Dislocation-related photoluminescence in Si 1−xGe x/Si(100) grown by molecular beam epitaxy

Abstract

Photoluminescence (PL) in Si 1−xGe x alloys grown on Si(100) by molecular beam epitaxy (MBE) has been studied over the composition range 0≦χ≦0.5. For x≧0.15, strong deep-level luminescence has been observed. Sharp lines which are similar to the dislocation-related D-lines in Si appear in the spectra for x=0.15 and 0.26. Transmission electron microscopy (TEM) for these samples reveals that there are a lot of dislocations at the Si 1−xGe x/Si interface and in the Si substrate. The dislocations in the Si substrate are considered to be the origin of the sharp luminescence lines. These PL lines for x=0.15 cannot be observed in the case of thin layers. In that case, the density of the dislocations near the interface is much lower. For x=0.38 and 0.50, broad bands appear in the spectra. The TEM observations in these cases reveal that there are many dislocations in the Si 1−xGe x layers and that the dislocation density in the Si substrate is very low. The broad bands are considered to originate from the dislocations in the Si 1−xGe x layer.