An investigation was made of the surface roughness and dislocation distribution of compositionally graded relaxed SiGe buffer layers by inserting two tensile-strained Si layers. The 20nm thick strained Si layers, less than the critical thickness for dislocation formation, were inserted at 10 and 20%Ge content regions of the 1µm thick graded SiGe layer with a final Ge content of 30%. The surface immediately after growing the second strained Si layer on SiGe with 20%Ge content was found to be flat with about 1.1nm root-mean-square roughness. However, the cross-hatched surface with the 7.8nm roughness develops during subsequent SiGe growths, which was slightly less than the 10.3nm value for SiGe without inserted Si layers. Another important issue of consideration was that inserting the strained Si layers leads to increased interaction among dislocations as shown by cross-sectional transmission electron microscopy. This study explores the possibility of using strained layers for achieving flat surfaces and illustrates the need for optimization when using this approach.

Surface Roughness and Dislocation Distribution in Compositionally Graded Relaxed SiGe Buffer Layer with Inserted-Strained Si Layers. T.S.Yoon, J.Liu, A.M.Noori, M.S.Goorsky, Y.H.Xie: Applied Physics Letters, 2005, 87[1], 012104 (3pp)