Single phase Si1−xGex nanocrystals and the shifting of the E1 direct energy transition

We report preparation and characterization of Si1−xGex alloys with varied composition x of a large range from 0-1. The materials have been obtained by co-sputtering, followed by a heat treatment process at 600, 800, and 1000 °C for 30 min in a nitrogen gas atmosphere. X-ray diffraction data have revealed the formation of single-phase nanoparticles in the face-centered cubic (FCC) structure of Si1−xGex alloys. We found that lattice constant a of the Si1−xGex alloys increased linearly with the composition parameter x. Average diameters of the single-phase nanoparticles were estimated to be between 3-10 nm. Further evidence of FCC single-phase nanoparticles has been obtained by high resolution transmission electron microscopy. From absorption spectra, the gradual shift of the direct phononless transition identified for the E1 point in the Brillouin zone of bulk Ge is observed in single-phase Si1−xGex nanoparticles as a function of the composition parameter x.