A pronounced anisotropy is observed in the low-temperature mobility of a two-dimensional electron gas formed in an ${\text{In}}_{0.75}{\text{Ga}}_{0.25}\text{As}/{\text{In}}_{0.75}{\text{Al}}_{0.75}\text{As}$ quantum well grown on a GaAs substrate. We show that the mobility differences along [011] and $\left[01\overline{1}\right]$ directions are mainly due to In concentration modulations. Spatially resolved photoemission measurements show an asymmetric indium concentration modulation, correlated with the surface morphology observed by atomic force microscopy. A theoretical model considering conduction band energy modulations agrees well with the transport measurements. The identification of this mobility limiting mechanism allowed us to design and grow higher quality two-dimensional electron gases, needed for high indium content InGaAs device fabrication.

• Received 2 April 2008

DOI:https://doi.org/10.1103/PhysRevB.77.235307