Controlled formation of MoSe2 by MoNx thin film as a diffusion barrier against Se during selenization annealing for CIGS solar cell

This study investigated the interfacial reactions and electrical properties of a Mo single layer and Mo/MoNx/Mo multilayer during high temperature selenization annealing. The Mo single layer was converted easily to MoSe2, which was 7 times thicker than the Mo layer consumed ∼900 nm, by selenization at 460 °C for 10 min and the sheet resistance increased 8 fold compared to that of the as-deposited Mo film. On the other hand, in the Mo/MoNx/Mo structure, transmission electron microscopy (TEM) showed that the MoSe2 transformation was localized only in the top Mo layer and the bottom Mo layer was completely unaffected, even after selenization at 560 °C. The sheet resistance of the multilayer was relatively unchanged by selenization. This suggests that the MoNx layer performed well as a diffusion barrier against Se and the thickness of MoSe2 can be controlled precisely by adjusting the top Mo layer thickness. Furthermore, TEM and energy dispersive spectroscopy analysis showed that the selenized multilayer consisted of MoSe2/Mo/MoNx/Mo, in which the top Mo layer of 60 nm was not fully converted to MoSe2 and 20 nm was left unreacted. The residual Mo interlayer located at the interface of MoSe2 and MoNx is believed to be beneficial for the ohmic contact of the selenized multilayer.