The transition region at the interface of GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As multilayers grown by molecular-beam epitaxy is investigated on the (110) face using scanning tunneling microscopy and spectroscopy. An interface region of 2 to 3 unit cells is observed in the charge-density contours. The tunneling spectroscopy data, on the other hand, yield a transition region of 6 to 9 unit cells wide, as determined from the offset of the valence-band edge. The experimentally derived valence-band position compares well with theoretical calculations, provided the tip-induced electrostatic band bending in the semiconductor layers is taken into account.

• Received 22 October 1991

DOI:https://doi.org/10.1103/PhysRevB.45.6946