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

摘要

A growth stability diagram for the Cu-N-0 system has been determined in the temperature range 250-500 ℃ 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 wateritrogen molar ratio of 0.36 at 325 ℃. 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.rnXPS 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 3.814A. 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_3N films increased with increased oxygen content of the film and varied between 10 and 100Ω cm (0-9 at% O). The optical band gap increased from 1.25 to 1.45eV as the oxygen content increased (0-9 at%).