title: Anisotropic temperature-dependent thermal conductivity by an Al2O3interlayer in Al2O3/ZnO superlattice films.
abstract: The thermal conductivity of superlattice films is generally anisotropic and should be studied separately in the in-plane and cross-plane directions of the films. However, previous works have mostly focused on the cross-plane thermal conductivity because the electrons and phonons in the cross-plane direction of superlattice films may result in much stronger interface scattering than that in the in-plane direction. Nevertheless, it is highly desirable to perform systematic studies on the effect of interface formation in semiconducting superlattice films on both in-plane and cross-plane thermal conductivities. In this study, we determine both the in-plane and cross-plane thermal conductivities of Al2O3(AO)/ZnO superlattice films grown by atomic layer deposition (ALD) on SiO2/Si substrates in the temperature range of 50-300 K by the four-point-probe 3-ω method. Our experimental results indicate that the formation of an atomic AO layer (0.82 nm) significantly contributes to the decrease of the cross-plane thermal conductivity of the AO/ZnO superlattice films compared with that of AO/ZnO thin films. The cross-plane thermal conductivity (0.26-0.63 W m-1K-1of the AO/ZnO superlattice films (with an AO layer of ∼0.82 nm thickness) is approximately ∼150%-370% less than the in-plane thermal conductivity (0.96-1.19 W m-1K-1) of the corresponding film, implying significant anisotropy. This indicates that the suppression of the cross-plane thermal conductivity is mainly attributed to the superlattice, rather than the nanograin columnar structure in the films. In addition, we theoretically analyzed strong anisotropic behavior of the in-plane and cross-plane thermal conductivities of the AO/ZnO superlattice films in terms of temperature dependence.
authors.affiliation: Department of Physics, Chung-Ang University, Seoul 156-756, Republic of Korea.
authors.forename: Won-Yong
authors.initials: WY
authors.lastname: Lee
authors.forename: Jung-Hoon
authors.initials: JH
authors.lastname: Lee
authors.forename: Jae-Young
authors.initials: JY
authors.lastname: Ahn
authors.forename: Tae-Hyun
authors.initials: TH
authors.lastname: Park
authors.forename: No-Won
authors.initials: NW
authors.lastname: Park
authors.forename: Gil-Sung
authors.initials: GS
authors.lastname: Kim
authors.forename: Jin-Seong
authors.initials: JS
authors.lastname: Park
authors.forename: Sang-Kwon
authors.initials: SK
authors.lastname: Lee