SIGE EPITAXY WITH GRADED BUFFER BY ULTRAHIGH-VACUUM CHEMICAL-VAPOR-DEPOSITION

A SiGe/Si epilayer with a linear-step-graded buffer was grown by ultra high vacuum chemical vapor deposition technique at a relatively high g rowth temperature (780 degrees C) and a relatively high growth rate. A lmost linear Ge content variation was realized in the buffer layer due to the Ge segregation to the growing surface during epitaxial growth. Double crystal x-ray diffraction and Raman spectroscopy show that the upper layer is fully relaxed. However, the measured results show that the density of dislocation in the composition graded structure is muc h lower than that in single-step epilayer structures.