HREM of epitaxial layers in the InAs/GaAs system

Abstract

(110) and (100) cross sectional HREM of the multilayered InAs/GaAs(001) heterosystem grown by MBE was carried out using digital filtering and image simulation. Two types of specimens were investigated: strained layer superlattices (SLS) with pseudomorphic layers ( h = 0.6−0.9 nm), and specimens with varying InAs layer thickness. It was shown that at h = 0.6−0.9 nm InAs layers are pseudomorphic; the InAs lattice is tetragonally distorbed. Further increase of layer thickness results in transformation of the continuous layer into an island one. At initial stages of island formation, when first single misfit dislocations (MDs) are introduced, tetragonal distortions may also be observed. At later stages lattice mismatch is compensated by 60° MDs. With further increase of InAs layer thickness ( h > 10 nm) the island layer is transformed into a continuous one. Mismatch is compensated by Lomer dislocations and by pairs of 60° dislocations on the interface.