Morphology, surface core-level shifts and surface energy of the faceted GaAs(112)A and(112)B surfaces

The GaAs(112)A and ((112) over bar)B surfaces have been prepared by molecular-beam epitaxy (MBE) and analyzed in situ by low-energy electron diffraction (LEED) and surface core-level spectroscopy of the Ga 3d and As 3d core levels using synchrotron radiation. The morphology of these surfaces has been studied in situ by scanning tunneling microscopy (STM) and ex situ by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Neither of the surfaces is stable, but both decompose into facets under standard MBE preparation conditions. The (112)A surface is covered by regular depressions (inverted pyramids) with a pentagonal base and with side walls formed of low-energy (111), {110}, and as yet unobserved {124} facets. The (112) over bar B surface exhibits depressions with ((1) over bar (1) over bar (1) over bar), {0 (1) over bar (1) over bar}, and ((1) over bar (1) over bar (3) over bar) facets on a rectangular base. These results are in agreement with ab-initio calculations of surface energies based on density functional theory. The theoretical findings show that, by forming roof-like structures employing {110} or {111} and {113} surfaces, the surface free energy can be lowered below the values found for a large number of reasonable GaAs(112)A and ((1) over bar (1) over bar (2) over bar)B model surfaces. (C) 1999 Elsevier Science B.V. All rights reserved.