Formation of GaAs/AlAs(001) interfaces studied by scanning tunneling microscopy.

Abstract

We have investigated the interface formation of molecular-beam epitaxy (MBE) grown GaAs/AlAs(001) heterostructures by in situ scanning tunneling microscopy (STM) and reflection high-energy electron diffraction (RHEED). Starting from a smooth As-rich (2\ifmmode\times\else\texttimes\fi{}4) reconstructed GaAs surface the formation of the normal interface was studied at AlAs layer thicknesses ranging from 1 to 50 ML. With increasing AlAs thickness the reconstruction changes from (2\ifmmode\times\else\texttimes\fi{}4) to (2\ifmmode\times\else\texttimes\fi{}3) via a (1\ifmmode\times\else\texttimes\fi{}1) and a (1\ifmmode\times\else\texttimes\fi{}3) symmetry under the conditions used. For the inverted interface, the RHEED pattern changes immediately after the deposition of only 1 ML of GaAs on AlAs from a (2\ifmmode\times\else\texttimes\fi{}3) to a clear (2\ifmmode\times\else\texttimes\fi{}4) symmetry. The STM images of both interfaces show that the interface formation is accompanied by a disordering of the (2\ifmmode\times\else\texttimes\fi{}4) reconstruction by forming kinks in the missing dimer rows that can be related to intrinsic point defects. We attribute the different incorporation of these intrinsic point defects to the different electronic properties of the two interfaces. Large-scale STM images also reveal a different surface roughness for the normal and inverted interface. \textcopyright{} 1996 The American Physical Society.