TEM study of the morphological and compositional instabilities of InGaAsP epitaxial structures

We first study by transmission electron microscopy how the morphological in stability of misfitting epitaxial layers depends on the misorientation of t he substrate and sign of the misfit. In superlattices containing alternatin g strained and lattice-matched layers, the surface non-planarity develops b y bunching of a large fraction of the original substrates steps for layers under compression, whereas for layers under tension new steps are created. In order to investigate the initial stages of step-bunching and its evoluti on during growth, we also fabricated homogeneously stressed structures wher e marker layers were incorporated. Step-bunching is already present after d eposition of a few nanometers of material. However, its development does no t appear regular during growth. After a first phase where the amplitude of the step bunches increases. we observe its stabilisation and then its decre ase. The final part of the paper is dedicated to the study of coupled morph ological and compositional instabilities in thick quaternary alloy layers n early lattice-matched to their substrate. We use X-ray microanalysis to qua ntify the variations of composition which are coupled with their surface no n-planarities. (C) 2000 Elsevier Science B.V. All rights reserved.