Mechanism of field emission from chemical vapor deposited undoped polycrystalline diamond films

Field emission characteristics of undoped polycrystalline diamond films wit h different structural properties have been investigated. By introducing po sitive bias voltage and/or increasing CH4/H-2 ratio, the film quality is si gnificantly deteriorated together with the increase of nondiamond carbon co mponent and the surface morphologies of the films lost their unique facet s hape. The reason for the increase of nondiamond carbon content is described in terms of both the increase of substrate temperature and the excessive g eneration of CHn radicals. It is confirmed that an increase in the nondiamo nd carbon content markedly enhances field emission properties of diamond fi lms. From the spatial distribution of emission sites, it is suggested that the transport path of field-emitted electrons depends on the nondiamond car bon content: for the film with a large amount of nondiamond carbon, electro ns transport preferentially through the conducting mediums such as grain bo undaries while for the film with a relatively small amount of nondiamond ca rbon, electron transport occurs mainly through the diamond surface. (C) 200 0 American Institute of Physics. [S0021-8979(00)05510-9].