Effect of overgrowth on shape, composition, and strain of SiGe islands on Si(001)

Abstract

We present a method and results based on x-ray scattering capable of resolving the shape and strain distribution in buried islands, as well as their vertical composition gradient. As an example, results are presented obtained for a single layer of SiGe dome-shaped islands capped by a 160-nm Si layer. For a growth temperature of 700°C, a significant decrease of the average Ge content from about xϭ0.78 before overgrowth to about xϭ0.37 is found. The diameter of the islands increases from 110 to about 180 nm, their height shrinks from about 13 nm to 6 nm. This significant change of the island shape and content is accompanied by a pronounced change of their average in-plane lattice constant. The strain status of the overgrown flat islands is close to that of an embedded SiGe quantum well, i.e., with respect to the relaxation status of the uncapped islands a considerable strain redistribution takes place.

Beyond the ensemble average: X-ray microdiffraction analysis of single SiGe islands

“…Thus, by keeping the reciprocal space position fixed, an intensity modulation is observed while translating the sample in real space. 27 As previously shown for ensembles, 28 also buried islands produce enough distinct scattering patterns to be analyzed by the presented method.…”

Analysis of strain and intermixing in single-layerGe∕Siquantum dots using polarized Raman spectroscopy

“…On the other hand, a highly anisotropic lateral Ge profile was found by a selective etching technique in uncapped Ge/ Si pyramids and explained by a model of intermixing caused by surface diffusion. 7 X-ray diffraction ͑XRD͒ data on buried 8 and uncapped 9 Ge/ Si dots, selective etching of stacked dot layers, 10 and micro-Raman data on Ge/ Si dots 4 and thinlayer heterostructures exhibit significant z anisotropy of the Ge content due to intermixing. Overgrowth of dots by a Si layer is usually required in these structures.…”

X-ray diffraction investigation of a three-dimensional Si/SiGe quantum dot crystal

“…Assuming rotational symmetry instead of a quadratic one actually has no big influence on the obtained results as long as only one azimuth is concerned. 53 Only if both ͓100͔ and ͓110͔ azimuths are fitted simultaneously, the difference in the aspect ratios has to be taken into account. The dots in the first layer, grown within the pits of the prepattern, have different shapes-from the TEM image in Fig.…”