Search

Calculations are presented in this paper for the flow fields, growth rate and solute transport during crystal growth from solution at various gravity levels.

The calculations of the ground and a few low-lying excited states of impurity in the quantum wells (QW's) are presented by making use of a functional variational approach. A new trial wave function is proposed. It is taken by the product of the exact subband state in the QW and the state of two-dimensional hydrogenic-like donor with an effective charge distribution along the -direction (perpendicular to the well interfaces). The variation of binding energies of the donor states in the QW with the well-width is calculated. The calculated result is compared with that obtained by the earlier variational method. The functional variational approach proposed here has some benefits such as, to bring a great flexibility and to apply to a relatively large species of trial wave functions.

We present for the first time completely analytical variational expressions for the calculations of the binding energies of the low-lying bound states of a hydrogenic donor in a quantum well (QW). To demonstrate the use of these expressions we have theoretically studied the binding energies for the ground state and a few low-lying excited states of a hydrogenic donor in a stepped quantum well (SQW). The numerical results show that the binding-energy curves in the SQW exhibit a non-symmetrical structure relative to the center of the QW and depend on the height of the sub-barrier. The maximum in the binding energies increases with increasing step potential. These effects can be interpreted by referring to the variation of the electron probability-density distribution of the lowest subband in the SQW.

A fluctuation model is presented for a mode-locked laser incorporating a mirror with intensity dependent reflection coefficient. Computer simulation with this model is executed for some nonlinear crystals and for varied parameters. The optimum parameters and conditions under which good mode-locking will be achieved is predicted according to the simulation calculation.

The effect of various islandlike obstacles, placed inside an electron waveguide, and the disordered tunneling modulation on the quantized conductance is theoretically investigated with use of a model of two coupled chains. The Landauer-B\"uttiker prescription, the tight-binding approximation, and the transfer-matrix method are used to calculate the conductance of this mesoscopic system. The islandlike obstacles with different shapes are described by different regular tunneling modulations in a finite active region. Both the propagating and evanescent modes in all the regions are taken into account in our calculations. The calculated results show that for these structures there are basic plateau structures in the conductance curve as a function of the Fermi energy. In addition, resonance structures are superimposed on the plateaus. However, the accuracy of the quantization and the resonance pattern in the conductance strongly depend on the interchannel tunneling modulations. The resonance structures in the conductance plateaus are smeared when the corresponding tunneling modulation alters smoothly over the obstacle region. We also study the variation of the quantized conductance with the Fermi energy for various multiply connected structures and for a system containing a finite-length obstacle with periodically modulated tunneling. A series of features in the conductance curve emerge. Roughness or corrugation always exists on the surfaces of the obstacles. This effect can be characterized by the randomly modulated tunneling between the two channels.In this work we also present the investigation of the influence of the tunneling disorder on the conductance. The effects of disordered interchain tunneling are threefold. First, it rounds the sharp corners of the quantization conductance. Second, it produces conductance fluctuations imposed on the plateaus. And third, the average value of the conductance is reduced by the interchain tunneling disorder. Both the localization length and the root-mean-square value of conductance fluctuations depend on the extent of disorder and the Fermi energy. We also present the statistical distribution of conductance fluctuations in this disordering system. It is found that the statistical distribution can be normal, log-normal, or neither the former nor the latter, depending on the extent of disorder and the Fermi energy. Finally, we have studied the combined effect of both the site-energy disorder and the tunneling disorder on the conductance. We find that the two disorders are of a very similar nature. In summary, we conclude that this two-coupled-chain model is shown to describe the essence of quantum ballistic transport of electrons in a nonuniform electron waveguide with two channels in a simple and transparent way.

The effect of different tunneling modulations on the quantized conductance in a coupled double electron waveguide is theoretically investigated with the use of a model of two coupled chains. The calculated results show that both the accuracy of the quantization in the conductance and the resonance pattern strongly depend on the tunneling modulation between two channels. The resonance structures in the conductance plateaus are smeared when the corresponding tunneling modulation alters smoothly over the obstacle region. We also study the variation of the quantized conductance with the Fermi energy for various doubly-connected structures. A series of new novel features in the conductance curve emerge. We find that this two coupled chain model is shown to describe the essence of quantum ballistic transport of electrons in the two coupled electron waveguide in a simple and transparent way.