Carrier transport in partially relaxed In0.75Ga0.25 As/InP high electron mobility structures

By increasing the thickness of the strained In_0.75Ga _0.25As channel above the critical thickness (with lattice matched InAlAs buffer and barrier layers grown on InP), both 60° mixed dislocations and 90° edge dislocations form at the interface between the lower InAlAs layer and the InGaAs channel. Transmission electron microscopy measurements confirmed that the misfits nucleate at localized crystallographic defects that are not necessarily associated with substrate threading dislocations. The asymmetric distribution of the dislocations corresponds to differences in carrier scattering along different crystallographic directions as determined by magneto-transport measurements from Hall bar samples that were fabricated along the [110], [100] and [11¯0]. The highest mobility generally occurs in a direction that is perpendicular to the lowest misfit density; for thicker channels that include higher densities of the 90° dislocations, the mobility is strongly attenuated along all major crystallographic directions. Using quantitative mobility spectrum analysis at room temperature and 77 K, we determined that the scattering of the first sub-band electrons is slightly reduced at room temperature compared to low temperature, whereas the mobility of the electrons in the higher energy level actually increases with increasing temperature