Control of Sn Precipitation and Strain Relaxation in Compositionally Step-Graded Ge1-xSnx Buffer Layers for Tensile-Strained Ge Layers

We investigated the relationship between Sri precipitation and strain relaxation in Ge1-xSnx buffer layers grown by the compositionally step-graded (CSG) method on a virtual Ge substrate. We found that the strain in the upper Ge1-xSnx layers is reduced by Sri precipitation rather than the lateral propagation of misfit dislocations at the interfaces of upper Ge1-xSnx layers in the CSG method. The critical misfit strain was increased to 5.8 x 10(-3) compared with that in our previous work by lowering the temperature of the postdeposition annealing, and a Sri content of 6.3% in the Ge1-xSnx buffer layer was achieved with a large degree of strain relaxation using only two stacked layers of the CSG structure. An in-plane tensile strain of 0.62% in a 30-nm-thick Ge layer fabricated on these Ge1-xSnx buffer layers was achieved. (C) 2009 The Japan Society of Applied Physics