  We calculated functions for the potential, Vch, in the channel of a field
effect transistor with various densities of the localized states (DOS) by using
a device simulator. In the saturation condition, Vch is found to fit
satisfactorily to the analytical function, Vch(y)=Vg(1-(1-y/L) k), where Vg is
the gate bias, y is the position along the channel, and L is the channel
length. The power k, which depends on the DOS, ranges from 0 to 0.5 even with
an extensive variation of DOS. As a result, the total induced charge density in
the saturation condition can be expressed a way similar to the linear condition
by introducing a correction factor, alpha, ranging between 0.65 and 1.0.
