Research On Transmission Characteristics Of Electrons And Phonons In Nano Devices

Nano materials are extensively used because of their small dimensions, as a result of which, quantum size effect appears in materials. In quantum dots and quantum trap, when sample dimentions are compareble to excition radius, in materials many discrete nenergy levels appear. When electrons or phonons are moving in nano materials, the obvious quantum size effect could be observed. In nearly several years, with the fast advance of nano science and technology and the micromation of designing various semiconductor devices, the interests and values of studying quantum size effect are increasing.To investigate the elastic transmiting characteristics of electrons or phonons in nano materials, there are many methods, such as Quantum scattering-matrix method, Green's function method, Finite-element method and so on. Quantum scattering-matrix method is to get reflection coefficients and transmission coefficients using the wave functions of electrons or phonons and the boundary-match conditions, so that we could calculate the electron conductance and the phonon thermal conductance. This method is easy to use and could give us a exacter result, but this method could not be used when big devices or irregular modes are studyed. Green's function method is to discretize the system into slices and assumes that only nearest-neighbor slices are coupled to one another. Though the assumption works fine for a closed system, the applicability of this method to devices is very finite. Finite-element method can be used in various devices, but it is so complex for many researchers to use it. In present several decades, many scientists have detailedly studyed the transmission characteristics of electrons in nano materials including magnetic field or not. Theoretically only a few studys have been done about the transmission features of phonons in nano materials.In this paper, with the help of Quantum scattering-matrix method, we detailedly investigated the elastic transmit characters of electrons and phonons in nano materials, including electrons transmission features in two-terminal structure containing an impurity and phonons transmission features in four-terminal structure. By theoretical deduce and numerical calculation, we find: (1)The repulsive impurity and attractive impurity both depress the conductance when they are sited in the narrow wire; (2)The resonant and anti-resonant structures are visible on the conductance plateaus; (3) The transmission coefficient and thermal conductance for each region are highly sensitive to geometric parameters, but the total thermal conductance for all regions holds the same value when the value of b/a is changing; and (4) At low temperature, the reduced thermal conductance for all terminals is dominated by the lowest mode, when the temperature increases, higher modes are excited and begin to play a role, the total thermal conductance increases.