MEASUREMENTS OF ALLOY COMPOSITION AND STRAIN IN SI1-XGEX LAYERS BY USING DOUBLE-CRYSTAL X-RAY-DIFFRACTION

Si1-xGex epilayers with varying Ge compositions and thicknesses have b een grown on Si by molecular beam epitaxy. The Ge content and the degr ee of relaxation of the epilayers were measured by double-crystal x-ra y diffractometry (DCXD). The Ge compositions obtained by DCXD were in good agreement with those obtained from Rutherford backscattering meas urements, having an accuracy of about +/-10% of the estimated Ge conte nt in the range 0 < x < 0.4. The residual strain was roughly proportio nal to the inverse of the thickness, in agreement with the mechanical equilibrium theory of Matthews and Blakeslee, while the critical thick nesses were significantly larger than those predicted by the equilibri um model. Furthermore, the residual strain depended upon the Ge compos ition as well as the thickness. These results can be explained by inco rporating composition-dependent frictional forces in the equilibrium m odel.