Fabrication and microwave characterisation of aluminium free HEMT devices and subsequent performance comparison against conventional AlGaAs/InGaAs based devices

At the current time HEMT microwave devices used in commercial applications are based on the AlGaAs/InGaAs heterojunctions, grown on a GaAs substrate. A possible alternative is GaInP/InGaAs heterojunction again grown on a GaAs substrate. This system offers the following potential advantages: 1) higher mobility in the doped GaInP allowing a reduction in access resistance; 2) absence of DX centres, improving the noise performance; 3) no fabrication oxidation problems caused by the aluminium content in the current material employed; 4) retains GaAs as the substrate material (reducing industrial conversion considerations). The presentation will initially discuss the fabrication techniques which have been developed over the past year and a half to produce sub micron devices at Cardiff University. Subsequently microwave and DC data are presented comparing fabricated GaInP/InGaAs transistors of different structure and morphology against those fabricated using commercial AlGaAs/InGaAs material