Size-Dependent Strain Relaxation in InAs Quantum Dots on Top of GaAs(111)A Nanopillars

Abstract

The size-dependent strain relaxation in InAs quantum dots on the top face of GaAs(111)A nanopillars is studied experimentally by scanning transmission electron microscopy (STEM) and theoretically using molecular static simulations. In the experiment, a dislocation-free, coherent state is observed for InAs dimensions below 10 nm in width and 7 nm in height, while 60° misfit dislocations occur for larger sizes. Experimental strain maps reveal the presence of a narrow-strained region at the heterointerface with a 20–80% width of 1.2 nm in the coherent case and 0.4 nm in the dislocated state, in agreement with simulations. Moreover, an analysis of the amount of misfit relaxed by the observed dislocations shows that the transition between the purely elastic and plastic relaxation regimes appears to be gradual. Intensity profiles of STEM images reveal that the misfit dislocations are located directly at the GaAs/InAs heterointerface.