Excitonic Effect On Raman Scattering In Quantum Dots

With the development of nano-technology,the dimension of semiconductor has been reduced,and photoelectric devices have received intense attention.Quantum wires,quantum rings,quantum wells and quantum dots have been used to manufacture optoelectronic devices.Compared with the traditional semiconductor material,the binding energy of the carriers?such as electrons,holes,excitons,etc.?can be increased in a low dimensional system.And the nano-semiconductors have higher work speed,wider energy band and higher photochemical inversion rate than the traditional semiconductors.In order to study the photoelectric properties of low dimensional semiconductor materials,Raman scattering is introduced to study the optical properties and band structures of low dimensional semiconductor materials,which is helpful to the innovation of new optoelectronic materials.In the first chapter,the background and significance of this study are briefly described.The research methods of Raman scattering in low dimensional semiconductors,the application of nitride heterostructures,and the optical process of excitons in low dimensional semiconductors are introduced.In the second chapter,Differential Cross Section?DCS?has been investigated theoretically for the Raman scattering in ln_xGa_1-xN/GaN quantum dot?QD?within the frame work of effective-mass approximation at T=0K.Numerical calculations reveal that the built-in electric field has a significant influence on the DCS.Raman shifts are observed by making a change to the In mole fraction x and parabolic frequencies.With the increase of the built-in electric field,the full width at half maximum?FWHM?of spectrum decreases.In the third chapter,the exciton states in ln_xGa_1-xN/GaN quantum dot?QD?within the frame work of effective-mass approximation at T=0K.Using the variational method,the wave function and the eigen states of the exciton was derived.A series of Raman scattering spectra are obtained by theoretical calculation,and the influence of the excitonic effect on the Raman scattering is studied by changing the height,radius and molecular component of the quantum dot.In the fourth chapter,a theoretical calculation of the DCS is presented for the exciton-mediated Stokes Raman scattering in CdS quantum dot within the frame work of effective mass approximation at T=0K.Numerical calculations reveal that the excitonic effects cause blue shifts in Raman spectroscopy.The magnitude of the Raman shift depends on the quantum confinement,the Coulomb interaction,and the incident photon energy.