Formation of a Mo2N skin layer in columnar-structural Mo films using NH3 plasma nitridation as the Se diffusion-barrier layer

Mo2N skin layers were formed on columnar-structural Mo films by simple NH3 plasma nitridation. The plasma-nitrided Mo (n-Mo) films contained the (111) preferred phase of γ-Mo2N phase and (112) preferred phase of β-Mo2N. The thickness of n-Mo films slightly increased without structural morphology change compared to that of pure-Mo films, and seldom changed after selenization. The electrical properties of the n-Mo films changed slightly compared to the Mo films after nitridation and the resistivity of the n-Mo films exhibited a slight increase after selenization. N-element was found widely along the z-axis of n-Mo films, and the concentration of N decreased gradually from the surface to bottom of Mo films. These results imply that the diffusion of N element occurred simultaneously along the lattice and grain boundaries (GB), which followed B-kinetics of Harrison's classification (GB width ≪ nitridation depth ≪ grain size). The n-Mo films exhibited the strong chemical stability under Se-environment, and the method developed in this study was an easy and effective technique for forming a Mo2N skin layer. Therefore, it is expected that this method can not only extend the process margin for selenization, but also reduce the resistive components in solar cell devices.