Method for making a semiconductor device including a superlattice having nitrogen diffused therein

A method for making a semiconductor device may include forming a superlattice layer and an adjacent semiconductor layer. The superlattice layer may include a plurality of stacked groups of layers, with each group of layers comprising a plurality of stacked base semiconductor monolayers defining a base semiconductor portion, and at least one non-semiconductor monolayer constrained within a crystal lattice of adjacent base semiconductor portions. The method may further include diffusing nitrogen into the superlattice layer.