RELAXATION MECHANISM OF INGAAS SINGLE AND GRADED LAYERS GROWN ON (111)B GAAS

In this work we study the influence of the composition (strain) and th e layer thickness of InGaAs grown on (111)B GaAs substrates on the sur face morphology and defect distribution (strain relief). Samples of un iform (x = 0.13 or 0.22) and graded (x(initial) = 0.10 for each sample ; x(final) = 0.17 and 0.25) composition have been studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). The relaxation mechanism f or the two series of samples is the same. SEM observations reveal a su rface roughness with a triangular structure, where the 'cross-hatch pa ttern' distribution is more isotropic and homogeneous as the thickness and In composition increase. Misfit dislocations and deformation twin s (band twins), anisotropically and inhomogeneously arranged, are obse rved in all the studied samples. Deformation twins are formed by the n ucleation of partial dislocations from the film surface. A mechanism o f the observed band twins formation is proposed. (C) 1998 Elsevier Sci ence S.A.