Thermal energy transport model for macro-to-nanograin polycrystalline semiconductors

Abstract

Effective thermal conductivity of graphene-based composites Appl. Phys. Lett. 101, 121916 (2012) Assessment of phonon boundary scattering from light scattering standpoint J. Appl. Phys. 112, 063513 (2012) Visible photoluminescence in polycrystalline terbium doped aluminum nitride (Tb:AlN) ceramics with high thermal conductivity Appl. Phys. Lett. 101, 111903 (2012) Enhanced thermal conductivity of polycrystalline aluminum nitride thin films by optimizing the interface structure Understanding thermal energy transport in polycrystalline semiconductors is important for the efficiency of electronic devices and thermoelectric materials. In this paper, we study the reduction of the transport of thermal energy in polycrystalline semiconductors generated by the shortening of the phonon mean free paths due to grain boundary scattering. We calculate the reduction of the thermal conductivity in polycrystals, from macro-to-nanograin sizes and different temperatures, by using a theoretical approach based on the kinetic theory of transport processes. The approach involves an exact expression for the reduction of the phonon mean free paths that includes their directional, frequency, and polarization dependence. By comparing the results of our model for the reduced thermal conductivity of the grain against the thermal boundary Kapitza resistance calculated by others, we find that the thermal conductivity of polycrystalline Si and SiC materials is dominated by the reduced thermal conductivity of the grain. We also show that in order to accurately calculate the thermal conductivity, the proportion of heat transported by transverse and longitudinal phonons must be correctly taken into account. By using the model, we study grain boundary scattering effects on the reduction of the thermal conductivity of polycrystalline silicon and silicon carbide. The calculated results are compared with experiments at different temperatures and grain sizes without using free adjustable variables (e.g., defects concentration) or phenomenological formulas to account for the reduced thermal conductivity of the grain.

Relative importance of grain boundaries and size effects in thermal conductivity of nanocrystalline materials

“…1), a good agreement between them has been observed, demonstrating that our newly developed model for ETC is effective for nanocrystalline materials. In addition, a good agreement between our model and experimental ETC141518 for nanocrystalline silicon at 300  K (refer to Supplementary discussion 4 and Fig. S7) has also been observed, which further confirmed that our model is valid.…”

“…(3) better amenable to practical application, a simple theoretical ECT model for nanocrystalline materials has been proposed in this work by considering both single crystal thermal properties and the Kaptiza thermal resistance. By comparing our theoretical predictions with simulated results for the ECT of nanocrystalline diamond at 300  K as well as experimental ETC of nanocrystalline silicon141518 at 300  K , a good agreement between them has been obtained, which proves the rationality behind our ECT formula. Although the effect of both GBs and size effects can be expressed by using the grain size in this ECT formula, the mechanisms of action in these two factors on ETC are totally different151920, and further the contribution of these two factors on ETC may be different for different materials and grain sizes.…”

Porous Nano-SiC as Thermal Insulator: Wisdom on Balancing Thermal Stability, High Strength and Low Thermal Conductivity

“…We refer to the method of Maldovan's model. [31] This model calculated the thermal conductivity for bulk polycrystalline SiC by considering intrinsic Umkplapp phonon scattering, phonon-grain boundary scattering, and thermal boundary Kapitza conductance. The present grain size d inputted in Maldovan's model was determined by counting at least 100 grains in corresponding TEM images of each sample.…”

Grid-supported EUV pellicles: A theoretical investigation for added value

“…The thermal conductivity, , ranges in the literature from 0.2 up to 34 W/m/K 9 . The different material properties are a function of temperature, the crystal grains size and the film thickness 10 . To determine the sensitivity of the pellicle behavior, the thermal conductivity has been varied over the full range.…”