MEASUREMENT OF THE SUBSTITUTIONAL NITROGEN ACTIVATION-ENERGY IN DIAMOND FILMS

We show that the electrical properties of nitrogen-doped nominally und oped polycrystalline chemical vapor deposited diamond films are modifi ed by post-deposition heating in an oxidizing atmosphere. We found tha t the first heating cycle in air in the temperature range of 300-673 K decreased the graphitization content still present in the diamond sur face and that after the second heating cycle the electrical resistance versus temperature curves became stabilized. Using a flow of argon wi th residues of oxygen over the surface of the sample during the heatin g cycles, the stabilization of the resistance-temperature dependence a lso occurred but only after the fourth heating cycle. The results sugg est the existence of an oxidation mechanism of the nondiamond carbon a toms present at the diamond surface. After stabilization, the deep don or ionization energy was found to be E-d= 1.62+/-0.02 eV. All results brought together strongly suggest that this level is due to single nit rogen atoms that occupy substitutional lattice sites in diamond. (C) 1 998 American Institute of Physics. [S0003-6951(98)01632-5].