Why does an Au cap on Pt lower the effective work function of a Pt-gated MOS (metal-oxide-semiconductor) stack?

03 March 2012 1 4K Report

The effective work function of the metal is measured for two MOS structures under the same conditions. Metal A - 100A Pt, metal B - 200A Pt capped with 3000A Au. The effective work function of the Pt/Au is ~0.3 eV lower. Why such a significant difference between uncapped and Au-capped Pt? I'd expect an impact of a capping layer on the work function after postmanufacturing thermal treatment, not before.

(EWF was determined from the voltage at peak dC/dV measurements)

Catherine Ellen Rice

The work function is the energy required to remove an electron from a metal surface to vacuum. Therefore, it is determined by the metal on top of the structure - at the surface. Thus it is understandable that a Au/Pt structure would have a different work function than one with Pt alone

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