Study On The Effect Of Contact Shapes On Ballistic Phonon Transport In Semiconductor Nanowires

Feynman’s prediction for nanotechnology, the development of superlattice and successful preparation of Fe nanoparticle, making nanotechnology become one of the frontier research topics in Physics and materials science. Meanwhile, the rapid development of nanoscience and nanotechnology takes the characteristic dimension of photoelectric device into nanometer level, the size effect and explosively growth of high density heat transport are the critical problem to affect and restrict the performance and stability of devices. Therefore, study on nanoscale heat transport has been receiving great attentions. In this article, by using scattering matrix method, transport and thermal conductance of ballistic phonon in the semiconductor nanowires are discussed, some interesting phenomenon is revealed.Ballistic phonon transport and thermal conductance in semiconductor nanowires linked by two incontinuity contacts are studied by use of elastic scalar model and scattering matrix method. It is discovered that the transmission coefficients in semiconductor nanowires linked by abrupt contact display irregularly and appear sharp dips. While the semiconductor nanowires linked by steplike contact, whose transmission coefficient curves exhibit regular quantized platforms, moreover, transmission jumps will arise at some reduced frequencies. When the temperature tends to zero and the structure becomes a strait channel the total thermal conductance closes to the quantum unit of thermal conductance. The thermal conductance increases linearly with increasing temperature at higher temperature. In addition, the existence of the steplike contact makes the thermal conductance higher.By way of the scattering matrix method, the effect on the ballistic phonon transmission and thermal conductance of three continuity contacts in semiconductor nanowires are investigated. It is found that the contact shapes can dramatically affect the transmission spectra when the transverse widths of left and right nanowires are fixed. The transmission coefficient is the biggest in the catenoidal contact as the reduced frequency tends to zero. At lower reduced frequencies, the transmission coefficients increase with the increasing reduced frequencies, and the smallest one is in the catenoidal contact. As the frequency is higher, there is no evident regularity of the variation of transmission coefficient in three continuity contacts. The shape-dependent of phonon transmission can be ascribed to different phonon couplings in the contacts. The trapezium type contact has the largest thermal conductance at lower temperature, while the catenoidal contact is the smallest one. As the temperature increases, the largest thermal conductance appears in the semiconductor nanowire with trapezium type contact. Comparing with incontinuity contacts can obtain that the semiconductor nanowires linked by continuity contacts has larger transmission coefficients and thermal conductance than the incontinuity contacts. These results indicate that choosing an appropriate contact shape can enhance the acoustic phonon thermal conductance.