In self-aligned ion implanted structure the Gate, Drain and Source are set down and they are generally metallic contacts, although the source and drain contacts may sometimes be made from germanium. There are two main structures that are the self-aligned ion implanted structure and the recess gate structure. The exact thickness of this layer is required and special techniques are required for the control of the thickness of this layer. The doped layer of Aluminium Gallium Arsenide about 500 Angstroms thick is set down above this as shown in the diagrams below. This is very critical if the high electron mobility is to be achieved. The main purpose of this layer is to ensure the separation of the Hetero-junction interface from the doped Aluminium Gallium Arsenide region. After that, a very thin layer between 30 and 60 Angstroms of intrinsic Aluminium Gallium Arsenide is set down on top of this layer. The manufacture of an HEMT as follows procedure, first an intrinsic layer of Gallium Arsenide is set down on the semi-insulating Gallium Arsenide layer.
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