Studies of field emission from bias-grown diamond thin films

We have investigated the field emission properties of diamond films grown under substrate bias conditions in a microwave plasma chemical vapor deposition system, with a substrate temperature of 800C, microwave power of 600 W, and a total pressure of 11 Torr. One group of films was grown with a substrate bias of -100 V in gas mixtures of 1% N₂ and 1%-20% CH₄ in H₂, while a second group of films was grown with a substrate bias ranging from +100 to -150 V in a gas mixture of 1%N₂-10%CH₄-89%H₂. The field emission performance in terms of threshold field and emission current improved considerably as a function of increasing CH₄ concentration and negative bias voltage. Ultraviolet Raman analysis showed that the field emission enhancement resulting from an increase in CH₄ concentration from 1% to 5% correlates with a decrease in the sp³ bonding character in the diamond film. The dependence of field emission on negative bias voltage appears to be correlated with ion bombardment-induced damage in the film during growth. The scanning electron microscopy image of the film grown with -150 V bias showed: smaller surface topographic features as compared to films grown under 0 and +100 V bias. The film grown with a bias of -150 V showed the lowest threshold field (∼2.0 V/μm) corresponding to an emission current density of 12.7 μA/cm². J vs E₀ measurements across a length of 40 mm over the film showed a uniform threshold field (2.0±0.55 V/μm). The film grown with a positive bias (+100 V) showed a relatively poor field emission performance.