|Ph.D Student||Gan Lahav|
|Subject||Field Emission from Conductive Diamond Surfaces|
|Department||Department of Physics||Supervisor||Professor Emeritus Rafael Kalish|
|Full Thesis text|
This work presents the results of a study of the electrical properties of conductive hydrogen terminated (HT) diamond surfaces by electron field emission (FE) and other techniques. These measurements of surface conductivity of single crystal (SC), poly-crystalline and ultra nano crystalline diamonds (UNCD) reveals fundamental physical properties of this unique diamond surface conductivity.
Field emission measurements of HT SC IIa diamond conductive surfaces show discrete jumps, at room temperature, in the emitted current at well defined values of the electric field. These jumps are well reproduced by computation simulation based on the assumption that a 2D quantum system with discrete energy levels exists in the diamond near-surface layer. The present results confirm the formation of well-defined quantum states of holes in the 2D layer presents on HT air-exposed diamond surface. Photo-induced FE measurements show that not only these quantum states are populated by thermal exited electrons, but also this population can be enhanced by illumination. These photo-induced FE results, which show saturation in the emission current due to illumination, substantiate the quantum nature of this 2D system.
FE from HT undoped polycrystalline diamond show different behavior of the emission current compared to FE from HT SC and polycrystalline B-doped diamond. These differences are attributed to the differences in the surface roughness, and the difference in the conduction mechanisms. Fowler-Nordheim representation of the data for HT B-doped and un-doped polycrystalline diamond, shows that the Fermi energy at the HT diamond surfaces lies 0.34eV below the VBM.
Undoped UNCD, like diamond, can be rendered conductive by surface HT and exposure to air. However, unlike the surface conductivity of SC diamond, which has a flat surface, the UNCD surface is composed of many nano-diamond particles and intra-grain boundaries; therefore, the effect of grain boundaries on the conductivity should be considered. Indeed, the UNCD resistivity as a function of temperature exhibits yet unobserved double humped behavior. This is attributed to the combine effect of surface conductivity and that of inter-grain material. The latter exhibits variable range hopping in band tails, which is attributed to hoping conduction, in amorphous materials.
In summary, the novel observations and conclusions of this work not only shed new light on the understanding of electrical properties of diamond conductive surfaces, by substantiating that the surface accumulation layer does accommodate discrete energy levels, but they also pave new ways to study quantization effects at room temperature and new designs of future electronic devices.