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HL: Halbleiterphysik

HL 31: Quantenpunkte und -dr
ähte: Herstellung und Charakterisierung

HL 31.3: Vortrag

Mittwoch, 26. März 2003, 15:00–15:15, BEY/154

STM analysis of the growth and overgrowth of ”large” InAs/GaAs(001) quantum dots — •Giovanni Costantini, Carlos Manzano, Rudeesun Songmuang, Oliver Schmidt, and Klaus Kern — Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany

InAs/GaAs(001) quantum dots (QDs) are grown at high temperature and extremely low flux and analyzed by in-situ scanning tunneling microscopy. A bimodal distribution of dots is measured, composed by ”small” and ”large” islands. While the former show a broad distribution of sizes and shapes, the latter appear to be highly uniform and have a truncated-pyramid shape with irregular octagonal base. (110) and (111) facets are identified and atomically resolved, showing respectively (1x1) and (2x2) surface reconstructions. The experimental findings are in excellent agreement with recent theoretical predictions of the equilibrium crystal shape, demonstrating that the chosen deposition conditions are close to thermodynamic equilibrium. The low-temperature GaAs overgrowth of these QDs is investigated during the initial stages (1-30 ML). Two regimes appear to dominate the capping, an initial partial dissolution of the QDs followed by a true overgrowth. The quantitative analysis of these regimes reveals two competing processes and allows the development of a simple quantitative model for the dot dissolution. An atomistic interpretation of the observed phenomena is also presented, demonstrating that kinetic effects are fundamental for all the stages of the capping process.