Fabrication of GaAs MESFET´s with non-alloyed ohmic contacts

Nonalloyed ohmic contacts to GaAs have previously been fabricated by the laser assisted diffusion of tin from a spin-on source. However, the resultant surfaces display poor morphology, especially after chemical etching. We have shown that critical surface areas may be protected with a thin (300-500 Å) layer of patterned silicon nitride, resulting in very smooth surfaces even after etching. Using this result we have fabricated MESFETs with patterned nonalloyed ohmic contacts to an ion-implanted channel. We have also used the lateral diffusion of dopants under the nitride layer to form channel and contact regions simultaneously, allowing gate, source, and drain metallization to be deposited in a single step. Preliminary RF and DC results on these MESFETs are presented.