The growth of a relaxed 1μ-thick step-wise graded buffer, based upon a combination of SiGe and SiGeC, was studied. The buffer method depended upon the retardation of dislocation glide in the SiGeC, relative to that in SiGe, under equivalent strains on Si. An homogeneous Si1-xGex layer, with x = 0.30, on top of the buffer structure was 73% relaxed. In the case of non-optimized buffer growth, the threading dislocation density was already below 105/cm2. A stepped SiGe buffer with an identical thickness and strain profile, grown using the same temperature ramp, yielded a threading dislocation density of more than 107/cm2. This suggested that the addition of C was a promising means of producing relaxed buffers with low threading dislocation densities.

H.J.Osten, E.Bugiel: Applied Physics Letters, 1997, 70[21], 2813-5