Nitrogen modification of hydrogenated amorphous carbon films

Abstract

The effect of nitrogen addition on the structural and electronic properties of hydrogenated amorphous carbon ͑a-C:H͒ films has been characterized in terms of its composition, sp 3 bonding fraction, infrared and Raman spectra, optical band gap, conductivity, and paramagnetic defect. The variation of conductivity with nitrogen content suggests that N acts as a weak donor, with the conductivity first decreasing and then increasing as the Fermi level moves up in the band gap. Compensated behavior is found at about 7 at. % N, for the deposition conditions used here, where a number of properties show extreme behavior. The paramagnetic defect density and the Urbach tailwidth are each found to decrease with increasing N content. It is unusual to find alloy additions decreasing disorder in this manner.

Influence of sp2 clusters on the field emission properties of amorphous carbon thin films

“…[4,17] It can be seen from Fig. 3 (a) that E th drops with addition of N similar to that reported elsewhere [4,16] but in contrast to the DLC films of Silva et al, [18] no reduction in N s is observed (Fig 3 (b)). The reduction in N s in the DLC films was attributed to the passivation of defects as evidenced by the initial increase in the Tauc gap followed by a subsequent decrease.…”

Self-texturing of nitrogenated amorphous carbon thin films for electron field emission

“…15,16 A hydrocarbon containing gas mixture of CH 4 /He/N 2 was dissociated at a rf power of 30 W to deposit a-C:H:N films on highly doped ͑0.01-0.001 ⍀ cm͒ n-Si substrates. The films were deposited on substrates held at room temperature, and the properties of the films can be found in the literature.…”

“…The films were deposited on substrates held at room temperature, and the properties of the films can be found in the literature. 16 Nitrogen in amorphous carbon films is shown to act at a weak donor and alters the joint density of states in the films. Field-emission measurements were carried out using a parallel plate configuration with the film being the cathode and an ITO coated glass the anode placed 50 m from the cathode using glass fiber spacers.…”

“…% N, respectively. 16 All the films in this study were deposited under very similar conditions ͑i.e., the same dc selfbias voltage and pressure in the rf PECVD process͒ on substrates held at room temperature. Therefore, the change in texture cannot be attributed to either the ion energy of the CH ion species or the substrate temperature.…”

“…It has been shown that N incorporated into a-C:H films acts as a weak donor state that moves the activation energy from ϳ0.8 to ϳ0.5 eV from the conduction-band edge for the 1.8-2.0 eV band-gap films analyzed in this study. 16 The conductivity of the a-C:H:N films is, therefore, still very low (ϳ10 Ϫ5 ⍀ Ϫ1 cm Ϫ1 ) at room temperature and cannot sustain a high conduction current through the film at low electric fields. However, since there is a weak doping effect, with the increased atomic N content in the films, it is more likely for there to be space-charge-induced band bending in the fully depleted a-C:H:N film due to an increased ionized donor concentration in the films due to the presence of the n ϩϩ -Si/a-C:H:N heterojunction, as discussed previously.…”