Characterization of strain relaxation in low-defect-density thin singleand step-graded germanium buffer layers by high-resolution two-dimensionalx-ray diffraction mapping

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Double-crystal x-ray diffraction rocking curves and two-dimensionalreciprocal space mapping (2D-RSM) are utilized to characterize the degree ofstrain relaxation, lattice parameters and assessment of defect propagation intwo growth approaches to yield relaxed germanium buffer layers on siliconsubstrates. Two schemes are investigated: direct epitaxy of a single relaxedbuffer layer (SE-RBL) and step-graded multiple relaxed buffer layers(GM-RBLs). The characteristics of these two growth schemes offer prospects ofa much thinner grown layer compared with previously reported approaches.Two-dimensional reciprocal space mapping shows that an SE-RBL with a thicknessof less than 0.35 µm has a superior quality over the GM-RBLs. A highrelaxation factor (R = 0.986±0.002) is obtained from the asymmetric (113)2D-RSM of the SE-RBL with 100% Ge content. Further, the ratios of full widthat half maximum of the layer to substrate FWHM (L/S) of nearly unity forboth ω and ω/2θ scan directions imply a very high-qualitycrystalline relaxed buffer layer is realized. The 2D-RSM of the materialdeposited using the GM-RBL scheme, the first of its kind regarding the totalgrown thickness (approximately 6 µm), also show a mosaic final Gebuffer layer with an indication of reduction of dislocation density.