We have revealed the origin of typical extended defects in semiconductor heterostructures with heterovalent interfaces, namely pairs of stacking faults in pseudomorphic ZnSe epitaxial layers grown on a GaAs(001) substrate. We have taken structural images of the defects by means of high-resolution transmission electron microscopy. Analyzing the images combined with first-principles energy calculations, we have clarified the atomistic structure of the extended defects: An intrinsic stacking fault on (111) intersects the other one on (11)
on the interface between the epitaxial layer and the substrate, forming an intersecting line along .
Around the intersecting line, we have found that Ga, As, and Se atoms form the specific reconstructed structure with relatively low formation energy, which corresponds well to a reconstructed surface structure on GaAs(001) with excess As and additional Se atoms. We have therefore attributed the stability of extended defects to the reconstructed surface structure on the substrate formed before epitaxial growth. © 2003 American Institute of Physics.