Complementary metal oxide semiconductor (CMOS) gate stack with high dielectric constant gate dielectric and integrated diffusion barrier

A diffusion barrier (and method for forming the diffusion barrier) for a field-effect transistor having a channel region and a gate electrode, includes an insulating material being disposed over the channel region. The insulating material includes nitrogen (N), and is disposed under the gate electrode. The insulating material can be provided either as a layer or distributed within a gate dielectric material disposed under the gate electrode.