A simple critical thickness for generating lattice misfits was insufficient to describe the onset strain relaxation in InAs quantum dots. A predominant dot family was shown to relieve its strain by In/Ga interdiffusion, rather than by lattice misfit, at the onset of strain relaxation. This argument was based upon photoluminescence spectra, which showed the emergence of a fine blue-shifted transition at the onset of strain relaxation, along with a low-energy transition from a dot family degraded by lattice misfits. From the analysis of the temperature-dependent blue-shift and energy separation between the ground and excited-state transitions, the blue-shift was attributed to In/Ga interdiffusion. Transmission electron microscopy suggested a relaxation-induced indium migration from the interdiffused dot family to the dislocated dot family. Post-growth thermal annealing could further relieve strain by inducing more In/Ga interdiffusion in the interdiffused dot family and more dislocations in the dislocated dot family. This study explains the co-existence of strong carrier confinement in the quantum dots and enormous misfit-related traps in the capacitance-voltage spectra, and an elongated quantum dot electron-emission time.

How Do InAs Quantum Dots Relax when the InAs Growth Thickness Exceeds the Dislocation-Induced Critical Thickness? J.F.Chen, Y.C.Lin, C.H.Chiang, R.C.C.Chen, Y.F.Chen, Y.H.Wu, L.Chang: Journal of Applied Physics, 2012, 111[1], 013709