Effects of surface charges on phonon properties and thermal conductivity in GaN nanofilms*

Abstract

Surface charges can modify the elastic modulus of nanostructure, leading to the change of the phonon and thermal properties in semiconductor nanostructure. In this work, the influence of surface charges on the phonon properties and phonon thermal conductivity of GaN nanofilm are quantitatively investigated. In the framework of continuum mechanics, the modified elastic modulus can be derived for the nanofilm with surface charges. The elastic model is presented to analyze the phonon properties such as the phonon dispersion relation, phonon group velocity, density of states of phonons in nanofilm with the surface charges. The phonon thermal conductivity of nanofilm can be obtained by considering surface charges. The simulation results demonstrate that surface charges can significantly change the phonon properties and thermal conductivity in a GaN nanofilm. Positive surface charges reduce the phonon energy and phonon group velocity but increase the density of states of phonons. The surface charges can change the size and temperature dependence of phonon thermal conductivity of GaN nanofilm. Based on these theoretical results, one can adjust the phonon properties and temperature/size dependent thermal conductivity in GaN nanofilm by changing the surface charges.

First-principles analysis of phonon thermal transport properties of two-dimensional WS2/WSe2 heterostructures*

“…As mentioned above, the atomic vibrations perpendicular to the xy plane are affected by the vdW interaction. For the modification on the elastic modulus of nanostructure resulted from the interface charges, [67] the interface effects usually play a significant role in exploring phonon and thermal transport properties of the vdW heterostructures. Therefore, the distribution of charge density difference of the WS 2 /WSe 2 -BHs and the charge redistribution and transfer among the single-layer WS 2 and WSe 2 surfaces can be gained as shown in Fig.…”

Enhancement of thermal rectification by asymmetry engineering of thermal conductivity and geometric structure for multi-segment thermal rectifier

“…Most models proposed in this work can be realized in experiments in both the macroscopic scale and the microscopic scale, as long as the Fourier law is still valid within the scale of size. With progress of thermal conductivity in materials in multi-scale [46,[74][75][76][77][78][79][80][81][82] or thin films [83,84] or bulk form, [83][84][85][86] the design of efficient thermal rectifiers will have more choices of components. Many advances of characterization [87,88] will be helpful to reveal the microstructures and properties (such as phonon scattering, thermal conductivity, thermal diffusion, thermal capacity, etc.…”

Cross-plane thermal conductivity of GaN/AlN superlattices

“…A decrease of the bulk thermal conductivity of III-nitrides due to impurity doping [26][27][28][29] was also found, while an enhanced conductivity is reported for isotopically enriched GaN 30 . For AlN/GaN stacks, significant changes in the phonon properties due to interface effects [31][32][33][34] and strain 35 were reported, while for compositionally graded interfaces it was found that alloy scattering is dominant over mismatch scattering 36 of phonons.…”