THREADING DISLOCATIONS IN MULTILAYER STRUCTURE OF INAS SELF-ASSEMBLEDQUANTUM DOTS

A multilayer structure consisting of 20 layers of InAs self-assembled quantum dots was grown by molecular beam epitaxy and observed by trans mission electron microscopy. The positions of quantum dots in a quantu m-dot layer were not correlated with those in the lower quantum-dot la yer because of the thick (70nm) GaAs spacer layer. Threading dislocati ons were observed, which originated from large strain-relaxed (incoher ent) InAs islands in a, quantum-dot layer. The dislocations were 30 de grees dislocations in the [1 (1) over bar 2] and [(1) over bar 12] dir ections, and were generated by a misfit between large InAs islands and a GaAs overlayer.