Exploring semiconductor quantum dots and wires by high resolution electron microscopy (original) (raw)
Related papers
2002
Transmission electron microscopy studies in both the scanning and parallel illumination mode on samples of two generic types of self-assembled semiconductor quantum dots are reported. III-V and II-VI quantum dots as grown in the Stranski-Krastanow mode are typically alloyed and compressively strained to a few %, possess a more or less random distribution of the cations and/or anions over their respective sublattices, and have a spatially non-uniform chemical composition distribution. Sn quantum dots in Si as grown by temperature and growth rate modulated molecular beam epitaxy by means of two mechanisms possess the diamond structure and are compressively strained to the order of magnitude 10 %. These lattice mismatch strains are believed to trigger atomic rearrangements inside quantum dots of both generic types when they are stored at room temperature over time periods of a few years. The atomic rearrangements seem to result in long-range atomic order, phase separation, or phase transformations. While the results suggest that some semiconductor quantum dots may be structurally unstable and that devices based on them may fail over time, triggering and controlling structural transformations in self-assembled semiconductor quantum dots may also offer an opportunity of creating atomic arrangements that nature does not otherwise provide.
Self-organized semiconductor nanostructures: shape, strain and composition
Materials Science and Engineering: C, 2002
An overview on various X-ray scattering and diffraction techniques is presented, from which information on the shape and size of quantum dots and wires, their composition and strain state can be obtained. These methods are described and applied to studies of InAs, PbSe and Ge-based nanostructures.
Applied Physics Letters, 2004
The model systems for self-organized quantum dots formed from elemental and compound semiconductors, namely Ge grown on Si(001) and InAs on GaAs(001), are comparatively studied by scanning tunneling microscopy. It is shown that in both material combinations only two welldefined families of faceted and defect-free nanocrystals exist (and coexist). These three-dimensional islands, pyramids and domes, show common morphological characteristics, independently of the specific material system. Universal behavior is also observed in the capping-passivation process that turns the nanocrystals in true quantum dots.
Analysis of the 3D distribution of self-assembled stacked quantum dots by electron tomography
2012
This paper has been withdrawn by the authors. The 3D distribution of self-assembled stacked quantum dots (QDs) is a key parameter to obtain the highest performance in a variety of optoelectronic devices. In this work, we have measured this distribution in 3D using a combined procedure of needle-shape specimen preparation and electron tomography. We show that conventional 2D measurements of the distribution of QDs are not reliable, and only a 3D analysis allows an accurate correlation between the growth design and the structural characteristics.
Analysis of the 3D distribution of stacked selfassembled quantum dots by electron tomography
2012
The 3D distribution of self-assembled stacked quantum dots (QDs) is a key parameter to obtain the highest performance in a variety of optoelectronic devices. In this work, we have measured this distribution in 3D using a combined procedure of needle-shaped specimen preparation and electron tomography. We show that conventional 2D measurements of the distribution of QDs are not reliable, and only 3D analysis allows an accurate correlation between the growth design and the structural characteristics.
Physical Review B, 1998
High-resolution electron microscopy, on-zone bright-field imaging, and image simulation were used to investigate the shape of capped In 0.6 Ga 0.4 As/GaAs semiconductor quantum dots. Cross-section ͗110͘ highresolution images suggest that the quantum dots are lens shaped, while the ͓001͔ on-zone bright-field images show a contrast that suggests a quantum dot morphology with four edges parallel to ͗100͘. The image simulation, however, suggests that a spherical quantum dot can produce a square-shaped image. These observations lead to the conclusion that the quantum dots in buried In 0.6 Ga 0.4 As/GaAs semiconductor heterostructures are lens shaped. ͓S0163-1829͑98͒51432-4͔