AVS 50th International Symposium
    Semiconductors Friday Sessions
       Session SC+NS-FrM

Paper SC+NS-FrM5
Anisotropic Stress Relaxation and Ordering of InAs/GaAs Quantum Dot Superlattices

Friday, November 7, 2003, 9:40 am, Room 321/322

Session: Low Dimensional Structures and Amorphous Silicon
Presenter: W. Ye, The University of Michigan
Authors: W. Ye, 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, self-assembled quantum dot (QD) superlattices (SLs) have shown significant promise for a wide range of electronic and optoelectronic device applications. In general, self-assembled QD formation is driven by the elastic relaxation of stress via island nucleation. The vertical stacking of QDs is often explained by the preferred nucleation of islands at strain energy minima directly above buried dots. However, the mechanisms of lateral ordering of QD arrays are the subject of continued debate. For example, anisotropic lateral alignment of QDs has been observed in a number of materials systems. A significant remaining question concerns the relative effects of buffer layer patterning and anisotropic stress relaxation on this lateral QD alignment. Therefore, we have examined the patterning effects of buffer layers, as well as the stress relaxation process during the growth of stacked QDs. 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 at 580°C and/or 500°C. During QD growth, reflection high energy electron diffraction (RHEED) reveals a streaky to spotty pattern transformation, typical of the Stranski-Krastanov (S-K) growth mode transition. However, simultaneous wafer curvature measurements using multi-beam optical stress sensor (MOSS) reveal that stress relaxation occurs after the S-K growth mode transition is complete. Ex-situ atomic force microscopy measurements indicate a preferential alignment of QDs along the [-110] direction. This anisotropic alignment is enhanced as the number of SL periods increases and may be due to pre-patterning by the 500°C buffer layer. We will discuss the relative roles of buffer layer patterning and anisotropic stress relaxation on QD ordering. This work was supported in part by DOE (Photovoltaics Beyond the Horizon Program), ARO (MURI Program), and NSF (Nanoscale Exploratory Research Program).