The fabrication sequences of GaAs MESFET and the characteristics of the fabricated MESFET are presented.
By LPE technique, a buffer layer was epitaxially grown on a semiinsulating substrate and followed by a n-type active layer in our lab. The expected carrier concentration of the active layer was 1.0 × $10^{17}cm^{-3}$. But the DC characteristics of MESFET fabricated with this wafer showed only a voltage-controlled resistor performance. The doping concentration calculated from C-V measurement was 5 × $10^{15}cm^{-3}$. It is assumed the active layer was damaged during fabrication processes. But the possibility that the active layer was not grown uniformly or it was really low doped is not excluded.
With Sumitomo wafer, 0.48um active layer 2 × $10^{17}cm^{-3}$ doped, it was possible to fabricate $Normally-^0n$ MESFET. More work is needed to reach this FET off state.
