Spontaneous lateral composition modulation in InAlAs and InGaAs short-period superlattices

The microstructure of spontaneous lateral composition modulation along the [1 1 0] direction has been studied in (InAs)(n)/(AlAs)(m) short-period superlattices grown by molecular beam epitaxy on (0 0 1) InP. X-ray diffraction and transmission electron microscopy show that global strain (epsilon) in the superlattice reduces the degree of composition modulation, which disappears for /epsilon/ > 0.7%. For tensile strains of epsilon approximate to + 0.4%, we find that In-rich columns become regularly spaced and correlated with cusps in the growth surface. A similar correlation is seen in (InAs)(n)/(GaAs)(m) short-period superlattices between the enriched columns and the peaks and valleys of {1 1 4}(A) facets on the surface. The enriched columns in the (InAs)(n)/(GaAs)(m) layer land the facets) extend for much longer distances(similar to 0.2-0.4 mu m) in the [1 (1) over bar 0] direction than do the columns in the (InAs)(n)/(AlAs)(m) layer (similar to 56 nm). (C) 1998 Elsevier Science B.V. All rights reserved.