X-RAY-DIFFRACTION INVESTIGATION OF SINGLE STEP AND STEP-GRADED SIGE ALLOY BUFFERS FOR THE GROWTH OF SHORT-PERIOD SI(M)GE(N) SUPERLATTICES USING RECIPROCAL SPACE MAPPING

Double crystal and triple axis x-ray diffractometry was used to characterize the structural properties of short period Si6Ge4 superlattices grown by molecular beam epitaxy on either a thin (20 nm) single step Si0.6Ge0.4 alloy buffer or on a thick step-graded Si1-xGex(0 < x < 0.4, 700 nm thick) buffer followed by a 550 nm Si0.6Ge0.4 layer. Reciprocal space maps around the (004) and (224) reciprocal lattice points yield direct information on the strain status of the buffer and superlattice layers. For the thick step-graded buffer indeed all layers with different Ge content are fully relaxed and thus the growth of an almost freestanding superlattice is possible.