Electronic structure of copper nitrides as a function of nitrogen content

The nitrogen content dependence of the electronic properties for copper nitride thin films with an atomic percentage of nitrogen ranging from 26±2 to 33±2 have been studied by means of optical (spectroscopic ellipsometry), thermoelectric (Seebeck), and electrical resistivity measurements. The optical spectra are consistent with direct optical transitions corresponding to the stoichiometric semiconductor Cu3N plus a free-carrier contribution, essentially independent of temperature, which can be tuned in accordance with the N-excess. Deviation of the N content from stoichiometry drives to significant decreases from −5 to −50μV/K in the Seebeck coefficient and to large enhancements, from 10−3 up to 10Ωcm, in the electrical resistivity. Band structure and density of states calculations have been carried out on the basis of the density functional theory to account for the experimental results. ► Electronic structure of N-rich Cu3N ► Stoichiometric films behave as an intrinsic semiconductor. ► N excess drives to the introduction of a narrow band at the Fermi level. ► Decrease of the Seebeck coefficient when increasing nitrogen content ► Increase of the electrical resistivity when increasing nitrogen content