Structural, optical and electrical properties of reactively sputtered CrxNy films: Nitrogen influence on the phase formation

Abstract

The properties of various CrxNy films grown by direct current (DC) reactive sputtering process with different values of nitrogen partial pressures (0, 2x10(-4), 3.5x10(-4) and 5x10(-4) mbar) were studied. The structural analysis of the samples was performed by using X-ray diffraction and transmission electron microscopy (TEM), while an elemental analysis was realized by means of Rutherford backscattering spectrometry. By varying nitrogen partial pressure the pure Cr layer, mixture of Cr, Cr-2 N and CrN phases, or single-phase CrN was produced. TEM analysis showed that at pN(2) = 2x10(-4) mbar the layer has dense microstructure. On the other hand, the layer deposited at the highest nitrogen partial pressure exhibits pronounced columnar structure. The optical properties of CrxNy films were evaluated from spectroscopic ellipsometry data by the Drude or combined Drude and Tauc-Lorentz model. It was found that both refractive index and extinction coefficient are strongly dependent on the dominant phase formation (Cr, Cr-2 N, CrN) during the deposition process. Finally, the electrical studies indicated the metallic character of Cr-2 N phase and semiconducting behaviour of CrN.