Origin of the Strong Anharmonic-induced Abnormal Thermal Conductivity in Semiconductors

Abstract Semiconducting materials are the foundations of electronics and optoelectronics, and their heat management guides the design of highly efficient devices. For most semiconductors, the thermal conductivity of materials composed of light chemical species is higher than that of the iso-structured materials with heavy elements. For example, bulk Si shows a thermal conductivity higher than Ge. However, for many copper-based compounds, e.g., Cu halides, the thermal conductivity increases monotonously as the atomic number of halogens increases. On the other hand, for lead chalcogenides, the thermal conductivity of PbSe is lower than PbS and PbTe. In this work, we reveal that the combined effect of electronic states coupling and phonon collisions, giving rise to strong anharmonicity, is responsible for the abnormal trend of thermal conductivity of Cu halides and Pb chalcogenides. From CuCl to CuBr and CuI, the increasing thermal conductivity is due to the decreasing electronic coupling strength between Cu-occupied 3d and unoccupied 4s states when crystal symmetry is reduced, which leads to the increase of atomic vibrational potential energy and reduction of lattice anharmonicity. In Pb chalcogenides, the unusually lower thermal conductivity of PbSe than PbTe and PbS is mainly due to the intensive scattering between phonons caused by the localized transverse acoustic modes and soft optical modes, which outweigh the contribution of the crystal anharmonicity due to the anharmonic potential energy surface.