Electron scattering by steps in a vicinal heterointerface

Anisotropic Hall mobilities of a two-dimensional electron gas are observed in modulation-doped ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}/\mathrm{GaAs}$ heterostructures grown on a (001) GaAs vicinal substrate cut 2° toward the $\mathrm{}\left(111\right)A$ direction. The mobility is larger in the [$\overline{1}10$] direction. There is no anisotropy in mobilities for a sample grown on a 2° vicinal substrate toward the $\mathrm{}\left(111\right)B$ direction. Electron scattering by an array of steps is proposed to account for the observed anisotropic Hall mobilities. The electron concentration dependence of mobility anisotropy implies that the origin of step potential is not interface roughness but localized dipole.