Münster 1999 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 17: Quantenpunkte und Quantendr
ähte II
HL 17.7: Vortrag
Dienstag, 23. März 1999, 12:00–12:15, H4
Electron microscope structure investigation of quantum dots: Molecular dynamics and image simulations — •Scheerschmidt Kurt1, Werner Peter1, and Grundmann Marius2 — 1Max-Planck-Institut f"ur Mikrostrukturphysik, Halle — 2Institut f"ur Festk"orperphysik, Technische Universit"at Berlin
The structural properties of nm-scale objects as, e.g., quantum dots (QD’s), influence strongly the electronic pro-perties of novel semiconducting materials/1/. Electron microscope investigations using both the high resolution (HREM) and the conventional transmission diffraction contrast (TEM) techniques enable to study geometry, size, shape, etc. of QD’s. However, the visualization and the unique interpretation of the images is rather complicated for coherently strained nm-scale islands owing to the high strain level around the QD’s. TEM and HREM contrast simulations based on empirical molecular dynamics structure modelling have been applied to quantify the imaging of coherently strained nm-scale InAs islands embedded in a GaAs matrix /2/. The HREM contrast of QD’s is shown to be rather sensitive to both foil thickness and defoci, whereas the symmetrical zone-axis BF contrast with lower resolution is mainly determined by the sample thickness, the depth of the QD in the sample, and the strains created by the QD in the matrix. Optimum HREM imaging conditions are found to reveal the different shapes uniquely and to measure the size of QD’s. To provide a quantitative comparison with experimental images the models have to be refined by using more realistic interaction potentials to include, e.g., diffusion and reordering processes. /1/ M. Grundmann, et al., Laser and Optoelektronik, 30 (1998) 70. /2/ S.Rouvimov, K. Scheerschmidt, phys. stat. sol (a) 150 (1995) 471.