Theoretical Studies On Stokes Raman Scattering Of Low-dimension Semiconductors

Nano-semiconductors have caused widespread concern and become a hot spot of thestudy in materialogy. The low dimensional semiconductor is a new kind of semicon-ductor material that is artificial, and has plenty of new phenomenon and e?ects,whichare very di?erent from bulk materials. With the dimension and the feature size reduc-tion, the quantum interference e?ect, quantum tunneling e?ect, Coulomb blockade e?ect,many-body correlation and nonlinear optical e?ect etc. of low dimensional semiconductorsystems become more and more obvious. These new properties not only lead to the sig-nificance theoretical research, but also open the way to develop new generation quantumdevices(quantum interference transistor, quantum field-e?ect transistor, single-electrontransistor, single electron memory, quantum dot laser, and microcavity laser). With theinformation era coming, the information manufacturing industry has become one of thepillar industries in the country. Therefore, it is urgent for people to understand physicalproperties of these structures. Since Indian physicist C.V. Raman observed the scatteringphenomenon in 1928, Raman scattering has been usually applied in various fields. Ramanscattering, due to using photonic probe, has advantages of convenience and no damage tothe materials being measured. It has become one of the most e?ective methods to studystructure of crystals or molecules. In this paper,within the framework of the e?ective-mass approximation , theoretical studies are presented on Raman scattering in rectangularquantum wires and in cylindrical quantum dot associated with phonon modes. ElectronRaman scattering also is discussed in harmonic oscillators quantum wire with an appliedelectric field. The dissertation includes five chapters:In the first chapter, a simple introduction to the theory of Raman scattering within theframework of the e?ective-mass approximation used throughout this paper is presented.A current research and application of Raman scattering is summarized brie?y.In the second chapter, phonon modes assisted Raman scattering in rectangular quan-tum wires is studied under the dielectric continuum model. Using the third-order pertur-bation method,the di?erential cross section and the selection rules are presented. Wefound that Raman scattering for antisymmetric optical phonon modes is forbided. Thepositions of the ingoing resonance peaks are consistent, but the positions of the outgoingresonance peaks depend on phonon modes frequencies. Raman spectrum for longitudinaloptical (interface optical) phonon modes appears a red shift with the size increasing. Thecontribution of interface optical is significant in small-size quantum wires, while for large size, longitudinal optical phonon modes play more important role in Raman scattering.Raman scattering is sensitive to the variation in size for quantum wires of square crosssection.In the third chapter, Raman scattering associated with phonon modes is investigatedin cylindrical quantum dot. The selection rules are given. Numerical results and discus-sions are presented for di?erent dot sizes, and various phonon modes. The results indicatethat the contribution of antisymmetric interface phonon modes is much smaller than thatof symmetric interface phonon modes. The size have an important e?ect on the contribu-tions to the di?erential cross-section (DCS)for phonon modes. The contributions to theDCS for the symmetric side interface optical phonon modes are larger than that for thelongitudinal optical phonon modes in small-size quantum dots, while for large quantumdots, the Raman scattering for longitudinal optical are significant.In the fourth chapter, Electron Raman scattering is investigated in harmonic oscil-lators quantum wire with an applied electric field. Numerical calculations of DCS areperformed. The results indicate that the stronger the external electric field is, the smallerthe peak value is. Under a constant external electric field, the harmonic oscillator fre-quency and the applied electric field intensity have an e?ect on the peak value, and theharmonic oscillator frequency which is perpendicular to the direction of electric field haveimpact on the position of the peak.In the last chapter, a brief summary about the theories and the main results is given.The shortage and further research are also mentioned.