PROPERTIES OF INTERFACES OF DIAMOND

Results related to two different interface aspects involving diamond a re described: (1) the initial states of CVD diamond film growth, and ( 2) the negative electron affinity and formation of metal-diamond inter faces. The surface and interface properties are probed with STM, Raman scattering/photoluminescence and angle-resolved UV photoemission spec troscopy (ARUPS). STM measurements of diamond nuclei on Si after vario us plasma growth processes show both flat and hillocked structures cha racteristic of 2-dimensional and 3-dimensional growth modes, respectiv ely. STS measurements show distinct I-V characteristics of the nuclei and the substrate. The presence of optical defects and the diamond qua lity are studied with micro-Raman/photoluminescence measurements. The results indicate an increased density of impurity-related defects duri ng the initial stages of growth. The interface properties of Ti on nat ural 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 o f 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. Up on sub-monolayer titanium deposition on (111) diamond, the negative el ectron affinity peak reappears. Further titanium depositions causes th is 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 resul t in a negative electron affinity. By determining the relative positio ns of the diamond valence band edge and the titanium Fermi level, the Schottky barrier height of titanium on diamond is measured. A model, b ased on the Schottky barrier height of titanium on diamond, and the wo rk function of titanium, is proposed for the observed titanium-induced negative electron affinity.