Surface properties and field emission of boron nitride

摘要

Boron nitride (BN) and boron carbon nitride (BCN) films with various carbon (C) composition ratios are synthesized by plasma-assisted chemical vapor deposition. The electron affinity of the BN and BCN films is estimated from the threshold energy of the photoelectron yield and the bandgap energy. Negative electron affinity is observed for the BN film. On the other hand, the positive electron affinity is observed for the BCN films. It is found that a reduction in the electron affinity occurs due to N_2 plasma treatment rather than H_2 plasma treatment for the BCN film. Field emission characteristics of the BN and BCN nanofilms are investigated. The turn-on electric field of the electron emission does not increase in the region of the C composition ratio lower than 20 percent. Also shown is the turn-on electric field of the BCN nanofilm treated with N_2 or H_2 plasma. A variation in the field emission characteristics is related to the surface properties such as electron affinity and surface roughness in addition to the conduction band discontinuity between the BCN nanofilm and Si substrate. It is demonstrated that the BCN film emits electrons at a pressure as high as 8-l0 x l0~(-4) Torr at which field emission characteristics of the carbon nanotube degrade rapidly.