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 nickel on both diamond (111) and (100) surfaces, as a function of surface preparation. The Schottky barriers of thin (<5) nickel films on natural type-IIb (p-type semiconducting) diamond (111) and (100) surfaces were determined with ultraviolet photoemission spectroscopy. Exposing the diamond (111) surfaces to an argon plasma while heated to 350°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. Deposition of a monolayer of nickel on the hydrogen-free diamond (111) surface resulted in a Schottky barrier height of 0.5 eV. The nickel caused 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 1.0-eV Schottky barrier height. Diamond (100) surfaces were prepared by vacuum annealing to temperatures ranging from 500°C to 1070°C. The various anneals resulted in a lowering of the electron affinity by up to 1 eV, which resulted in a negative electron affinity after the surface had been annealed to 1000°C. Oxygen was initially present on the surface but could not be observed after the 1000°C anneal. The removal of oxygen and the appearance of a negative electron affinity coincided with the appearance of a 2×1 surface reconstruction. Nickel was deposited after the various anneals, and Schottky barrier heights were found, ranging from 1.5 eV for the 545°C-annealed surface to 0.7 eV for the 1070°C-annealed surface. These measurements suggest that for both the (111) and the (100) diamond surfaces the presence of chemisorbed species, such as hydrogen and oxygen, results in an increase in the Schottky barrier height.