Formation of nanostructured surfaces during molecular beam epitaxy on square-shaped hole and mesa patterns on GaAs(3 1 1)A substrates

The evolution of the surface morphology during molecular beam epitaxy on GaAs(3 1 1)A substrates patterned with square-shaped holes and mesas oriented along [0 1 (1) over bar] and [(2) over bar 3 3] is investigated. In the areas patterned with holes arrow-head like tip structures pointing towards the [2 (3) over bar (3) over bar] direction develop on the original substrate surface between the holes. The tips are formed at the pinch-off of two symmetrically arranged (1 1 I) planes tilted with respect to the orientation of the {3 3 1} sidewalls along [(2) over bar 3 3] of the hole. In the areas patterned with mesas similar structures develop, here in the top and bottom areas of the mesas. Detailed analysis reveal the surface morphologies to be related to the preferential migration of Ga adatoms from the symmetric {3 3 1} A sidewalls of the mesas and holes to the top and bottom regions together with the evolution of the nearby {1 1 1} side facets to produce very uniform arrays of triangular lateral tip structures. (C) 1998 Elsevier Science B.V. All rights reserved.