Reverse graded relaxed buffers for high Ge content SiGe virtual substrates

An innovative approach is proposed for epitaxial growth of high Ge content, relaxed Si(1-x)Ge(x) buffer layers on a Si(001) substrate. The advantages of the technique are demonstrated by growing such structures via chemical vapor deposition and their characterization. Relaxed Ge is first grown on the substrate followed by the reverse grading approach to reach a final buffer composition of 0.78. The optimized buffer structure is only 2.8 mu m thick and demonstrates a low surface threading dislocation density of 4x10(6) cm(-2), with a surface roughness of 2.6 nm. The buffers demonstrate a relaxation of up to 107%.