We study the interplay of elastic and plastic strain relaxation of SiGe/Si(001). We show that the formation of crosshatch patterns is the result of a strain relaxation process that essentially consists of four subsequent stages: (i) elastic strain relaxation by surface ripple formation; (ii) nucleation of dislocations at the rim of the substrate followed by dislocation glide and deposition of a misfit dislocation at the interface; (iii) a locally enhanced growth rate at the strain relaxed surface above the misfit dislocations that results in ridge formation. These ridges then form a crosshatch pattern that relax strain elastically. (iv) Preferred nucleation and multiplication of dislocations in the troughs of the crosshatch pattern due to strain concentration. The preferred formation of dislocations again results in locally enhanced growth rates in the trough and thus leads to smoothing of the growth surface.

We show how optical phonons can be used as efficient probes in self-organized Si1−xGex islands grown on Si(001). Both the alloy composition and residual strain in the islands were originally determined from the phonon frequencies and Raman intensities. The experimental results are in good agreement with the strain relaxation simulated by means of the finite element method.

We investigated the composition-dependent size of pseudomorphic Si1−xGex islands on Si(001). Si1−xGex layers with 0.05⩽x⩽0.54 were deposited from metallic solution. The island growth occurs near thermodynamic equilibrium and facilitates a comparison of the results with predictions based on energetics. We find pseudomorphic islands with base widths ranging from several μm to a few nm. We show that it is possible to adjust the island size by simply choosing the appropriate layer composition. Varying deposition temperatures and growth velocities do not affect the scaling behavior.

We analyse by means of transmission electron microscopy (TEM) and atomic force microscopy (AFM) the strain relaxation mechanisms in InGaN layers on GaN as dependent on the In content. At the experimentally given thickness of 100 nm, the layers remain coherently strained, up to an In concentration of 14 %. We show that part of the strain is reduced elastically by formation of hexagonally facetted pinholes. First misfit dislocations are observed to form at pinholes that reach the InGaN/GaN interface. We discuss these results in the framework of the Matthews-Blakeslee model for the critical thickness considering the Peierls force for glide of threading dislocations in the different slip systems of the wurtzite lattice.

Silicon carbide, a potentially powerful device material, suffers from microscopic hollow defects called micropipes. Their nature is not satisfactorily clarified yet. Our analysis shows that they are hollow core dislocations according to Frank's model, but contain dislocations of mixed type.[S0031-9007 (97)05011-4] PACS numbers: 61.72.Bb, 61.16.Ch, 61.72.Ff, 61.72.LkMicropipes are hollow tubes penetrating SiC single crystals along their growth direction ([1], for review see, e.g., [2]) and occur very frequently in SiC. They can be interpreted in the framework of Frank's model of a hollow core dislocation [3,4]: When the magnitude of the Burgers vector of a dislocation exceeds a critical value (approximately 1 nm) it is energetically more favorable to remove the highly strained material around the dislocation line and to create an additional free surface in the shape of a tube. The relation between the equilibrium radius r 0 and the length of the Burgers vector B in the micropipe is given by Frank's formula,(1) m: shear modulus (for SiC: m 1.9 3 10 11 J͞m 3 ); g: surface energy of the inner surface of the micropipe. We will use this surface energy as a fit parameter in the following discussion. We have to note here that Frank's model is applicable to any type of dislocation. However, in the past, because of the easy accessibility, only screw components were considered [4-6] and the obtained results were consequently discussed in terms of "screw dislocations." In the following discussion we will first adopt this notion and present our results in this familiar picture, but later we must modify it by considering an additional edge component of the Burgers vector. In this case, the shear modulus m in Eq. (1) has to be replaced by the appropriate energy factor K we take for Poisson's ratio y 0.16 [7].In former papers [4,5] we investigated by atomic force microscopy (AFM) growth spirals with micropipes in