. . "tructure according to another embodiment of the present invention; there is also shown a V.sub.D-I.sub.D relation for a device having aconventional structure;FIG. 4 is a schematic view of an insulated gate FET having a conventional structure;FIG. 5 is a schematic representation of an energy band for the structures according to the present invention;FIGS. 6(A) to 6(G) are schematic representations" . .