The influence of nitrogen excess on the optical response of N-rich Cu 3 N films is reported. The optical spectra measured in the wavelength range from 0.30 to 20.00 µm have been correlated with the elemental film composition which can be adjusted in the nitrogen atomic percentage (at%) range from 27 ± 2 up to 33 ± 2. The absorption spectra for the N-rich films are consistent with direct optical transitions corresponding to the stoichiometric semiconductor Cu 3 N plus a free-carrier contribution

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... that can be tuned in accordance with the N-excess. The data are consistent with the incorporation of the excess N in the lattice as an electron acceptor that generates free holes.