A solid-source molecular beam epitaxy method was described for growing relaxed Si0.5Ge0.5 graded layers having a very smooth surface and a very low threading dislocation density. The method included the use of Sb as a surfactant for the growth of a 2μm SiGe buffer layer in which the Ge concentration was linearly graded from 0 to 50%, followed by an 0.3μm-thick uniformly Si0.5Ge0.5 layer. The substrate temperature was kept at 510C during growth. Raman scattering and X-ray diffraction were used to determine the Ge mole fraction, and the degree of strain relaxation. Both X-ray reflectivity and atomic force microscopy measurements revealed a surface root-mean square roughness of 2nm. The threading dislocation density was as low as 1.5 x 104/cm2; according to Schimmel etching results.

A Surfactant-Mediated Relaxed SiGe Graded Layer with a Very Low Threading Dislocation Density and Smooth Surface J.L.Liu, C.D.Moore, G.D.U'Ren, Y.H.Luo, Y.Lu, G.Jin, S.G.Thomas, M.S.Goorsky, K.L.Wang: Applied Physics Letters, 1999, 75[11], 1586-8