Hall measurements were made of highly strained modulation-doped InAs quantum-wells which had been grown, by molecular-beam epitaxy, onto GaAs(110) substrates. The structures exhibited appreciable anisotropic strain relaxation, with an interfacial misfit dislocation network which consisted of 90º dislocations along the in-plane [001] direction, and 60º dislocations along the perpendicular [1¯10] direction. It was noted that, whereas the linear density of the former was essentially independent of strain, that of the 60º dislocations increased with thickness of the InAs layer. By using samples which were patterned with a so-called bridge Hall-bar geometry, and had current channels aligned along the dislocation lines, very low anisotropic mobilities were found; with those in the [1¯10] direction being consistently higher than those along [001]. Higher than expected carrier densities, as compared with self-consistent calculations, were also measured in the samples. Both of the effects appeared to be directly related to the degree of relaxation in the structures and, in particular, to the density of 60º misfit dislocations at the quantum-well interfaces. The results showed that 60º dislocations were more effective in scattering than were 90º dislocations. It was suggested that the 60º dislocations possessed a significant line-charge, while the 90º dislocations were electrically neutral. Evidence was also found for donor-like behavior at the InAs/GaAs interface. This was attributed to pinning, by defects, of the Fermi level in the conduction band.

Electrical properties of highly strained modulation-doped InAs/GaAs(110) quantum-well heterostructures R.Jaszek, J.J.Harris, C.Roberts: Journal of Applied Physics, 1999, 85[2], 959-68