Step-bunching instability in strained-layer superlattices grown on vicinalsubstrates

Epitaxial structures containing either compressive or tensile InGaAsP layer s separated by InP layers were grown on variously misoriented vicinal (001) InP substrates and studied by transmission electron microscopy. Except for zero misorientation, the compressive layers develop long-wavelength asymme trical lateral thickness modulations. We demonstrate that the associated su rface undulation consists of periodic bunches involving only the initial su bstrate steps. With increasing misorientation, the wavelength of the modula tion and its phase shift between successive layers decrease, whereas its am plitude increases. On the other hand, all tensile layers develop short-wave length localized symmetrical thickness variations often involving facets. F or intermediate misorientations, they also display undulations similar to t hose observed in compressive layers. (C) 2000 American Institute of Physics . [S0003-6951(00)00603-3].