TEM evaluation of defects in GaAs/InAs 3D-layer/GaAs heterostructures grown by molecular beam epitaxy

Defects generated in GaAs/InAs three-dimensional layer/GaAs heterostructures grown on (001)GaAs substrates by molecular beam epitaxy have been systematically evaluated by transmission electron microscopy. The crystal growth of InAs on GaAs is subject to Stranski-Krastanow mode, that is, two-dimensional growth up to 1 monolayer coverage, then three dimensional growth. During the growth of 1 to 2.5 monolayers of InAs, the density of islands linearly increases with growth coverage while their diameter remains constant. When the coverage of InAs exceeds 2.5 monolayers, large islands are often formed by coalescence of two islands. Three types of defects are observed: V-shaped dislocations consisting of two dissociated dislocation pairs, multiple intrinsic stacking faults lying on one to four equivalent {III}planes and dislocation loops. All of these defects originate from the large islands. Based on a detailed characterization of these defects, possible generation mechanisms are discussed