Growth mode of tensile-strained Ge quantum dots on different III–V buffers by molecular beam epitaxy is studied by a combination of reflection high-energy electron diffraction, atomic force microscopy and transmission electron microscopy. The Ge-QDs growth on the InAlAs buffer lattice matched to InP and on InAs buffer on GaSb follows the Volmer–Weber growth mode with round Ge QDs and no Ge wetting layer, while it obeys the Stranski–Krastanov growth mode on GaSb, AlSb and AlGaSb on GaSb substrates, showing rectangular shaped platelets and a clear Ge wetting layer. The discovery of the Volmer–Weber growth mode is essential to avoid forming a wetting layer and the subsequent antiphase-domain defects when capping III–Vs on Ge-QDs, important for potential optoelectronic applications.

GeSn alloy with 7.68% Sn concentration grown by molecular beam epitaxy has been rapidly annealed at different temperatures from 300°C to 800°C. Surface morphology and roughness annealed below or equal to 500°C for 1 min have no obvious changes, while the strain relaxation rate increasing. When the annealing temperature is above or equal to 600°C, significant changes occur in surface morphology and roughness, and Sn precipitation is observed at 700°C. The structural properties are analyzed by reciprocal space mapping in the symmetric (004) and asymmetric (224) planes by high resolution X-ray diffraction. The lateral correlation length and the mosaic spread are extracted for the epi-layer peaks in the asymmetric (224) diffraction. The most suitable annealing temperature to improve both the GeSn lattice quality and relaxation rate is about 500°C.