Pulse doped MODFET's

We have designed and fabricated a novel variation of the conventional modulation-doped heterostructure FET, based on growth by molecular beam epitaxy. The doping of the AlGaAs is confined to a thin layer, about 100Å thick, close to the heterointerface. This increases the forward voltage of the Schottky gate, reduces the dependence of threshold voltage on MBE growth parameters, allows the use of high doping levels without excessive gate leakage, and reduces trapping effects associated with silicon incorporation into AlGaAs. Extrinsic transconductances greater than 300 mS/mm and Ft's greater than 33 GHz (for a 0.8 µm gate length) have been measured at room temperature.