Relaxed Si_1-xGe_x/Si_1-x-yGe_xC_y buffer structures with low threading dislocation density

We demonstrate the growth of a relaxed, only 1 μm thick, stepwise graded buffer based on a combination of Si_1-xGe_x and Si_1-x-yGe_xC_y. This buffer concept relies on the retardation of dislocation glide in Si_1-x-yGe_xC_y relative to strain equivalent Si_1-x-yGe_x. on silicon. The homogeneous Si_1-x-yGe_x layer with x = 30% on top of the buffer structure is (73±5)% relaxed. For the nonoptimized buffer growth, we already find a threading dislocation density below 10⁵ cm^-2. A stepped Si_1-xGe_x buffer with the identical thickness and strain profile grown with the same temperature ramp yields a threading dislocation density above 10⁷ cm^-2. This indicates that the addition of carbon is a promising way for new relaxed buffer concepts with low threading dislocation densities.