A gradient in the composition of at least one of the elements of a metal-based semiconductor layer is introduced as a function of depth through the layer. The gradient(s) influence the current density response of the device at different gate voltages. In some embodiments, the composition of an element (e.g. Ga) is greater at the interface between the metal-based semiconductor layer and the source/drain layers. The shape of the gradient profile is one of linear, stepped, parabolic, exponential, and the like.