Evolution of crystalline domain size and epitaxial orientation of CdTe/Si(111) quantum dots

We have investigated the crystalline configuration of CdTe quantum dots (QDs) grown on hydrogen passivated Si(111) substrates by hot wall epitaxy. Coplanar and grazing incidence diffraction were used for determination of dot strain state and the vertical and lateral dimensions of the crystalline domain. A change in aspect ratio was observed as a function of dot size. X-ray diffraction (XRD) results show that despite a mismatch of almost 20% the islands grow with a fairly good epitaxial orientation with respect to the Si(111) substrate. The dot mosaicity was also determined and was found to decrease with island size from 7° to about 4° for the samples studied, indicating an improvement in epitaxial quality even before the island coalescence. Careful observation of CdTe ( 2 2 ¯ 0 ) reflections in an azimuthal scan showed that an additional ensemble of islands is responsible for low-intensity peaks with a 30° symmetry besides the expected 60° symmetry. Transmission electron microscopy results have shown good accordance with atomic force microscopy and XRD and revealed the presence of an amorphous Tellurium rich oxide layer at the CdTe/Si interface, which could explain the fully unstrained QD state observed.