Formation and stacked layer of quantum dots

Abstract

Three-dimensional formation occurring at the initial stage of the heteroepitaxial growth of a lattice-mismatched system is reviewed. It is experimentally proved that the formation of InAs islands on the GaAs substrate is due to the Stranski–Krastanov (S–K) growth mode. This formation has been proposed to realize a mesoscopic island structure which can be utilized as a quantum dot (QD). They are naturally formed with the S–K growth mode. They have been called naturally- or self-formed QDs. The strain energy of the QD is calculated with the valence-force field model, and then the possible formation of dislocation-free QDs is described. The experimental results of InAs/GaAs and InP/GaP QDs are presented. In the stacked layer of InAs/GaAs QDs, the GaAs spacer thickness for the vertical ordering of QDs is investigated. The ordering, dependent on the spacer thickness, is found by the transmission electron microscope images of cross-sectional stacked layers. The QD can be neither stacked nor vertically ordered when the thickness is greater than 2 h where h denotes the QD height. The QDs are crushed when the spacer is thinner than h. The vertically ordered QDs are stacked when the GaAs spacer thickness is between h and 2 h.