SURFACE-MORPHOLOGY DURING STRAIN RELAXATION IN THE GROWTH OF INAS ON GAAS(110)

Scanning tunnelling microscopy has been used to investigate dislocatio n-induced surface morphological changes during strain relaxation in th e two-dimensional (2D) growth of InAs on GaAs(110) by molecular beam e pitaxy. Two distinct classes of dislocation are required owing to the crystallographic anisotropy in the (110) plane: ideal edge dislocation s (similar to 3 ML) and dislocation half-loop slip (> 5 ML) systems. S pecific emphasis is on the nucleation of the edge dislocations out of the preceding pseudomorphic layer and the manner in which the slip ste ps accommodate the continuing growth of the epilayer and influence the surface morphology. Between 1 and 2 ML InAs thickness, a substantial redistribution of the surface material occurs, leading to highly unifo rm ''mosaic'' structures, which are either close-packed arrays of tiny islands at similar to 420 degrees C, or a linear array at similar to 480 degrees C. The closure of these fractured morphologies directly in corporates edge misfit dislocations beneath the original boundaries be tween the surface islands. Since a slip mechanism cannot operate for [ 110] strain relief, the dislocations must be located directly beneath the surface, a layer or so above the InAs-GaAs interface. Distinctive step signatures due to the slip of surface-nucleated half-loop disloca tions, in terms of the screw terminations and their associated wave li ke topological profiles, are observed after 5 ML InAs deposition. The growth mode for the InAs layer beyond 5 ML is by propagation of the sl ip steps, with discrete 2D island nuclei never observed. The slip step s can therefore move across the surface in the [001] direction away fr om their original position, as well as increasing in length as the dis location half-loops expand along the [<1(1)over bar>0] direction. The linear density of slip steps along [001] decreases with increasing fil m thickness due to interaction of the steps during growth. The length of each slip step and of each misfit segment is relatively short (less than or equal to 1000 Angstrom) in comparison with growth on (001) su bstrates. A related interaction between the hair-loop and preceding ed ge dislocations at the interface is also resolved. (C) 1998 Elsevier S cience B.V. All rights reserved.