High-current GaAs/AlGaAs MODFETs with fTover 80 GHz

We have designed and fabricated single-well, double-heterojunction, MODFETs which show up to 80% larger drain current, and up to 30% higher fT, than a good single-heterostructure MODFET. These improved electrical properties result from a substantial increase in the two-dimensional electron density, achieved by augmenting a pulse-doped (1) MODFET with a second doping pulse buried in an AlGaAs/GaAs superlattice below the 2D channel. In this study, we varied the sheet dose of Si donors in the buried doping pulse from 0 to 2 × 10¹²cm^-2. The resulting increase in 2DEG sheet electron density allowed us to achieve maximum drain currents greater than 600 mA/mm for the buried pulses with highest doping, and values of fTas high as 82 GHz for a buried pulse with lower doping.