A NOVEL GAAS POWER MESFET WITH LOW DISTORTION CHARACTERISTICS EMPLOYING SEMIINSULATING SETBACK LAYER UNDER THE GATE

A low distortion GaAs power MESFET has been developed by employing a s emi-insulating setback layer under the gate, The setback region was ob tained by diffusing chromium from the Cr/Pt/Au gate metal in self-alig ned manner. The novel power FET with the setback layer was found to be insensitive to surface trapping effects, They showed only 5-6 percent 's frequency dispersion of drain current at 1 MHz compared to DC condi tion. Because of this small frequency dispersion, the typical measurem ent FET, which has the surface setback layer, with the gate width of 3 6 mm exhibited 1.5 dB larger output power at 1 dB gain compression poi nt than that of the FET without the setback layer, Moreover, in the pi /4 shift-QPSK modulation that has been most popular in digital mobile communication system, the FET exhibited 11 dB smaller adjacent channel leakage power than the conventional one at the output power of 31.5 d Bm.