Abstract

In0.7Al0.3As/InAs/In0.8Ga0.2As modulation-doped heterostructures on GaAs were characterized and HFETs were fabricated. A linearly graded InAlAs buffer was used to transform the lattice constant from that of GaAs to In0.8Ga0.2As Random surface morphology with scattered volcano-like deep holes was observed. The root-mean-square roughness value was 4-7 nm. Most dislocations were confined in the graded buffer and the maximum threading dislocation density in the HFET layers was estimated to be in the order of 106 cm-2. An electron mobility of 1.37.104 cm2/Vs with a carrier density of 1.88.1012 cm-2 at 300 K was achieved. HFETs with a 0.1 um gate length showed an extrinsic transconductance of 750 mS/mm, an extrinsic fT of 90 GHz and an fmax of 225 GHz.