Charge trapping effect at the contact between a high-work-function metal and Ta2O5 high-k dielectric

• Published in: Journal of physics. D, Applied physics Vol. 41; no. 10; pp. 105302 - 105302 (4)
• Main Authors: Novkovski, N, Skeparovski, A, Atanassova, E
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 21.05.2008; Institute of Physics
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Physics; Surface double layers, schottky barriers, and work functions; Charge carrier trapping; Voltage dependence; Work functions; Energy levels; Tantalum oxide; Space charge; High k dielectric; Current density; Metal-insulator contacts; Charge carrier injection
• DOI: 10.1088/0022-3727/41/10/105302
• ISSN: 0022-3727

Metal(Al,W,Au)-dielectric(tantalum oxide)-Si structures were studied at constant low current injection (J = 0.025-0.1 mA cm-2). It was found that in the case of an Au electrode the voltage required to maintain a constant current increases with the injection time up to a saturated value. The process is reversible, as was confirmed by repeating the injection after a 58 h long pause. The observed effect is attributed to discharging into the metal conduction band of the near interface traps with energy levels higher than the Au Fermi level at zero voltage and charging with electrons injected into the insulator during current injection. The traps are attributed to the cap type vacancies near the interface being more stable when positively charged in the case of a high-work-function metal, as previously found by Ramprasad by first principle total energy calculations.