Thermal stability of epitaxial cubic-TiN/(Al,Sc)N metal/semiconductor superlattices

Abstract

We report on the thermal stability of epitaxial cubic-TiN/(Al,Sc)N metal/semiconductor superlattices for potential plasmonic, thermoelectric, and hard coating applications.TiN/Al 0.72 Sc 0.28 N superlattices were annealed at 950 °C and 1050 °C for 4, 24, and 120 hours, and the thermal stability was characterized by high-energy synchrotron-radiation based 2D x-ray diffraction, high-resolution (scanning) transmission electron microscopy (HR(S)/TEM), and energy dispersive x-ray spectroscopy (EDX) mapping. The TiN/Al 0.72 Sc 0.28 N superlattices were nominally stable for up to 4 hours at both 950 °C and 1050 °C. Further annealing treatments for 24 hours and 120 hours at 950 °C led to severe interdiffusion between the layers and the metastable cubic-Al 0.72 Sc 0.28 N layers partially transformed into cubic-Al 0.72-x Sc 0.28 N and thermodynamically stable hexagonal-AlN phases with the h-AlN grains displaying two epitaxial variants with respect to c-TiN and c-Al 0.72-x Sc 0.28 N. EDX mapping suggests that scandium has a higher tendency for diffusion in TiN/(Al,Sc)N than titanium or aluminum. Our results indicate that the kinetics of interdiffusion and the cubic to hexagonal phase transformation play a major role when designing TiN/(Al,Sc)N superlattices for high temperature applications.

Microstructural evolution and thermal stability of HfN/ScN, ZrN/ScN, and Hf0.5Zr0.5N/ScN metal/semiconductor superlattices

“…As mentioned above, prior annealing studies on metal/semiconductor superlattices that employed TiN as the metallic compound showed thermal instability by interdiffusion between the layers, which eventually led to a loss of the global superlattice structure [12]. As for the Zr-and Hf-based material systems discussed here, all three superlattice systems were thermally stable (i.e., no detectable diffusion of metal atoms in between the layers) under the exactly same annealing conditions that were used in the TiN(Al,Sc)N study (Figs.…”

“…The microscopic study also demonstrated that a significant amount of metal atom diffusion between the metal and semiconductor layers occurs after annealing the superlattices to 950°C for more than 24 h [12]. Since working temperatures of up to 1000°C are common for applications in both high-temperature thermoelectric materials [13,14] and hard coatings of cutting tools [15,16], maintaining long-time thermal stability under such working conditions is crucial for any candidate system.…”

“…High-resolution EDX mapping in aberration-corrected STEM mode highlights significantly improved thermal stability of the (Hf,Zr)N/ScN-based superlattices compared to previous thermal stability studies on TiN/ScN-based superlattices [12]. Moreover, interface quality, phase purity, film morphology and microstructure, and evolution under annealing were investigated by atomically resolved S/TEM analysis.…”

“…Combining aberration-corrected high-resolution (HR) S/TEM imaging and EDX mapping proved to be an optimal tool for the investigation of the thermal stability of the superlattices as well as phase purity, quality of interfaces, and film morphology [9,12].…”

Tailoring of surface plasmon resonances in TiN/(Al0.72Sc0.28)N multilayers by dielectric layer thickness variation

“…Moreover, it was demonstrated that transition metal nitrides such as TiN can be grown as a constituent of single-crystal thin-film epitaxial metal/semiconductor superlattices with low defect densities exhibiting high melting points and mechanical hardness for applications as hard coatings and high-temperature thermoelectric materials [22][23][24][25][26][27][28]. In addition to its high chemical and thermal stability, a TiN/(Al,Sc)N multilayer architecture with metal/dielectric interfaces has been proven a promising hyperbolic metamaterial in the visible spectral range and demonstrated large enhancement of its densities of photon states which could be useful in various quantum electronic and optoelectronic applications [29,30].…”