PROPERTIES OF INTERFACES OF DIAMOND

Results related to two different interface aspects involving diamond are described: (1) the initial states of CVD diamond film growth, and (2) the negative electron affinity and formation of metal-diamond interfaces. The surface and interface properties are probed with STM, Raman scattering/photoluminescence and angle-resolved UV photoemission spectroscopy (ARUPS). STM measurements of diamond nuclei on Si after various plasma growth processes show both flat and hillocked structures characteristic of 2-dimensional and 3-dimensional growth modes, respectively. STS measurements show distinct I-V characteristics of the nuclei and the substrate. The presence of optical defects and the diamond quality are studied with micro-Raman/photoluminescence measurements. The results indicate an increased density of impurity-related defects during the initial stages of growth. The interface properties of Ti on natural crystal (111) and (100) surfaces are studied with ARUPS using 21.2 eV HeI emission. Prior to deposition the diamond (111) is chemically cleaned, and a sharp (0.5 eV FWHM) peak is observed at the position of the conduction band minimum, indicating a negative electron affinity surface. After a subsequent argon plasma clean this peak disappears, while the spectrum shows a shift of 0.5 eV towards higher energies. Upon sub-monolayer titanium deposition on (111) diamond, the negative electron affinity peak reappears. Further titanium depositions causes this titanium-induced negative electron affinity peak to be attenuated, indicating that the emission originates from the interface. A similar experiment, done on the diamond (100) surface, however, does not result in a negative electron affinity. By determining the relative positions of the diamond valence band edge and the titanium Fermi level, the Schottky barrier height of titanium on diamond is measured. A model, based on the Schottky barrier height of titanium on diamond, and the work function of titanium, is proposed for the observed titanium-induced negative electron affinity.