Interface-independent sound speed and thermal conductivity of atomic- layer-deposition-grown amorphous AlN/Al₂O₃ multilayers with varying oxygen composition

MSB Hoque and IA Brummel and ER Hoglund and CJ Dionne and K Aryana and JA Tomko and JT Gaskins and D Hirt and SW Smith and T Beechem and JM Howe and A Giri and JF Ihlefeld and PE Hopkins, PHYSICAL REVIEW MATERIALS, 7, 025401 (2023).

DOI: 10.1103/PhysRevMaterials.7.025401

Dielectric amorphous multilayers (AMLs) play a critical role in a wide array of technologies such as optical coatings, nanoelectronics, energy harvesting, and recovery devices. However, despite their wide applications, a robust understanding of the effect of the interplay between chemical and structural disorder on the thermal properties of AMLs is still lacking. Therefore, in this paper, we experimentally and numerically investigate the effects of composition and interface density on the sound speed and thermal conductivity of a series of amorphous aluminum nitride and aluminum oxide multilayers grown via plasma- enhanced atomic layer deposition. To systematically change the composition, the oxygen content of the AMLs is proportionally varied with interface density during growth. We find that the longitudinal sound speed of these AMLs is dictated by the oxygen content instead of the number of interfaces. The thermal conductivity, in contrast, is dictated by both interface density and oxygen content. The interfaces act to decrease the thermal conductivity, whereas the oxygen content increases the thermal conductivity. Due to the competing influence of the interfaces and oxygen content, the thermal conductivity of the AMLs remains nearly constant as a function of interface density. Our study provides crucial insights into the effect of the interplay of composition and interfaces on the sound speed and thermal conductivity of AMLs.

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