Phase stability and oxygen doping in the Cu–N–O system

A growth stability diagram for the CuNO system has been determined in the temperature range 250–500 °C for a thermally activated CVD process, based on copper (II) hexafluoroacetylacetonate (Cu(hfac) 2), NH 3 and H 2O. Without any addition of water only Cu 3N was obtained. Addition of water introduces oxygen into the Cu 3N structure to a maximum amount of 9 at% at a water/nitrogen molar ratio of 0.36 at 325 °C. Above this molar ratio Cu 2O starts to deposit, in addition to an oxygen doped Cu 3N phase. Only Cu 2O is deposited at large excess of water. XPS and Raman spectroscopies indicated that the additional oxygen in the doped Cu 3N structure occupies an interstitial position with a chemical environment similar to that of oxygen in Cu 2O. The oxygen doping of the Cu 3N phase did not influence the lattice parameter, which was close to the bulk parameter value of 3.814Å. The film morphology varied markedly with both deposition temperature and water concentration in the vapour during deposition. Increasing the water concentration results in less faceted and textured films with smoother and more spherical grains. The resistivity of the Cu 3N films increased with increased oxygen content of the film and varied between 10 and 100 Ω cm (0–9 at% O). The optical band gap increased from 1.25 to 1.45eV as the oxygen content increased (0–9 at%).