Journal of Materials Science

, Volume 55, Issue 4, pp 1592–1602 | Cite as

Thermally stable epitaxial ZrN/carrier-compensated Sc0.99Mg0.01N metal/semiconductor multilayers for thermionic energy conversion

  • Magnus GarbrechtEmail author
  • Ingrid McCarroll
  • Limei Yang
  • Vijay Bhatia
  • Bidesh Biswas
  • Dheemahi Rao
  • Julie M. Cairney
  • Bivas Saha
Electronic materials


Epitaxial metal/semiconductor multilayers are attractive materials for a range of solid-state energy conversion devices. Applications include waste-heat-to-electrical energy conversion, hot-electron-based solar energy conversion in photocatalysis and photodiodes, optical hyperbolic metamaterials, and engineering thermal hyperconductivity. ZrN/ScN is among the first metal/semiconductor multilayer structures to also display promising thermal and electronic properties. However, for efficient thermionic transport, it is necessary to control and tune the Schottky barrier height at the metal/semiconductor interfaces, since this controls current flows across the superlattices’ cross-plane directions. Sputter-deposited semiconducting ScN in ZrN/ScN multilayers contains a high concentration of n-type carriers, primarily due to oxygen impurities. This leads to a very small depletion width at metal/semiconductor interfaces, preventing thermionic transport. To overcome this challenge, the n-type carrier concentration of ScN has been reduced by Mg hole doping to ~ 1.6 × 1018 cm−3. In this article, we report the growth of thermally stable epitaxial ZrN/carrier-compensated Sc0.99Mg0.01N multilayers useful for thermionic emission-based devices. We present carrier concentration and transport regime calculations. Characterization of the microstructure and thermal stability was performed by combining aberration-corrected scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy mapping, and atom probe tomography. The results show stoichiometric Sc0.99Mg0.01N layers with a uniform magnesium concentration, and lattice-matched ZrN/Sc0.99Mg0.01N growth with smooth and atomically sharp interfaces that are thermally stable after 48 h at 950º C. The successful demonstration of thermally stable ZrN/carrier-compensated Sc0.99Mg0.01N multilayers with a semiconductor carrier concentration of 2 × 1018 cm−3 is expected to enable efficient thermionic transport devices with improved properties.



The authors acknowledge the facilities of the Microscopy Australia node at the University of Sydney (Sydney Microscopy & Microanalysis). BB, DR, and BS acknowledge financial assistance from the International Centre for Materials Science (ICMS) and Sheikh Saqr Laboratory (SSL) of Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR). The authors acknowledge Mr. Abhijeet Chatterjee for assistance with HRXRD measurements.

Author contributions

All authors contributed to this paper and have approved the final version of the manuscript. M.G. planned this study and carried out all TEM experiments, data analysis and plotting, and prepared figures. I. McC. carried out all APT experiments, data analysis and plotting, and figure preparation. L.Y. and V.B. prepared TEM and APT samples and read and commented on the manuscript. J.M.C. oversaw APT experiments, contributed to data interpretation, and commented on the manuscript. B.B. and D.R. carried out XRD characterization and transport regime calculations. B.S. conceptualized the research, performed sample growth, and read and commented on the manuscript.

Compliance with ethical standards

Conflict of interest

The authors declare no conflict of interest.


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© Springer Science+Business Media, LLC, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Australian Centre for Microscopy and MicroanalysisThe University of SydneyCamperdownAustralia
  2. 2.School of Aerospace, Mechanical and Mechatronic EngineeringThe University of SydneyCamperdownAustralia
  3. 3.Chemistry and Physics of Materials UnitJawaharlal Nehru Centre for Advanced Scientific ResearchBangaloreIndia
  4. 4.International Centre for Materials ScienceJawaharlal Nehru Centre for Advanced Scientific ResearchBangaloreIndia
  5. 5.School of Advanced Materials (SAMat)Jawaharlal Nehru Centre for Advanced Scientific ResearchBangaloreIndia

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