Growth, Characterization and Device Development in Monocrystalline Diamond Films

摘要

Photoemission and field emission from p-type natural diamond crystals aredependent on the surface termination. Hydrogen termination results in a negative electron affinity (NEA) while O and adsorbate-free surfaces exhibit positive electron affinities. Thin metal layers can induce an effective NEA which can be modeled in terms of the metal workfunction and the metal-diamond Schottky barrier. NEA surfaces of p-type diamond are shown to exhibit emission with lower voltages. Nitrogen-doped films exhibited very high threshold fields, indicating different processes for insulating and p-type diamond. Current-voltage characteristics of tip-shaped molybdenum field emitters were investigated before and after coating with diamond or graphite powders. Stable emission was observed only after annealing and formation of a conductive Mo carbide layer at the metal-coating interface. Both coated emitters displayed enhanced emission and a reduction by a factor of two in the 'turn-on' voltages as compared to the uncoated emitters. For the graphite coated emitter, the enhancement was attributed to an increase in the field enhancement factor due to the coating morphology. Roughening of the Mo-diamond interface via carbide formation during the annealing step is presumed to have caused the enhanced emission for the diamond coated emitter. The transmission probabilities for the Mo-diamond and diamond-vacuum interface were calculated, using the WKB method, based on an emission mechanism from the intrinsic diamond's conduction band minimum. With a field locally enhanced to 100,000,000 V/cm, the transmission probability for the diamond-vacuum interface was 108 times larger than that of the Mo-diamond interface. This evaluation confirmed that the electron affinity of the diamond surface is not a governing factor in the emission from intrinsic diamond.