$\text{A}{\text{l}}_x\text{G}{\text{a}}_{1-x}\text{N}/\text{GaN}$ superlattices are widely used in GaN-based power electronics and optoelectronics for regulation of electronic and optoelectronic properties. However, thermal transport in these superlattices, which is critical for device performance and reliability, remains poorly understood. In this work, we have systematically investigated the effect of alloy on thermal transport in $\text{A}{\text{l}}_x\text{G}{\text{a}}_{1-x}\text{N}/\text{GaN}$ superlattices using homogeneous nonequilibrium molecular dynamics based on machine-learning interatomic potentials. A nonmonotonic interface-density dependence of thermal conductivity κ is observed in both pristine AlN/GaN and $\text{A}{\text{l}}_x\text{G}{\text{a}}_{1-x}\text{N}/\text{GaN}$ superlattices, with a global minimum at an interface density of about $0.2\mathrm{n}{\mathrm{m}}^{-1}$. Unlike in AlN/GaN superlattices, the κ contributed by coherent phonons is largely suppressed in $\text{A}{\text{l}}_x\text{G}{\text{a}}_{1-x}\text{N}/\text{GaN}$ superlattices because alloy disorder disrupts the formation of coherent Bloch phonons by reducing interfacial modes and introducing scattering centers. As a result, the κ of $\text{A}{\text{l}}_x\text{G}{\text{a}}_{1-x}\text{N}/\text{GaN}$ superlattices at high interface densities approaches the values of the corresponding alloys with the same average composition, where thermal transport is dominated by incoherent phonons. This work provides deep insights into the strong effect of alloy on thermal transport in $\text{A}{\text{l}}_x\text{G}{\text{a}}_{1-x}\text{N}/\text{GaN}$ superlattices, and will benefit the regulation of thermal properties by superlattice design for applications in power electronics and optoelectronics.

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• Lattice dynamics
• Lattice thermal conductivity
• Phonons
• Thermal transport
• Alloys
• III-V semiconductors
• Superlattices
• First-principles calculations
• Machine learning
• Molecular dynamics