GaAs integrated microwave circuits

GaAs has many desirable features that make it most useful for microwave and millimeter-wave integrated circuits. The process of selective epitaxial depositions of high purity single-crystal GaAs with various doping concentrations into semi-insulating GaAs substrates has been developed. These high-resistivity substrates (>10
⁶
ohm.cm) provide the electrical isolation between devices, eliminating the difficulties and deficiencies normally encountered in trying to obtain isolation with dielectrics, back-etching, p-n junctions, etc. This monolithic approach to integrated-circuits thus allows for improved microwave pedormance from the devices since parasitics are reduced to a minimum. Planar Gunn oscillators and Schottky barrier diodes have been fabricated for use in a completely monolithic integrated millimeter wave (94 GHz) receiving front end. The Gunn oscillators are made in a sandwich-type structure of three selective deposits whose carrier concentrations are approximately 10
¹⁸
-10
¹⁵
-10
¹⁸
cm
^-3
. The Schottky diodes consist of two deposits with concentrations of 10
¹⁸
and 10
¹⁷
cm
^-3
. The Schottky contact is formed by evaporating Mo-Au onto the 10
¹⁷
cm
^-3
deposits; all ohmic contacts are on the surface and are alloyed to the N
⁺
regions.