Lattice parameters and local atomic structure of silicon-rich Si-Ge/Si (100) films

The lattice parameters and Ge-to-Si nearest-neighbor and next-nearest-neighbor distances were measured using x-ray rocking curves and extended x-ray-absorption fine-structure spectroscopy for four different Si-rich Si1-xGex/Si(100) epitaxial films. The Si-Ge films, two prepared by molecular-beam epitaxy and two by chemical-vapor deposition, had thicknesses of 500-900 and Ge concentrations of xGe=0.060.18. Lattice parameters of the films, corrected for coherency strain, agreed with values reported for bulk Si-Ge alloys. Ge-to-Si distances were 2.375±0.02 and 3.85±0.06 for nearest and next-nearest neighbors, respectively, and were independent of Ge concentration within these experimental uncertainties. A simple, random-solid-solution model using composition-independent values for nearest-neighbor distances rSi-Si, rGe-Ge, and rGe-Si reproduced the average nearest-neighbor distance r(xGe) deduced from observed lattice parameters a(xGe) for our range of Ge concentrations. Composition variations of interatomic distances expected from various theoretical models [Martins and Zunger, Phys. Rev. B 30, 6217 (1984); Shih et al., B 31, 1139 (1985); Thorpe and Garboczi, Bull. Am. Phys. Soc. 35, 781 (1990)] all fell within our experimental uncertainty of ±0.02. © 1991 The American Physical Society.