Metamorphic In/sub 0.3/Ga/sub 0.7/As/In/sub 0.29/Al/sub 0.71/As layer on GaAs: a new structure for millimeter wave ICs

A new high electron mobility transistor (HEMT) using InAlAs/InGaAs grown on GaAs has been successfully realized. This device, with an In content close to 30%, presents several advantages over conventional pseudomorphic HEMT on GaAs and over lattice matched HEMT on InP. To accommodate the mismatch between the active layer and the GaAs substrate, a metamorphic buffer has been grown at low temperature. High electron mobility with high two dimensional electron gas density (25000 cm/sup 2V.s with 3/spl times/10/sup 12/ cm/sup -2/ at 77 K) as well as high Schottky barrier quality (Vb=0.68 V with /spl eta/=1.1) have been obtained. A device with a 0.4/spl times/150 /spl mu/m/sup 2/ gate geometry has shown a transconductance as high as 700 mS/mm at a current density of 230 mA/mm. The measured f/sub T/ was 45 GHz and f/sub max/ was 115 GHz. These values, showing the great potentiality of this structure, are, to the authors knowledge, the first reported for submicrometer gate metamorphic InAlAs/InGaAs/GaAs HEMTs with an indium content of 30%.<
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