Nitrogen doping of amorphous carbon thin films

Abstract

Nitrogenated and hydrogenated amorphous carbon (a-C:H:N) films have been deposited by a plasma beam source using a gas mixture of C2H2 , Ar and N2 . The Ar/C2H2 ratio is kept constant at a ratio of 3, with the nitrogen flow allowed to vary. Nonnitrogenated films, with Ar/C2H2 ratios of 3 and 6 were also deposited and analyzed before attempting to identify the modifications to the microstructural properties due to nitrogen doping. The nitrogenated and hydrogenated a-C (a-C:H:N) films deposited in this study reveal interesting properties with regard to their optical gap, electrical conductivity, and mobility of the charge carriers. The optical E04 gap passes through a maximum of 2.7 eV as a function of incorporated nitrogen. The electrical conductivity, too, reaches a peak value of 1023(V cm)21 with increasing optical gap and remains constant for higher N2 flows. The electrical conductivity process is thermally activated with activation energies in the range 0.1–0.3 eV. This is discussed in terms of the mobility of the charge carriers ~determined by Hall measurements! and electronic doping. The defect density ~measured by electron spin resonance! is found to decrease with increasing nitrogen incorporation. The films have also been characterized by infrared spectroscopy, photo thermal deflection, and Raman spectroscopy. The microstructure of the deposited a-C:H:N films is discussed in terms of the electronic density of states.

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