Direct assessment of relaxation and defect propagation in different as-grown and in situ post-growth annealed thin Ge/Si and step-graded Si1-xGex/Si buffer layers

The strain-sensitive X-ray two-dimensional reciprocal space mapping diffrac trometry(2D-RSM) is employed to investigate the relaxation parameters and d efect propagation in various thin relaxed buffer layers (RBLs) having a pur e Ge top. In addition, we also studied the effect of in situ post-growth th ermal treatments at an early growth stage of RBLs with low and intermediate Ge fraction. Both direct Ge epitaxy and multi-layer step-graded epitaxy ha ve been adopted to grow these RBLs using chemical vapor deposition (CVD) at elevated partial pressure (around 10 Torr), which implies a much higher gr owth rate than RBLs grown using ultra-high vacuum CVD technique. Fully rela xed Ge top layers were obtained for both the direct Ge epitaxy, as well as for the step-graded technique. The results, when comparing these two techni ques, favor the direct Ge epitaxy. However, the results of in situ post-gro wth annealing of the step-graded RBLs indicate a large reduction in the thr eading dislocations present in the grading regions without a change of rela xation degree or Ge% incorporation in that region. (C) 2001 Elsevier Scienc e Ltd. All rights reserved.