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 /sup 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 performance 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 (94GHz) receiving front end.The Gunn oscillators are made in a sandwich-type structure of three selective deposits whose carrier concentrations are approximately 10 /sup 18/ -10 /sup 15/ -10 /sup 18/ cm /sup -3/.The Schottky diodes consist of two deposits with concentrations of 10 /sup 18/ and 10 /sup 17/ cm /sup -3/.The Schottky contact is formed by evaporating Mo-Au onto the 10 /sup 17/ cm /sup -3/ deposits; all ohmic contacts are on the surface and are alloyed to the N+ regions.