Investigation on thermal conductivity of graphene/gallium nitride heterostructure

Due to their excellent thermal, mechanical, optical, and electrical properties, graphene materials have attracted great attention. Gallium nitride is a more commonly used material in semiconductor devices. Therefore, the research of thermal conductivity of graphene / gallium nitride composite heterostructures has important application value. In this paper, the initial model structure of graphene / gallium nitride composite heterogeneous was built by material studio software. And then, the different sizes and thickness of graphene/gallium nitride composite heterostructures were constructed. The sizes of heterostructures are 27.50 Å, 41.25 Å, 68.75 Å, 82.51 Å and the thicknesses are 98.49 Å, 144.06 Å, 214.06 Å, 302.96 Å and 392.98 Å respectively. The thermal conductivity of heterostructures is calculated using molecular dynamics methods with system temperature as a variable between 100K~500K.The results show that when the width of the graphene / gallium nitride heterostructure remains the same, the thermal conductivity of the heterostructure increases as the length of the composite heterostructure increases. It is analyzed that as the length increases, the coupling effect of heterostructure grain boundary is enhanced. The change of phonon mean free path has an effect on heat conductivity coefficient of heterostructure. At the same time, the thermal conductivity of graphene / gallium nitride heterostructure gradually increases with system temperature increasing. We speculate that as the temperature increases, the scattering of inelastic phonons at the interface of the heterojunction increases, thereby promoting the phonon transmission of the model. Non-harmonic coupling effect is strengthened. When the thickness of gallium nitride increases, the thermal conductivity of composite heterostructures shows a non-linear increasing trend. It is explained that the mean free path of phonons in the z-direction of gallium nitride is larger than the size of the gallium nitride in the out-of-plane direction in the heterostructure. The findings will be beneficial to provide theoretical basis for thermal design of heterostructure for power devices.