Metal/Semiconductor Superlattices: Promise for a New Paradigm in Solid-State Energy Conversion

Ever since the theoretical proposal of Esaki and Tsu on the band-structure engineering of materials by employing artificially structured superlattices, semiconductor based superlattice metamaterials have impacted the world in many profound ways. Semiconductor based superlattices such as GaAs/AlAs and others have resulted in many novel physics based concepts, and are actively researched and developed for many industrial applications. In contrast to the semiconductor/ semiconductor superlattices, development of epitaxial, single crystalline metal/semiconductor superlattices have eluded researchers for several decades primarily due to the extraordinarily difficult growth and material compatibility challenges. We have developed the first epitaxial, single crystalline metal/semiconductor superlattices based on TiN/(Al,Sc)N material system that are free from extended defects. These lattice-matched rocksalt nitride metamaterials 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. 

In this presentation, we will describe the growth, characterization, and transport properties of nitride metal/semiconductor superlattice and multilayers including (Ti,W)N/(Al,Sc)N and (Hf, Zr)N/ScN. Potential applications of these superlattices in thermoelectric and thermionic energy conversion devices, plasmonic and hyperbolic metamaterials, and hot-electron based solar energy conversion devices will be discussed. Furthermore, we will demonstrate how these novel metamaterials serve as perfect model systems for investigating fundamentals of heat and current transport in nanostructured materials.