Metamorphic InAlAs/InGaAs enhancement mode HEMTs on GaAs substrates

In/sub 0.5/Al/sub 0.5/As/In/sub 0.5/Ga/sub 0.5/As HEMTs have been grown metamorphically on GaAs substrates oriented 6/spl deg/ off [100] toward [111]A using a graded InAlAs buffer. The devices are enhancement mode and show good dc and RF performance. The 0.6-μm gate length devices have saturation currents of 262 mA/mm at a gate bias of 0.7 V and a peak transconductance of 647 mS/mm. The 0.6 μm×3 mm devices tested on-wafer have output powers up to 30 mW/mm and 46% power-added-efficiency (PAE) at 1 V drain bias and 850 MHz. When biased and matched for best efficiency performance, this same device has up to 68% PAE at V/sub d/=1 V.