Electron transport anisotropies in pseudomorphic InGaAs channel materials and their structural origin

Measurements of the electron transport properties in In x Ga 1− x As ( x = 0.2 and x = 0.3) channel heterostructures have consistently shown the transport mobility to be higher in the [01&1macr;] direction compared to [011] on a (100) wafer. Low temperature (1.6 K) measurements of these materials show that the mobility difference can be as large as 30% whilst the differences in carrier concentrations for the two directions are negligible in comparison. The mobility anisotropy decreases to below 5% at room temperature as the effects of phonon scattering, which is isotropic, begin to dominate. The anisotropy in the quantum mobility is much less pronounced than that in the transport mobility. This suggests that the low mobility in the [011] direction is primarily a result of large angle scattering. Transmission electron microscopy (TEM) analysis was performed on cross‐sections of material in the two directions. Thickness fluctuations in the channel were observed whilst traversing the channel of a (01&1macr;) section in the [011] direction where as none were observed in (011) sections along the [01&1macr;] direction. The length scale of the fluctuations was variable but typically around 50–100 nm. Transport simulations reveal that a 1‐dimensional potential modulation with a wavelength similar to that of the fluctuations produces a mobility anisotropy with the observed sign. Therefore it is likely that the thickness variations, possibly combined with synchronous fluctuations in the indium concentration along the [011] direction, are responsible for the reduced mobility in [011] transport. Although to the best of our knowledge these thickness fluctuations are reported here for the first time, similar growth anisotropies are well known for In x Ga 1− x As layers deposited on InP. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)