THERMAL-STABILITY OF THE NEGATIVE ELECTRON-AFFINITY CONDITION ON CUBIC BORON-NITRIDE

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 ultravio let photoelectron spectroscopy. The NEA condition is thermally stable to 950 degrees C, At higher temperatures, the surface reverts to a pos itive electron affinity condition due to the desorption of surface bou nd hydrogen. Repeated annealing at high temperatures results in the de gradation of the surface crystallinity, which manifests in the growth of a pi-->pi, feature attributable to sp(2)-type bonds. Complete rege neration of initial valence band features and NEA conditions along wit h the suppression of the pi-->pi features can be achieved by subjecti ng the surface to atomic hydrogen etching, It is discovered that the H e (rr)-excited valence band spectra of c-BN display significant differ ences between the hydrogen-terminated and hydrogen-free surface. (C) 1 998 American Institute of Physics.