A surfactant-mediated relaxed Si0.5Ge0.5 graded layer with a very low threading dislocation density and smooth surface

A method to grow a relaxed Si0.5Ge0.5 graded layer with a very smooth surface and a very low threading dislocation density using solid-source molecular-beam epitaxy is reported. This method included the use of Sb as a surfactant for the growth of a 2 mu m compositionally graded SiGe buffer with the Ge concentration linearly graded from 0% to 50% followed by a 0.3 mu m constant Si0.5Ge0.5 layer. The substrate temperature was kept at 510 degrees C during the growth. Both 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 show a surface root mean square roughness of only 20 Angstrom. The threading dislocation density was determined to be as low as 1.5x10(4) cm(-2) as obtained by the Schimmel etch method. This study shows that the use of a Sb surfactant and low temperature growth is an effective method to fabricate high-quality graded buffer layers. (C) 1999 American Institute of Physics. [S0003-6951(99)03837-1].