Step-wise equilibrated graded Si1-xGex buffer layers, where x was less than 0.2, were prepared. The threading dislocation densities were as low as 102/cm2. The samples were characterized by means of photoluminescence spectroscopy and transmission electron microscopy. It was found that there was a dependence of the defect-related photoluminescence spectra upon the concentration and morphology of the various types of defect which existed in the buffers. In particular, there was a correlation between the D3 line intensity and the threading dislocation density in the cap layer on SiGe buffers with various degrees of relaxation. It was noted that there was an increase in the signal intensity of the D1/D2 lines upon removing the cap layer and the upper part of the buffer. This suggested that the misfit dislocation networks in the remaining part of the buffer were directly related to the D1 and D2 peaks.

H.B.Erzgräber, G.Kissinger, G.Morgenstern, T.Morgenstern: Solid State Phenomena, 1996, 47-48, 529-34