The atomistic structure and electrical properties of a symmetrical 5.4° [001] tilt grain boundary in Fe‐doped SrTiO3 have been investigated, respectively, by means of various transmission electron microscopy (TEM) techniques and impedance spectroscopy. In weak‐beam dark‐field images, the grain boundary is revealed to consist of a periodic array of dislocations; high‐resolution TEM images show that the dislocation cores are separated by regions of strained lattice. The impedance response of the bicrystal has been measured in the frequency range 20 Hz ≤f≤ 106 Hz as a function of temperature and oxygen partial pressure. The transport of charge across the array of dislocations that form the grain boundary is strongly hindered. Analysis of the impedance data in terms of a double‐Schottky‐barrier model yields a space‐charge potential that exhibits a weak dependence on temperature and oxygen partial pressure and is ∼0.55 V in the investigated regime.

In a stack of vertically aligned Stranski–Krastanov grown islands, the critical thickness for planar growth for all but the initial dot layer is reduced, if the thickness of the spacer layer ts is smaller than a certain value t0. We present structural and photoluminescence results on the basis of the extensively studied lattice-mismatched material system Si/Ge.

A very small amount of pre-deposited C on a Si substrate causes island formation after epitaxial growth of less than 2 monolayers Ge. These C-induced Ge dots can be as small as 10 nm in lateral size and 1 nm in height. Their areal density is 1011 cm−2. Intense photoluminescence signal from these small Ge quantum dots is observed reaching a maximum for 2.1±0.3 monolayers of Ge. In the initial stages of island formation, the optical transition of the wetting layer is blue-shifted by strain compensation effects. We propose spatially indirect mechanisms of radiative recombination between electrons confined in the underlying wetting layer and holes confined in the Ge islands.

We report on experiments aiming to produce Ge quantum dots embedded in Si. Employing cross-sectional transmission electron microscopy, we have studied the misfit stress-induced self-alignment of islands belonging to consecutive Stranski–Krastanov layers of Ge buried in Si by molecular beam epitaxy. Quantitative evaluation of the micrographs has revealed the critical Si interlayer thickness below which the island positions in successive Ge layers begin to correlate. Moreover, we have quantitatively analyzed the influence of the Si interlayer thickness on the coarsening of the Ge islands from one buried Ge layer to the next.