Thermal stability of the negative electron affinity condition on cubic boron nitride

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Abstract
We have verified that the condition of negative electron affinity (NEA) exists on hydrogen-terminated polycrystalline cubic boron nitride (c-BN) grown by the high-pressure high-temperature method using ultraviolet photoelectron spectroscopy. The NEA condition is thermally stable to 950 °C. At higher temperatures, the surface reverts to a positive electron affinity condition due to the desorption of surface bound hydrogen. Repeated annealing at high temperatures results in the degradation of the surface crystallinity, which manifests in the growth of a π→π* feature attributable to sp2-type bonds. Complete regeneration of initial valence band features and NEA conditions along with the suppression of the π→π* features can be achieved by subjecting the surface to atomic hydrogen etching. It is discovered that the He (II)-excited valence band spectra of c-BN display significant differences between the hydrogen-terminated and hydrogen-free surface.