Epitaxial NaCl structure {delta}-TaN{sub x}(001): Electronic transport properties, elastic modulus, and hardness versus N/Ta ratio

Journal Article · Sat Sep 15 04:00:00 EDT 2001 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.1391214· OSTI ID:40277795

Shin, C -S; Gall, D; Kim, Y -W; Desjardins, P; Petrov, I; Greene, J E; Oden, M; Hultman, L

While metastable B1-NaCl-structure {delta}-TaN{sub x} is presently used in a variety of hard coating, wear-resistant, and diffusion barrier applications, it is a complex material exhibiting a wide single-phase field, x{approx_equal}0.94--1.37, and little is known about its fundamental properties. Here, we report physical properties of epitaxial {delta}-TaN{sub x} layers grown as a function of x on MgO(001) by ultrahigh vacuum reactive magnetron sputter deposition. The room-temperature resistivity ({rho}=225 {mu}{Omega} cm), hardness (H=30.9 GPa), and elastic modulus (E=455 GPa) of {delta}-TaN{sub x}(001) are independent of x over the range 0.94--1.22. However, changes in the electronic structure associated with increasing x>1.22 lead to an increase in {rho} with a decrease in H and E. All {delta}-TaN{sub x}(001) layers exhibit negative temperature coefficients of resistivity between 20 and 400 K due to weak carrier localization. {delta}-TaN{sub x} is superconducting with the highest critical temperature, 8.45 K, obtained for layers with the lowest N/Ta ratio, x=0.94. Based upon the above results, combined with the fact that the relaxed lattice constant a{sub 0} shows only a very weak dependence on x, we propose that the wide phase field in {delta}-TaN{sub x} is due primarily to antisite substitutions of Ta on N (and N on Ta) sites, rather than to cation and anion vacancies. To first order, antisite substitutions in TaN{sub x} are isoelectronic and hence have little effect on charge carrier density. At sufficiently high N/Ta ratios, however, simple electron-counting arguments are no longer valid since large deviations from stoichiometry alter the character of the band structure itself.

• Sponsoring Organization: (US)
• OSTI ID: 40277795
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 6 Vol. 90; ISSN 0021-8979
• Publisher: The American Physical Society
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CATIONS
CHARGE CARRIERS
CRITICAL TEMPERATURE
DIFFUSION BARRIERS
ELECTRONIC STRUCTURE
HARDNESS
PHYSICAL PROPERTIES
TEMPERATURE COEFFICIENT
TRANSPORT
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