Conductive and resistive nanocrystalline diamond films studied by Raman spectroscopy

This paper shows what structural properties of amorphous non-diamond phases in nanocrystalline diamond films are responsible for the transition from resistive to conductive films. The films incorporated with nitrogen, oxygen, and hydrogen are prepared by microwave plasma chemical vapor deposition using Ar-rich gas mixtures. The amount, composition, and bonding properties of non-diamond phases are studied mainly by Raman spectroscopy and compared with the electrical resistivity of the films. The addition of N2 gas decreases the resistivity down to the order of 10− 2 Ω cm for deposition temperatures above a threshold of ∼ 1100 K. Non-diamond phases for high n-type conductivity are characterized by graphitic components with improved sp2 bond angle order for trivalent carbon atoms in addition to CN bonds. The addition of O2 or H2 gas promotes incorporation of oxygen or hydrogen into the films, not preferential etching of non-diamond phases. The resistivity increases or decreases largely by oxygen or hydrogen incorporation, respectively, then inversely changes by thermal annealing due to the deoxidization and dehydrogenation.