Kinetic Monte Carlo simulations and cross-sectional scanning tunneling microscopy as tools to investigate the heteroepitaxial capping of self-assembled quantum dots

Abstract

The growth of self-assembled quantum dots has been intensively studied in the last decade. Despite substantial efforts, a number of details of the growth process remain unknown. The reason is the inability of current characterization techniques to image the growth process in real time. In the current work this limitation is alleviated by the use of kinetic Monte-Carlo simulations in conjunction with cross-sectional scanning tunneling microscopy. The two techniques are used to study the method of strain engineering as a procedure to control the height of quantum dots. We show for the first time that fully three-dimensional kinetic Monte-Carlo simulations can be matched with the experimentally obtained morphology of buried quantum dots and that combination of the two techniques provides details of the growth process that hitherto could not be obtained.

Height control of self-assembled quantum dots by strain engineering during capping

“…There is a qualitative agreement between the trend observed from the experimental data (red open symbols) and the results of the simulation (black filled symbols) which confirms that a smaller mismatch between QD and capping layer will reduce the dot erosion process 15 and will result in QDs with a larger height. In The qualitative agreement with the trend found for the systems studied in this letter and the points obtained for different InAs QDs systems is striking, in spite of the differences between the systems considered (i.e., different capping and different morphology of the uncapped QDs).This suggests that the morphological properties of uncapped QDs are of secondary importance with respect to the misfit between the QD and the capping layer material.…”

“…For the other parameters, we take c GaÀGa ¼ 0:2506; c GaÀIn ¼ 0:2217, and c InÀIn ¼ 0:2169 all in eV. 15 The elastic energy DW is the change in the total elastic energy given by the removal of the atom considered. The elastic interactions in the system are calculated with a ball and spring model, using two spring constants, k L and k D , and the misfit l between InAs and GaAs.…”

“…14 The effects on the QDs morphology are studied, and the results obtained from the simulation are compared with cross-sectional Scanning Tunnel Microscopy (X-STM) measurement on QD samples grown by Molecular Beam Epitaxy (MBE). 15 In our KMC model for hetero-epitaxial growth every pair of III-V atoms in the system is modeled with a cube, as shown in Fig. 1.…”

Kinetic Monte Carlo simulation of heteroepitaxial growth: Wetting layers, quantum dots, capping, and nanorings

“…It is interesting to note that the dot material (yellow colored atoms) is intermixed with the capping material except for a ring-shaped region immediately near the edge of the dot. This behavior has been reported in experiments [49].…”

“…In closing, we mention that surface decomposition KMC has recently been applied to study capping of GaAs dots by Ga 1−x In x As [49]. In that paper the reader will find detailed comparisons of simulations using the algorithm presented here with experimental results.…”