Studies On Nonlinear Optical Properties And Hydrogenic Impurity States In Quantum Wells And Dots

Thanks to the advances of nanofabrication techniques, it is possible to produce Lowdimensional semiconductor structures such as quantum wells, quantum dots, quantum wires, quantum disks and superlattices. It is due to the enhanced confinement in lowdimensional semiconductor structures that many physical and chemical phenomena appear in these low-dimensional semiconductor structures. In these phenomena, the optical and electrical phenomena attract many attentions. By studying these phenomena we can produce the next-generation of device in the fields of defense industry, medical, remote sensing, communications and storage.In this paper, we mainly studied the nonlinear optical properties and hydrogenic impurity states in quantum wells and dots. Based on the effective-mass approximation,the wave function and energy eigenvalues can be obtained by solving Schrodinger equation.For nonlinear optical properties, the analytic expression of the third-harmonic generation coefficients, the optical absorption coefficients and refractive index changes are derived in detail by using the compact-density-matrix approach and iterative method, then the numerical results and some discussions are given. For the hydrogenic impurity states, we set a reasonable trial wave function after we got the wave function and energy eigenvalues,then we obtained the impurity binding energy by using the variational method. This paper mainly is divided into six chapters to write.In the first chapter, the development, the background, and the meaning of the lowdimensional nano materials are introduced, and the research method and contents are illustrated.In the second chapter, we discussed the influence of U₀ and d on the optical absorption coefficients by suing the model of the square tangent quantum dot. Based on the effective-mass approximation, we got the wave function and energy eigenvalues by solving Schr¨odinger equation of the system. The expression of the third-harmonic generation coefficients can be derived by using the compact-density-matrix approach and iterative method. The numerical results show that the peak value of the third-harmonic generation coefficients vary when U₀ and d change and the blue or red shift occur in the figure.In the third chapter, in order to illustrate the effect of impurity to the optical absorption coefficients and refractive index changes, we calculated the influence of the impurity in this chapter. In our calculation, we mainly used the variational method to solve the Schr¨odinger equation of the system, and got the expression of the optical absorption coefficients and refractive index changes by using the compact-density-matrix approach and iterative method. We found that the optical absorption coefficients and refractive index changes depend on the impurity, the impurity position, d and the incident photon energy.Consequently, we should take the impurity into consideration in the theoretical and experimental research. Besides, when the incident photon energy is large enough, the third order optical absorption coefficients and refractive index changes are unneglectable.In the fourth chapter, the hydrogenic impurity states in the symmetrically trigonometric potential quantum dot are investigated. By using the same method, based on the effective-mass approximation, we got the wave function and energy eigenvalues by solving Schr¨odinger equation of the system, then chose a reasonable trial wave function to calculate the impurity binding energy. The result shows that the impurity binding energy decreases when d and T increase. However, the impurity binding energy enhances with the increment of V₀ and P. Besides, the impurity binding energy increases when the impurity move to the center of the system, and have a maximum value when the impurity locates in the center of the system.In the fifth chapter, discusses of the impurity binding energy in detail are given. Here,we mainly calculated the effects of d, U₀, P and the impurity position on the impurity binding energy. After discussing and analyzing the results, we got that the impurity binding energy reduces as d increases or U₀ and P decrease. Moreover, the impurity position also plays an important role in the research of the impurity states.In the sixth chapter, the main conclusions and contents of the research are summarized. The shortage and the flowing work direction are pointed out.