High-field transport in amorphous carbon and carbon nitride films

The temperature and electric field dependence of the current density in hydrogenated amorphous carbon and carbon nitride sandwich devices show a T ^-1/4 dependence of the ohmic conductivity σ = σ⁰⁰ · exp[-(T₀/T)^1/4] characteristic of 3D hopping, a linear correlation between the apparent Lnσ⁰⁰(F) and T₀(F) values, and a F/T^3/2 scaling of σ(F,T). The F² dependence of Lnσ(F,T) at intermediate fields, provides similar values of the decay length γ^-1 of localized π state wavefunctions in a-CN_x:H (2.4 nm) and a-C:H (2.8 nm) films. The larger conductivity in nitrogen-rich alloys is attributed to a combined effect of N-induced increase in the π-state density and ordering of the sp² phase.