Metamorphic In0.3Ga0.7As/In0.29Al 0.71As 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 cm²/V.s with 3×10¹² cm^-2 at 77 K) as well as high Schottky barrier quality (Vb=0.68 V with η=1.1) have been obtained. A device with a 0.4×150 μm² gate geometry has shown a transconductance as high as 700 mS/mm at a current density of 230 mA/mm. The measured f_T was 45 GHz and f_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%