The Fabrication of Very Short Gate-Length GaAs Field Effect Transistor Devices

The object of the work described in this thesis was to fabricate GaAs Metal-Semiconductor Field Effect Transistors with gate lengths comparable with the smallest structures fabricated previously in this Department using electron beam lithography. It was envisaged that MESFETs would be fabricated on both solid substrates and on thin active membranes of GaAs. It was then hoped to transfer the technology developed for the fabrication of MESFETs to the fabrication of High Electron Mobility Transistors (HEMTs). A substantial part of the work was devoted to the development of a low temperature contact technology which could be used for the formation of ohmic contacts to GaAs. The low temperature was thought to be necessary to prevent undesired diffusion of the contact material during annealing, particularly on devices with closely spaced drain-source contacts. It was found that by varying the contact composition, a reduction in optimum annealing temperature of over 10