Graded heterojunction ion-implanted FETs: a combination of heteroepitaxy and ion implantation

FETs fabricated by ion implantation into inverted GaAs-AlGaAs heterostructures grown by MOCVD are discussed. The AlAs fraction in the AlGaAs layer is graded from 0% at the substrate to 30% at the heterointerface. 0.5- mu m gate devices fabricated with the graded heterojunction show two transconductance peaks that are both greater than 420 mS/mm. These devices also exhibit enhanced power gain, especially at low drain current, when compared with conventional ion-implanted GaAs MESFETs. The f/sub t/ of the graded heterojunction device is relatively insensitive to the gate bias. At 20% of I/sub dss/, the measured extrinsic f/sub t/ is 40 GHz, which increases slightly up to 47 and 41 GHz at 50 and 100% of I/sub dss/, respectively. Electron accumulation at the graded GaAs-AlGaAs heterointerface leads to improve device performance at low current bias. >