CALCULATION OF ELECTRONIC-PROPERTIES OF DEFECTS IN DIAMOND - APPLICATION TO ELECTRON-EMISSION

Electron field emission from diamond or diamond coated surfaces has be en known experimentally to yield large currents at low fields. It has been speculated by the authors [Z.-H. Huang, P. H. Cutler, N. M. Misko vsky, and T. E. Sullivan, Appl. Phys. Lett. 65, 2562 (1994); J. Vac. S ci. Technol. B 13, 526 (1995)] that electron transport through band-ga p states can be responsible for sustaining such currents. These states may be generated by point and/or extended defects such as vacancies a nd grain boundaries in chemical-vapor-deposition diamond films. Electr onic and atomic properties of these defects are calculated using a tig ht binding approach. The model consists of a single vacancy or H subst itution in a repeated extended cell consisting of 27 carbon atoms. The presence of vacancies or H substitution produces states that are spat ially localized and whose energies lie in the gap. These states span a n energy spectrum of about 1-2 eV just above the top of the valence ba nd. The calculations for a concentration of about 10(19) cm(-3) sugges t that these defect states are too low in energy to couple to those st ates which can produce the tunneling current in field emission. Additi onal work is needed to clarify the transport mechanism and how it depe nds on vacancy concentration including the possibility of vacancy-vaca ncy interaction which can lead to broadening of the discrete states in to bands. (C) 1996 American Vacuum Society.