β-Ga₂O₃ is a promising ultrawide-bandgap semiconductor for high-voltage and high-power electronic devices owing to its large bandgap and high breakdown electric field. However, its relatively low thermal conductivity can lead to severe self-heating under high-power operating conditions. Integrating β-Ga₂O₃ with Si offers a feasible route for combining its superior electronic properties with mature Si-based processing technologies, whereas the interfacial thermal resistance may significantly impede heat dissipation across the β-Ga₂O₃/Si heterointerface. Because β-Ga₂O₃ has a monoclinic crystal structure and strongly anisotropic phonon transport properties, its crystal orientation may substantially affect interfacial phonon transmission. Clarifying the orientation-dependent thermal transport across β-Ga₂O₃/Si heterointerfaces is therefore important for interfacial thermal management and crystal-orientation selection.
In this work, β-Ga₂O₃/Si heterointerface models with (100), (010), and (001) β-Ga₂O₃ surfaces were constructed, and their interfacial thermal conductance was calculated using nonequilibrium molecular dynamics simulations. The phonon density of states, phonon transmission function, spectral thermal conductance, and accumulated spectral thermal conductance were further analyzed to elucidate the microscopic phonon transport mechanisms. The results show that the interfacial thermal conductance strongly depends on the crystal orientation of β-Ga₂O₃. At 300 K, the (010) interface exhibits the highest interfacial thermal conductance of approximately 288 MW·m^-2·K^-1, followed by the (001) and (100) interfaces with values of approximately 242 and 122 MW·m^-2·K^-1, respectively.
Phonon spectral analysis indicates that the orientation dependence of the interfacial thermal conductance mainly originates from differences in phonon spectral matching and low- to mid-frequency phonon transmission across the interface. Phonons below 20 THz dominate the interfacial thermal transport, with phonons below 10 THz providing the major contribution. The (010) interface exhibits higher phonon transmission and spectral thermal conductance within the dominant frequency range, whereas phonon transmission across the (100) interface is significantly suppressed. Increasing temperature generally enhances the interfacial thermal conductance, while the relative ordering among the three crystal orientations remains nearly unchanged. For the (001) interface, the slight decrease in interfacial thermal conductance from 500 to 600 K may arise from competition between the activation of additional phonon modes and enhanced phonon-phonon scattering. These results demonstrate that crystal orientation plays an important role in regulating thermal transport across β-Ga₂O₃/Si heterointerfaces and provide theoretical guidance for the thermal management of β-Ga₂O₃/Si heterointegrated devices.