TUNNELING SPECTROSCOPY ACROSS GAAS ALXGA1-XAS INTERFACES AT NANOMETERRESOLUTION/

The transition region at the interface of GaAs/AlxGa1-xAs multilayers grown by molecular-beam epitaxy is investigated on the (110) face usin g scanning tunneling microscopy and spectroscopy. An interface region of 2 to 3 unit cells is observed in the charge-density contours. The t unneling spectroscopy data, on the other hand, yield a transition regi on of 6 to 9 unit cells wide, as determined from the offset of the val ence-band edge. The experimentally derived valence-band position compa res well with theoretical calculations, provided the tip-induced elect rostatic band bending in the semiconductor layers is taken into accoun t.