Characterization of thin active layer on semi-insulating GaAs by mapping of FET array performance

A computer-aided FET performance measurement system was established to characterize a thin active layer formed on a semi-insulating GaAs substrate. By mapping FET array performances on a thin active layer, this system was applicable to substrate material quality evaluation and to a check of FET fabrication processes. It also gave the key information on FET threshold voltage scattering to the GaAs IC circuit designer. Most importantly, it was powerful in the characterization of thin active layers for which conventional methods, such as resistivity, Hall, or C-V measurements, were not effective because of the surface depletion layer into the thin active layer. It is demonstrated that dislocations in substrate crystal were clearly revealed to affect FET threshold scattering on the active layer formed by direct ion implantation on an LEC-grown semi-insulating substrate.