Non-selective thin SiGe strain-relaxed buffer layers: Growth and carbon-induced relaxation

As an economically more attractive alternative to the classical thick graded strain-relaxed SiGe Buffer layers (SRB), we have developed a thin SRB based on a 200-nm-thick homogeneous Si0.8Ge0.2 layer with a C-doping spike inserted in about the middle of the layer. This C-doping layer enhances strongly the relaxation of the layer to ∼ 80%, when compared to samples without C layer. The thin SRB shows threading defect densities ≤ 107/cm2 and a very smooth surface (RMS < 1 nm). The relaxation mechanism appears to be very similar to the “Modified Frank Read” (MFR) mechanism as developed by Legoues et al. [F. Legoues, B. Meyerson, J. Morar and P. Kirchner; J. Appl. Phys. 71 (1992) 4230.]. In our case, the MFR source for dislocation nucleation may consist of tiny SiC precipitates.