Scanning transmission electron microscopy (STEM) study of InAs/GaAs quantum dots

Scanning transmission electron microscopy (STEM) and energy dispersive X-ray analysis (EDX) have been used to investigate the size and composition of InAs/GaAs quantum dot (QDs). It is shown that the QD exist within the wetting layer and not on it. In QD bilayers where the dots are uncorrelated along the growth direction a comparison of the indium EDX signals from the wetting layer (WL) and a dot allow us to estimate the compositions of these regions as In0.07Ga0.93As and In0.31Ga0.69As respectively. We have used the STEM technique to investigate the effects of annealing QDs in order to modify the emission energy. EDX measurements show that the dots increase in size by a factor of 2 for the longest anneals and there is a concomitant decrease in the indium concentration resulting in blue shifts up to 300 meV and a narrowing of the linewidth to ∼12 meV