Theoretical reflectance anisotropy spectroscopy and scanning tunnelling microscopy study of the gaas(001) (2 × 4) surface

The method of reflectance anisotropy spectroscopy (RAS) has proved extremely useful in monitoring the structure of semiconductor surfaces during growth under metal-organic vapour phase epitaxy conditions. Similarly, scanning tunnelling microscopy (STM) has proved invaluable in providing information in real space, with atomic resolution, to determine surface atomic structure. It is therefore clear that the combination of these two techniques could provide vital evidence in determining the reconstructions of the GaAs(001) (2 × 4) surface. Both techniques, however, suffer from the lack of supporting theoretical calculations. This is necessary for an analysis of the RAS spectra and for an interpretation of the STM images. Using an ab initio pseudopotential method we have calculated the RAS spectra and generated STM images for three different models of the GaAs(001) surface. We are thus able to provide a link between theoretical RAS spectra, STM images and experiment.