EFFECTS OF GAAS-SPACER STRAIN ON VERTICAL ORDERING OF STACKED INAS QUANTUM DOTS IN A GAAS MATRIX

Vertical ordering in stacked layers of InAs/GaAs quantum dots is curre ntly the focus of scientific research because of its potential for opt oelectronics applications. Transmission electron microscopy was applie d to study InAs/GaAs stacked layers grown by molecular-beam-epitaxy wi th various thicknesses of GaAs spacer. Thickness dependencies of quant um dot size and their ordering were observed experimentally and, then, compared with the results of strain calculations based on the finite element method. The vertical ordering did occur when the thickness of the GaAs spacer was comparable with the dot height. The ordering was f ound to be associated with relatively large InAs dots on the first lay er. Quantum dots tend to become larger in size and more regular in pla ne with increasing numbers of stacks. Our results suggest that the ver tical ordering is not only affected by strain from the InAs dots on th e lower layer, but by total strain configuration in the multi-stacked structure.