MORPHOLOGICAL INSTABILITIES ON EXACTLY ORIENTED AND ON VICINAL GAAS(001) SURFACES DURING MOLECULAR-BEAM EPITIXY

A continuous spectrum of misorientations of all azimuthal angles and inclinations varying from 0 degrees to 8 degrees occurring on spherically shaped substrates was used to study the development of terrace-step structures of homoepitaxially grown GaAs (001) by reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM). The singular GaAs (001) surface shows growth instabilities with respect to the step-edge profile and the terrace width distribution ranging from 0.1 to 1 mu m. The vicinal surface is composed of straight Ga-terminated and ragged As-terminated steps reflecting the interplay of the different nature of both kinds of steps. Obviously, self-similar terrace and step structures are reproduced on different length scales as revealed by a comparison of the atomic force microscopy images with images known from scanning tunnelling microscopy. This scaling leads to terrace and step dimensions which are comparable to the length scale of electronic excitations, thus, influencing the electronic properties of the material. All surfaces under investigation showed a common lateral roughness on the 0.5 to 4 mu m scale caused by fluctuations of the terrace width distribution (two-dimensional step bunching). This lateral modulation length increases with increasing misorientation and is always larger, parallel to the [$($) over bar$$ 110] direction than perpendicular to this direction. The vertical roughness increases with the amount of misorientation and is stronger for misorientations towards ($($) over bar$$ 111)As.