Comparison of In0.33Al0.67As/In0.34Ga0.66As on GaAs metamorphic high electron mobility transistors grown by molecular beam epitaxy with normal and inverse step on linear graded buffer layers

Metamorphic high electron mobility transistors with 33% indium content have been grown on GaAs by molecular beam epitaxy. Linear graded InAlAs buffer layers were used to relax the mismatch strain between the InAlAs/InGaAs heterostructure and the GaAs substrate. The thickness of the graded buffer is shown to influence strain relaxation (tilt and residual strain), surface roughness, and Hall mobility. Furthermore insertion of an inverse step at the end of the grade by a finite reduction of the indium concentration reduces the residual strain and provides similar surface roughness with improved Hall mobility in the InGaAs channel.