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 i nclinations varying from 0 degrees to 8 degrees occurring on spherical ly shaped substrates was used to study the development of terrace-step structures of homoepitaxially grown GaAs (001) by reflection high-ene rgy electron diffraction (RHEED) and atomic force microscopy (AFM). Th e singular GaAs (001) surface shows growth instabilities with respect to the step-edge profile and the terrace width distribution ranging fr om 0.1 to 1 mu m. The vicinal surface is composed of straight Ga-termi nated and ragged As-terminated steps reflecting the interplay of the d ifferent nature of both kinds of steps. Obviously, self-similar terrac e and step structures are reproduced on different length scales as rev ealed by a comparison of the atomic force microscopy images with image s known from scanning tunnelling microscopy. This scaling leads to ter race and step dimensions which are comparable to the length scale of e lectronic 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 te rrace width distribution (two-dimensional step bunching). This lateral modulation length increases with increasing misorientation and is alw ays larger, parallel to the [$($) over bar$$ 110] direction than perpe ndicular to this direction. The vertical roughness increases with the amount of misorientation and is stronger for misorientations towards ( $($) over bar$$ 111)As.