In this article results of Hall measurements on highly strained, modulation-doped InAs quantum-wells (QWs), grown by molecular beam epitaxy on GaAs (110) substrates are presented. These structures exhibit noticeably anisotropic strain relaxation, with an interfacial misfit dislocation network consisting of 90° dislocations along the in-plane [001] direction, and 60° dislocations along the perpendicular [11̄0] direction. While the linear density of the former is essentially independent of strain, that of the 60° dislocations increases with the thickness of the InAs layer. Using samples patterned with a bridge “Hall-bar” geometry and the current channels aligned along the dislocation lines, we find very low anisotropic mobilities, with those in the [11̄0] direction consistently higher than those along the [001]. When compared to self-consistent calculations, we also measure higher than expected carrier densities in these samples. Both effects appear to be directly related to the degree of relaxation in the structures and, in particular, to the density of 60° misfit dislocations at the QW interfaces. In terms of the dislocation scattering of carriers, our results show that 60° dislocations are more effective at scattering than 90° dislocations. We suggest the 60° dislocations possess a significant line charge, whereas the 90° dislocations are electrically neutral. We have also found evidence of donor-like behavior at the InAs/GaAs interface, which we associate with the known pinning by defects in InAs of the Fermi level in the conduction band.
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