Metal/Semiconductor Superlattices: A New Class of Artificially Structured Materials

Artificially structured materials in the form of superlattice heterostructures enable the search for exotic new physics, novel device functionalities, and serve as tools to push the fundamentals of scientific and engineering knowledge. Semiconductor heterostructures are the most celebrated and widely studied artificially structured materials, having led to the development of quantum well lasers, quantum cascade lasers, measurements of the fractional quantum hall effect and numerous other scientific concepts and practical device technologies. However, combining metals with semiconductors at the atomic scale to develop metal/semiconductor superlattices and heterostructures has remained a profoundly difficult scientific and engineering challenge. Though the potential applications of metal/semiconductor heterostructures could range from energy conversion to photonic computing to high-temperature electronics, materials challenges primarily had severely limited progress in this pursuit until very recently.

We developed the first epitaxial metal/semiconductor multilayer and superlattices that are free of extended defects. These rocksalt nitride superlattices have atomically sharp interfaces and properties that are tunable by alloying, doping and quantum size effects. Furthermore, these nitride superlattices exhibit exceptional mechanical hardness, chemical stability and thermal stability up to ~1000 ֩ C.

Our current research effort is directed towards the development of this novel research field with furthering the material details, and development of tunable Schottky barrier heights from few meV. to several eV.

Publication

1. B. Saha, A. Shakouri and T. D. Sands, "Rocksalt Nitride Metal/Semiconductor Superlattices: A New Class of Artificially-Structured Materials". Appl. Phys. Rev. 5, 021101 (2018) Editors Pick, Feature Article and Most Downloaded Paper.

2. M. Garbrecht, L. Hultman, M. H. Fawey, T. D. Sands, and B. Saha, "Tailoring of plasmon resonances in TiN/(Al,Sc)N superlattices by interlayer thickness variation", J. Mater. Sci. 53, 4001 (2018).

3. 21. M. Garbrecht, L. Hultman, T. D. Sands, and B. Saha. "Void-mediated coherency-strain relaxation and impediment of cubic-to-hexagonal transformation in epitaxial metastable metal/semiconductor TiN/Al0.72Sc0.28N multilayers" Phys. Rev. Materials 1, 033402, (2017).

4. M. Garbrecht, B. Saha, J. L. Schroeder, L. Hultman, and T. D. Sands, "Dislocation Pipe Diffusion in Nitride Superlattices Directly Observed in Lattice Resolved Microscopy." Sci. Rep. 7, 46092 (2017).

5. M. Garbrecht, J. L. Schroeder, L. Hultman, J. Birch, B. Saha and T. D. Sands, "Microstructural evolution and thermal stability of ZrxHf1-xN/ScN (x= 0, 0.5, 1) metal/semiconductor superlattices", J. Mater. Sci., 51, 8250 (2016).

6. J. L. Schroeder, B. Saha, M. Garbrecht, N. Schell, T. D. Sands, and J. Birch, "Thermal stability of epitaxial TiN/(Al,Sc)N metal/semiconductor superlattices for refractory applications." J. Mater. Sci. 50 (8), 3200-3206 (2015).

7. B. Saha, S. K. Lawrence, J. L. Schroeder, J. Birch, D. F. Bahr, and T. D. Sands, "Enhanced Hardness in Epitaxial TiAlScN Alloy Thin Films and Rocksalt TiN/(Al,Sc)N Superlattices." Appl. Phys. Lett. 105, 151904 (2014).

8. B. Saha, T. D. Sands and U. V. Waghmare, "Electronic structure, vibrational spectra and thermal properties of HfN/ScN metal/semiconductor superlattices: A first-principles Study." J. Phys.: Cond. Matt., 24 415303, (2012).

9. B. Saha, T. D. Sands and U. V. Waghmare, "First-principles analysis of thermoelectric ZrN/ScN metal/semiconductor superlattices", J. Appl. Phys. 109, 073720 (2011).