Characterization of strain relaxation in low-defect-density thin single and step-graded germanium buffer layers by high-resolution two-dimensional x-ray diffraction mapping

Double-crystal x-ray diffraction rocking curves and two-dimensional recipro cal space mapping (2D-RSM) are utilized to characterize the degree of strai n relaxation, lattice parameters and assessment of defect propagation in tw o growth approaches to yield relaxed germanium buffer layers on silicon sub strates. Two schemes are investigated: direct epitaxy of a single relaxed b uffer layer (SE-RBL) and step-graded multiple relaxed buffer layers (GM-RBL s). The characteristics of these two growth schemes offer prospects of a mu ch thinner grown layer compared with previously reported approaches. Two-di mensional reciprocal space mapping shows that an SE-RBL with a thickness of less than 0.35 mu m has a superior quality over the GM-RBLs. A high relaxa tion 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 width a t half maximum of the layer to substrate FWHM (L/S) of nearly unity for bot h omega and omega/2 theta scan directions imply a very high-quality crystal line relaxed buffer layer is realized. The 2D-RSM of the material deposited using the GM-RBL scheme, the first of its kind regarding the total grown t hickness (approximately 6 mu m), also show a mosaic final Ge buffer layer w ith an indication of reduction of dislocation density.