Ultrathin Cu films on Si(111): Schottky barrier formation and sensor applications

Ultrathin Cu films were evaporated on Si(111) surfaces at substrate tempera tures of 175 K. By use of a microfabricated device structure, zero-force el ectrical contacts were formed on the thin Cu layers during evaporation. The y allowed current/voltage measurements of diodes with Cu films between 40 a nd 60 Angstrom. Although the rectifier properties are improved with increas ing thickness, the 60 rf diode still exhibits a large inhomogeneous interfa ce with a low barrier height of 0.47 eV and an ideality factor of 2.1. Anne aling the diode to room temperature leads to significant changes in the bar rier height which increases to 0.65 eV and the ideality factor which decrea ses to unity, suggesting a modification of the interface. The annealed thin -metal diodes may be used as atomic hydrogen sensors. A chemicurrent is obs erved in the diode when exposed to H atoms. The current is based on a nonad iabatic electron-hole pair creation which occurs during exothermic adsorpti on of hydrogen on Cu surfaces. (C) 1999 American Vacuum Society. [S0734-210 1(99)01604-8].