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

Abstract 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 2 O. Without any addition of water only Cu 3 N was obtained. Addition of water introduces oxygen into the Cu 3 N 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 2 O starts to deposit, in addition to an oxygen doped Cu 3 N phase. Only Cu 2 O is deposited at large excess of water. XPS and Raman spectroscopies indicated that the additional oxygen in the doped Cu 3 N structure occupies an interstitial position with a chemical environment similar to that of oxygen in Cu 2 O. The oxygen doping of the Cu 3 N phase did not influence the lattice parameter, which was close to the bulk parameter value of 3.814A. 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 3 N 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%).