Anisotropic Hall mobilities of a two-dimensional electron gas are observed in modulation-doped ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs heterostructures grown by molecular-beam epitaxy on a (001) GaAs substrate. The mobility in the [1¯10] direction is larger than that in the [110] direction. An anisotropic interface roughness is proposed to account for the observed anisotropic Hall mobilities. The dependences of the anisotropic mobilities on the electron concentration are explained well by the theoretical calculation, which assumes the existence of interface islands longer in the [1¯10] direction than in the [110] direction. This assumption is consistent with previous reports on in situ measurement of growing surfaces by scanning tunneling microscope and electron diffraction.

• Received 30 September 1992

DOI:https://doi.org/10.1103/PhysRevB.46.15558