AVS 52nd International Symposium
    Electronic Materials and Processing Thursday Sessions
       Session EM2-ThM

Paper EM2-ThM4
Control of InAs/GaAs Quantum Dot Density and Positioning Using Modified Buffer Layers

Thursday, November 3, 2005, 9:20 am, Room 310

Session: Heteroepitaxy and Low-Dimensional Structures
Presenter: W. Ye, The University of Michigan
Authors: W. Ye, The University of Michigan
S. Hanson, The University of Michigan
M. Reason, The University of Michigan
X. Weng, The University of Michigan
R.S. Goldman, The University of Michigan
Correspondent: Click to Email
Recently, strain-induced self-assembled quantum dots (QDs) have enabled the development of high performance light-emitters and detectors. Further advances in optoelectronics and quantum computing will require a narrowing of the density of states and achievement of periodic charge distributions, both of which necessitate the fabrication of high density, nearly monodispersed, highly ordered QD arrays. Various efforts have been made to achieve high densities of laterally ordered InAs/GaAs QDs. However, the mechanisms of lateral ordering of QDs are the subject of continued debate. A significant remaining question concerns the effects of buffer layers on the QD density and lateral ordering. Therefore, we have examined the patterning effects of buffer layers during the growth of QD SLs. Our QD SLs consisted of 2.6 ML InAs and 5 nm GaAs grown by molecular beam epitaxy at 500°C. Prior to QD deposition, GaAs buffer layers were grown under several different conditions, involving growth and/or annealing at 580°C and 500°C. High temperature grown buffers consist of relatively flat surfaces, while lower temperature grown buffers contain "mound-like" features elongated along the [1-10] direction. Isotropic distributions of QDs are observed for QD growth on flat buffers. Interestingly, QD alignment along the [1-10] direction is observed for QD SL growth on buffers containing mounds. This anisotropic QD alignment is enhanced as the number of QD SL increases and is dependent on the density of mounds. For flat buffers, the density of QDs decreases with stacking, consistent with the model of Tersoff. However, for buffers containing mounds, this effect is compensated by an increase in QD density. We propose a new mechanism for QD nucleation, which is based upon patterning by undulated In-enriched GaAs spacer layers following the initials sets of QD SLs.