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

A study by planar view transmission electron microscopy (PVTEM) of crystalline defect types in InGaAs/GaAs MQW grown on GaAs(111)B substrates is presented. 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 mainly 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 formed by arms parallels to the [11(2) over bar] directions contained in the growth 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 demonstrated that its Burgers vector lay on the growth plane with a strain-relieving component larger than the habitually considered. This result may modify the expectatives of a larger critical layer thickness for InGaAs/GaAs(111)B heterostructures with high In-content. (C) 1999 Elsevier Science Ltd. All rights reserved.