INFLUENCE OF INTERFACIAL HYDROGEN AND OXYGEN ON THE SCHOTTKY-BARRIER HEIGHT OF NICKEL ON (111) AND (100) DIAMOND SURFACES

In this paper we report on Schottky barrier height measurements of nic kel on both diamond (111) and (100) surfaces, as a function of surface preparation. The Schottky barriers of thin (< 5 angstrom) nickel film s on natural type-IIb (p-type semiconducting) diamond (111) and (100) surfaces were determined with ultra-violet photoemission spectroscopy. Exposing the diamond (111) surfaces to an argon plasma while heated t o 350-degrees-C resulted in a change from a negative-electron-affinity surface to a positive-electron-affinity surface. This effect was used as an indication that a hydrogen-free surface had been obtained. Depo sition of a monolayer of nickel on the hydrogen-free diamond (111) sur face resulted in a Schottky barrier height of 0.5 eV. The nickel cause d the surface to exhibit a negative-electron-affinity surface. Nickel deposited on a diamond (111) surface with a negative electron affinity , indicative of a monohydride-terminated surface, resulted in a approx imately 1.0-eV Schottky barrier height. Diamond (100) surfaces were pr epared by vacuum annealing to temperatures ranging from 500-degrees-C to 1070-degrees-C. The various anneals resulted in a lowering of the e lectron affinity by up to approximately 1 eV, which resulted in a nega tive electron affinity after the surface had been annealed to approxim ately 1000-degrees-C. Oxygen was initially present on the surface but could not be observed after the 1000-degrees-C anneal. The removal of oxygen and the appearance of a negative electron affinity coincided wi th the appearance of a 2 X 1 surface reconstruction. Nickel was deposi ted after the various anneals, and Schottky barrier heights were found , ranging from 1.5 eV for the 545-degrees-C-annealed surface to 0.7 eV for the 1070-degrees-C-annealed surface. These measurements suggest t hat for both the (111) and the (100) diamond surfaces the presence of chemisorbed species, such as hydrogen and oxygen, results in an increa se in the Schottky barrier height.