Design of enhanced Schottky-barrier AlGaAs/GaAs MODFET's using highly doped p(+) surface layers

The design and performance of enhanced Schottky-barrier height modulation-doped AlGaAs/GaAs field-effect transistors (ESMODFETs) is discussed. Results are presented showing that the addition of a thin highly doped p(+) layer under the gate can increase the forward biased gate turn-on voltage from 0.8 V (conventional MODFET) to as high as 1.6 V. A mathematical model is presented that predicts the thickness and doping of the heterostructure layers required to obtain a given threshold voltage and effective Schottky-barrier height. It is predicted that this enhanced Schottky barrier will allow increased gate-voltage swings and thus significantly improve the noise margin of enhancement-mode MODFET circuits.