ELECTROOPTIC CHARACTERIZATION OF MODULATION-DOPED FIELD-EFFECT TRANSISTORS WITH MONOLITHICALLY-INTEGRATED TEST FIXTURES

The authors report on the fabrication and electrooptic measurement of modulation-doped field-effect transistors (MODFETs) monolithically int egrated with coplanar stripline fixtures incorporating photoconductive switches. Both lattice-matched devices on InP substrates and pseudomo rphic devices on GaAs substrates, as well as two different gate access structures have been characterized. In comparing two devices with ide ntical gate access structures, one finds that the delay time of the ps eudomorphic device is almost twice as long as that of the lattice-matc hed device. Surprisingly, the switching times (drain output risetimes) of the two devices are comparable. One also sees that the gate access structure significantly affects the switching in two lattice-matched devices: the switching times for double-gate and single-gate contact d evices are 4.2 and 5.2 ps, respectively. In this case, however, no dif ference was seen in the delay times. These results show that, for the present devices, the switching and delay times are dominated by differ ent mechanisms.