Enhanced microwave performance of ion-implanted MESFET with graded GaAs/AlGaAs heterojunctions

Ion-implanted MESFETs have been fabricated on an inverted GaAs/AlGaAs heterostructure. The aluminium concentration in the AlGaAs is graded from 0% at the substrate to 30% at the heterointerface. A maximum extrinsic transconductance of 410 mS/mm is achieved with 0.5 µm gate devices. This heterojunction ion-implanted FET (HIFET) also exhibits enhanced microwave performance, especially at low drain current, when compared to conventional ionimplanted GaAs MESFETs. At 20% of Idss the current gain cutoff frequency ftis 40 GHz, which increases up to a maximum value of 47 GHz as the drain current rises. These characteristics of high ft and high gain at low current are advantageous for low-noise applications.