Modification of transconductance characteristics for ion-implanted GaAs/AlGaAs heterojunction MESFETs

Abstract

Inverted GaAs/AlGaAs heterostructures grown by MOCVD have been used to fabricate conventional ion-implanted MESFETs. Two types of GaAs/AGaAs heterojunctions are studied. One type has a compositionally graded AlGaAs layer which provides a built-in field and corresponding quantum well at the heterointerface. The other type has a constant-composition AlGaAs layer. 0.5μm gate devices fabricated using the ungraded AlGaAs layer show a maximum extrinsic transconductance Gm of 280mS/mm and a small Gm variation over a gate voltage range of 1.5 V. In comparison, devices fabricated using the graded AlGaAs layer exhibit higher transconductance over all the gate voltages and an enhancement of Gm up to 420 mS/mm at low gate bias.