Nitrogen doping effects on electrical properties of diamond films

Chemical-vapor-deposited (CVD) diamond films with intentional nitrogen doping have been characterized by various standard techniques. Electrical resistance measurements demonstrate that the nitrogen doping significantly varies the surface conductivity of as-grown diamond films; the surface resistance of N-doped diamond films can reach as high as 10(11) Ohm, which is about six orders of magnitude higher than that of an undoped one. Such high surface resistance remains stable even after 8 hours of exposure to hydrogen plasma. It is also found that the photoemission threshold energy of N-doped diamond films is about 0.55 eV less than the diamond band-gap energy, which implies the existence of compensated surface gap states and possibly, negative electron affinity in the as-grown N-doped diamond films. The particular properties observed in the N-doped diamond films are discussed in relation to the fabrication of diode-type diamond electron emitters.