Non-equilibrium Thermal Resistance of Interfaces Between III-V Compounds

Abstract: Interfacial thermal resistance has been often estimated and understood using the Landauer formalism that assumes incident phonons with equilibrium distribution. However, previous studies suggest that phonons are out-of-equilibrium near the interface because of the heat flow through the leads and the scattering of phonons by the interface. In this paper, we report a systematic study on how vibrational spectra mismatch affects the degree of phonon non-equilibrium near an interface, how fast it is relaxed as the phonons diffuse into a lead, and the overall interfacial thermal resistance from the non-equilibrium phonons. Our discussion is based on the solution of the Peierls-Boltzmann transport equation with ab initio inputs for 36 interfaces between semi-infinite group-III (Al, Ga, In) and group-V (P, As, Sb) compound semiconductor leads. The simulation reveals that the non-equilibrium phonons cause significant interfacial thermal resistance for all 36 interfaces, making the overall interfacial thermal resistance two to three times larger than that predicted by the Landauer formalism. We observe a clear trend that the degree of phonon non-equilibrium near an interface and the interfacial thermal resistance from the non-equilibrium phonons increase as the mismatch of the Debye temperature of two lead materials increases. This contrasts with Landauer formalism's predictions, which show no correlation with the Debye temperature mismatch. The relaxation length of the phonon non-equilibrium varies significantly from 50nm to 1.5um depending on the combination of the lead materials. The relaxation length is proportional to the phonon mean free path of the corresponding lead material but also largely depends on the material in the opposite lead. This suggests the relaxation length cannot be considered an intrinsic property of the corresponding lead material.