Phonon focusing effect on thermal conductivity of hexagonal group III-nitrides and silicon carbide crystals

• Published in: Physics letters. A 2020-02, Vol.384 (5), p.126120, Article 126120
• Main Authors: Chernodoubov, D.A., Inyushkin, A.V.
• Format: Article
• Language: English
• Subjects: Phonon focusing; Thermal conductivity; Wide-band-gap semiconductors
• ISSN: 0375-9601; 1873-2429
• DOI: 10.1016/j.physleta.2019.126120

•Thermal conductivity of hexagonal wide-band-gap semiconductors is calculated accounting the effect of phonon focusing.•T2 mode contributes the most to arising anisotropy.•Phonon focusing decreases thermal conductivity in the c axis direction and perpendicular to it and increases it in 45 degrees.•Phonon focusing does not change thermal conductivity value in the direction of 60 degrees to the c axis in hexagonal crystals.•The orientation of rectangular cross-section sample sides can significantly change the value of thermal conductivity. Thermal conductivity κ of 4H-, 6H-SiC and wurtzite GaN, InN, AlN crystals is calculated accounting phonon focusing effect at low temperatures with only diffusive phonon boundary scattering. The orientation dependence of thermal conductivity is similar in these materials. Thermal conductivity is enhanced in the direction of approximately 45∘ to the c axis up to 27% for GaN, 24% for 6H-SiC, 32% for InN, and 9% for AlN compared to the isotropic case for the circular cross-section and finite-length samples. Contributions of transverse T1 and T2 modes are nearly the same, about 40–45%, while the focusing of T2 mode contributes essentially to the angular dependence of κ. We find that the phonon focusing does not change κ value (within 5%) in the direction of 60∘ to the c axis in all hexagonal crystals studied so far.