Proximity effect of dislocations on GaAs MESFET threshold voltage

Spatial inhomogeneity of semi-insulating LEC-grown GaAs is currently a subject of considerable attention, and there have been contradictory reports that dislocations affect FET threshold voltage either directly or indirectly. Careful measurements of the threshold voltage are carried out in the vicinity of cellular dislocation networks, lineages, and the densely dislocated wafer periphery, which are dislocation distributions peculiar to LEC-grown GaAs crystals. The measurements were made in an attempt to verify the proximity effect of dislocations on the threshold voltage. It is concluded that, even though there is still ambiguity at very close gate-to-pit distances, the proximity effect is apparently observed only when the gate-to-pit distance is less than about 50µm. A threshold voltage difference between dislocation-free and dislocated areas is also demonstrated.