A multi-layer structure for use in the fabrication of integrated circuit
devices is adapted for the formation of enhancement mode high electron
mobility transistors, depletion mode high electron mobility transistors,
and power high electron mobility transistors. The structure has, on a
substrate, a channel layer, spacer layer on the channel layer, a first
Schottky layer, a second Schottky layer on the first Schottky layer, and
a third Schottky layer on the second Schottky layer, and a contact layer
on the third Schottky layer. Etch stops are defined intermediate the
first and second Schottky layers, intermediate the second and third
Schottky layers, and intermediate the third Schottky layer and the
contact layer.