Charge Scattering Mechanisms in shallow InAs quantum wells*

We studied the charge scattering mechanisms present in In_0.2Al_0.8Sb/InAs/Al_0.8Ga_0.2Sb wells placed in close proximity to the surface of the heterostructures, at depths from 7 nm to 15 nm. The heterostructures were either unintentionally-doped, doped from below the channel or from above the channel. Measurements of sheet and Hall resistances were performed at T = 2K in variable magnetic field and under illumination with wavelengths of 400 nm up to 1300 nm. The charge density dependencies of the Hall mobility and quantum scattering time were used to infer the dominant mechanisms. We found that the transport quality of the sample is dominated by bottom interface roughness, and that reducing the asymmetry of the potential well results in improved charge transport as the scattering of interface roughness is reduced. This is, however, detrimental to the strength of spin-orbit coupling and to spin-based applications of these materials