Researches On Effect Of Guassian Distribution Phononic Cavities On Phonon Transport In The Semiconductor Nanowires

In recent years, the nanoscale structures and phonon devices have already become a focus of material science and the condensed matter physics due to their novel physical properties and potential applications. With the scale of the phonon devices decreasing,size effects on thermal conductance are of vital importance for device design.In this thesis,we have mainly investigated the influence of Gaussian distribution phononic cavities on phonon transmission and thermal conductance in the semiconductor nanowires. It is suggested that thermal conductance can be controlled by adjusting the geometry and structual parameters, which provides some theoretical basis for design and fabrication of some relevant quantum devices.We have studied the effects of Gaussian distribution phononic cavities and the length of region within phononic cavities on phonon transmission and thermal conductance in the semiconductor nanowire at low temperatures by using the scattering-matrix method. The results indicated that the more is Gaussian distribution phononic cavities embedded in the semiconductor nanowire, the more complex is the transmission spectra and the stronger is the mode splitting. In some cases, the stop-frequency gaps would appear. Moreover, the width and the number of frequency gaps would widen and increase with the number of the phononic cavities increasing, respectively. Meanwhile, due to the symmetry of Gaussian distribution, some abnormal phenomena appeared in thermal conductance. Thermal conductance spectra are overlap or crossing. These results show that we can control the phonon transmission and thermal conductance by inserting suitable number of phonon cavities or changing the parameters of structure. Our works can be used a reference for related nanodevice design.The acoustic phonon transport through a narrow semiconductor constriction which embedded Gaussian distribution phononic cavities is investigated by use of the scattering-matrix method. It is found that the phonon transmission is the selective resonant transmission with the number of the phononic cavities increasing, and the transmission spectra show a series of resonant peaks and dips. At low temperatures, the more is Gaussian phononic cavities inserted in the narrow constriction, the larger is the thermal conductance. Meanwhile, the total transmission coefficient reduces and the number of transmission peaks increases with the length of region within gaussian phononic cavities increasing. The symmetry of the Gaussian distribution leading to abnormal phenomena is present in thermal conductance, which shows that the phonon transmission and thermal conductance rely significantly on structure parameters. Therefore, we can control phonon transmission efficiency and thermal conductance by changing geometry shapes or controlling structure parameters to some extent.