Step-bunching instability in strained-layer superlattices grown on vicinal substrates

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Abstract
Epitaxial structures containing either compressive or tensile InGaAsP layers 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 asymmetrical lateral thickness modulations. We demonstrate that the associated surface undulation consists of periodic bunches involving only the initial substrate steps. With increasing misorientation, the wavelength of the modulation and its phase shift between successive layers decrease, whereas its amplitude increases. On the other hand, all tensile layers develop short-wavelength localized symmetrical thickness variations often involving facets. For intermediate misorientations, they also display undulations similar to those observed in compressive layers.