane,resulting in the spatial resolution in sub-microns,and the latter one can get the dispersion relation of semiconductor materials by taking photographs at one-time.Secondly,we select tungsten disulfide(WS2),one of the representative materials of transition metal sulfides,as research model to study the coupling between Fabry Perot(F-P)microcavity modes and excitons in layered structure materials.The WS2 nanoflakes with different thicknesses are prepared by mechanical exfoliation.Atomic force microscope(AFM)was used to select nanoflakes in suitable thicknesses,so as to adjust the detuning between self-constructed F-P microcavity,formed between the upper and lower surface of nano flakes,modes and excitons in WS2.The anti-crossing behavior between cavity mode and excitons with flake’s thickness dependence is directly observed experimentally.Moreover,based on the coupled oscillator model,we studied the dispersion relation of exciton polaritons and figured out the Rabi splitting of A and B excitons.The accomplishment of this work will provide a new approach for the research on strong coupling effect of layered structure materials.Thirdly,we put forward a new method to prepare cyclic buckled CdS nanowires and nanoribbons,the method is simple and sample obtained is stable.Under different polarizations,we explored the modulation of emission energy in different single buckled CdS nanostructures,and confirmed that the strain modulation of emission features in different structures correspond to different physical mechanisms.We also studied the dynamics of excitons under tensile strain,and found that the increase of energy splitting between A and B exciton will increase the life time of A excitons and decrease the life time of B excitons,this phenomenon will provide an effective way to improve the performance of optoelectronic devices.Finally,we studied the microcavity and lasing properties of CdS nanoribbons.Based on the strain engineering,the lasing properties of buckled CdS nanoribbons is presented for the first time,in witch,the strain dominated mode selected in multi-mode laser and neligible mode shifts in single mode laser are clearly observed.By combining the Young’s interference method together with angle-resolved microphotoluminescence spectral technique,we directly observed the parity of the lasing modes.These results show that the strained nanoribbons may serve as new functional optical elements for flexible light emitter or on-chip all-optical devices.