Asymmetries in dislocation densities, surface morphology, and strain of GalnAs/GaAs single heterolayers

The dislocation densities, surface morphology, and strain of Gal _ x In" As/GaAs epitaxial interfaces as a function of indium composition and layer thickness have been investigated by transmission electron microscopy, medium energy ion blocking, and double-crystal x-ray diffractometry. The electron microscopy shows that in the thinnest dislocated films (90 and 160 nm, x = 0.07) 60· a dislocations form first in one (110) direction at the interface. Surprisingly, however, an asymmetry in residual layer strain is not detected in these samples, suggesting that the dislocations have the same Burgers vector or are evenly distributed between two Burgers vectors. Orthogonal arrays of dislocations are observed in films thicker than 300 nm (60" and edge-type, x = 0.07). In this case, dislocation densities in each OW) direction are equal to within experimental error while an asymmetry in in-plane strain is measured (18% and 30% for x = 0.07,300, and 580 nm thick, respectively). An unequal distribution of Burgers vectors of 60· or edge-type dislocations is considered responsible for the strain asymmetry in these thicker samples.