Efficient nitrogen incorporation into amorphous carbon films by double beam method

Conductivity of amorphous carbon (a-C) was successfully controlled by incorporation of nitrogen atoms using a double beam method (DBM), where both rf nitrogen radical and rf methane plasma sources were controlled separately to optimize the nitrogen incorporation. The as-grown a-C is p-type with a conductivity of 10^-11 Ωcm and activation energy (E_a) of 333 meV. The addition of nitrogen atoms under varying nitrogen flow rate from 0 to 2.0 sccm caused the conductivity to reach 10^-4 Ωcm as maximum and E_a of 41 meV at 1.5 sccm. The optical band gap is shown to vary only marginally from standard of the as-grown of a-C film (1.39 eV) to 1.45 eV by nitrogen incorporation. The depth profile of a secondary ion mass spectroscopy (SIMS) shows that the uniform concentration of C and N in the films and the sharp interface between nitrogen doped and undoped regions from the doped/undoped sandwich-like a-C structure. Furthermore, the changes in the chemical structure and relative bond fractions as a function of nitrogen flow rate are reported based on the results of an X-ray photoelectron spectroscopy and a Raman spectroscopy.