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    Cross-plane thermal conductivity of (Ti,W)N/(Al,Sc)N metal/semiconductor superlattices

    Bivas Saha1,4,†, Yee Rui Koh2,4,†, Jonathan Comparan1,4, Sridhar Sadasivam3,4, Jeremy L. Schroeder5, Magnus Garbrecht5, Amr Mohammed2,4, Jens Birch5, Timothy Fisher3,4 et al.

    Ali Shakouri2,4 and Timothy D. Sands6

    • 1School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, USA
    • 2School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
    • 3School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907, USA
    • 4Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
    • 5Thin Film Physics Division, Department of Physics, Chemistry, and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden
    • 6Bradley Department of Electrical and Computer Engineering and Department of Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia 24061, USA

    • *Present address: Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, CA 94720, USA; bsaha@berkeley.edu
    • †These authors have contributed equally in this work.
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    Phys. Rev. B 93, 045311 – Published 21 January, 2016

    DOI: https://doi.org/10.1103/PhysRevB.93.045311

    Abstract

    Reduction of cross-plane thermal conductivity and understanding of the mechanisms of heat transport in nanostructured metal/semiconductor superlattices are crucial for their potential applications in thermoelectric and thermionic energy conversion devices, thermal management systems, and thermal barrier coatings. We have developed epitaxial (Ti,W)N/(Al,Sc)N metal/semiconductor superlattices with periodicity ranging from 1 nm to 240 nm that show significantly lower thermal conductivity compared to the parent TiN/(Al,Sc)N superlattice system. The (Ti,W)N/(Al,Sc)N superlattices grow with [001] orientation on the MgO(001) substrates with well-defined coherent layers and are nominally single crystalline with low densities of extended defects. Cross-plane thermal conductivity (measured by time-domain thermoreflectance) decreases with an increase in the superlattice interface density in a manner that is consistent with incoherent phonon boundary scattering. Thermal conductivity values saturate at 1.7Wm−1K−1 for short superlattice periods possibly due to a delicate balance between long-wavelength coherent phonon modes and incoherent phonon scattering from heavy tungsten atomic sites and superlattice interfaces. First-principles density functional perturbation theory based calculations are performed to model the vibrational spectrum of the individual component materials, and transport models are used to explain the interface thermal conductance across the (Ti,W)N/(Al,Sc)N interfaces as a function of periodicity. The long-wavelength coherent phonon modes are expected to play a dominant role in the thermal transport properties of the short-period superlattices. Our analysis of the thermal transport properties of (Ti,W)N/(Al,Sc)N metal/semiconductor superlattices addresses fundamental questions about heat transport in multilayer materials.

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    Phys. Rev. B 93, 045311– Published 21 January, 2016
    • Received 26 February 2015
    • Revised 10 September 2015

    ©2016 American Physical Society

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