One approach targeting to reduce the impurities incorporation was use of all-N-coordinated Nb complexes as precursors, f.e. the homoleptic Nb(V) compound [Nb(NEt2)5]
(the first precursor of this kind tested as single MOCVD sources).[[i]] Black coatings were obtained at 300–500°C substrate temperatures in N2 or H2 atmosphere. However, phase composition was not clarified by XRD measurements, and their conductivity
was not tested. Later, [Nb(NEt2)4] and [Nb(NMe2)5] were tested as precursors for atmospheric pressure MOCVD of NbN films (using NH3 as the reactive gas): at 200–400°C temperatures amorphous N-rich phase Nb3N4 films were deposited (Nb:N ratio ~0.74), with O and C contaminants <3 at.-% , the layers had 103–104 μΩ·cm specific resistivities.[ii]
[i] K. Sugiyama, S. Pac, Y. Takahashi, S. Motojima, J. Electrochem. Soc., 1975, 122, 1545.
[ii] R. Fix, R. G. Gordon, D. M. Hoffman, Chem. Mater. 1993, 5, 614.