New relaxation mechanisms in InGaAs/GaAs (111) multiple quantum well

A study by planar view transmission electron microscopy (PVTEM) of crystall ine defect types in InGaAs/GaAs MQW grown on GaAs(111)B substrates is prese nted. The In-content of InxGa1-xAs layers was increased from x = 0.1 to 0.3 . The relaxation in structures with low In-content (x < 0.2) occurred mainl y through the formation of a triangular network of misfit dislocations (MDs ) along each one of the three [<1(1)over bar>0] directions contained in the interface. However, for In-contents above 22%, a new configuration of MDs as three-pointed starshaped is observed. These star dislocations were forme d by arms parallels to the [11(2) over bar] directions contained in the gro wth plane. The interaction between two or more star dislocations worked as a new dislocation multiplication source. These new star dislocations often changed their dislocation lines turning towards the usual [<1(1)over bar>0] directions. The characterization of this new dislocation configuration dem onstrated that its Burgers vector lay on the growth plane with a strain-rel ieving component larger than the habitually considered. This result may mod ify the expectatives of a larger critical layer thickness for InGaAs/GaAs(1 11)B heterostructures with high In-content. (C) 1999 Elsevier Science Ltd. All rights reserved.