Combined high resolution X-ray diffraction and EXAFS studies of Si (1− x) Ge x heterostructures

Abstract

In this paper, we compare the structural information obtained by measuring X-ray diffraction reciprocal space maps and by EXAFS analysis on two Si (1− x) Ge x alloys with low (LC) and high (HC) Ge concentration. From the analysis of the X-ray diffraction maps we determined the alloy lattice parameters for the cubic cell ( a=5.58 Å) of the fully relaxed HC sample and for the tetragonal cell ( a=5.43 Å, c=5.46 Å) of the fully strained LC sample and from these values the Ge alloy content (HC: x=0.66±0.04, LC: x=0.048±0.003). The EXAFS data were taken at the Ge k-edge for incident wave polarization directions either parallel or perpendicular to the surface plane. The satisfactory correlation found between the Ge coordination ratio and the Ge–Si and Ge–Ge distances, derived by best-fitting the EXAFS curves, and the X-ray diffraction structural parameters indicates that the combination of the two techniques is a unique approach to achieve a thorough characterization of the structural and chemical properties of lattice mismatched heterostructures.