Revisiting Effects of Nitrogen Incorporation and Graphitization on Conductivity of Ultra-nano-crystalline Diamond Films

Abstract

Detailed structural and electrical properties of ultra-nano-crystalline diamond (UNCD) films grown in H2/CH4/N2 plasma were systematically studied as a function of deposition temperature (T d ) and nitrogen content (% N2) to thoroughly evaluate their effects on conductivity. T d was scanned from 1000 to 1300 K for N2 fixed at 0, 5, 10 and 20 %. It was found that even the films grown in the synthetic gas mixture with no nitrogen could be made as conductive as 1-10 −2 Ω cm with overall resistivity of all the films tuned over 4 orders of magnitude through varying growth parameters. On a set of 27 samples, Raman spectroscopy and scanning electron microscopy show a progressive and highly reproducible film material phase transformation, from ultra-nano-crystalline diamond to nano-crystalline graphite as deposition temperature increases. The rate of this transformation is heavily dependent on N2 content. Addition of nitrogen greatly increases the amount of sp 2 bonded carbon in the films thus enhancing the physical connectivity in the GB network that have high electronic density of states. However, addition of nitrogen greatly slows down crystallization of sp 2 phase in the GBs. Therefore, proper balance between GB connectivity and crystallinity is the key in conductivity engineering of (N)UNCD.