Quasi-Ballistic Thermal Conduction in 6H-SiC

TL;DR

This study investigates quasi-ballistic thermal conduction in 6H-SiC, revealing how doping and porosity influence thermal transport at low temperatures, with implications for thermal management in electronic devices.

Contribution

It provides the first temperature-dependent measurements of thermal conductivity in doped and porous 6H-SiC, highlighting the effects of phonon scattering mechanisms and modeling thermal transport.

Findings

Strong quasi-ballistic thermal transport observed at low temperatures.

Dopants and boundaries significantly alter phonon scattering and thermal conductivity.

Boron dopants cause stronger phonon scattering than nitrogen dopants.

Abstract

The minimization of electronics makes heat dissipation of related devices an increasing challenge. When the size of materials is smaller than the phonon mean free paths, phonons transport without internal scatterings and laws of diffusive thermal conduction fail, resulting in significant reduction in the effective thermal conductivity. This work reports, for the first time, the temperature dependent thermal conductivity of doped epitaxial 6H-SiC and monocrystalline porous 6H-SiC below room temperature probed by time-domain thermoreflectance. Strong quasi-ballistic thermal transport was observed in these samples, especially at low temperatures. Doping and structural boundaries were applied to tune the quasi-ballistic thermal transport since dopants selectively scatter high-frequency phonons while boundaries scatter phonons with long mean free paths. Exceptionally strong phonon scattering by boron dopants are observed, compared to nitrogen dopants. Furthermore, orders of magnitude reduction in the measured thermal conductivity was observed at low temperatures for the porous 6H-SiC compared to the epitaxial 6H-SiC. Finally, first principles calculations and a simple Callaway model are built to understand the measured thermal conductivities. Our work sheds light on the fundamental understanding of thermal conduction in technologically-important wide bandgap semiconductors such as 6H-SiC and will impact applications such as thermal management of 6H-SiC-related electronics and devices.