CHARACTERIZATION OF MISMATCHED SIGE GROWN ON LOW-TEMPERATURE SI BUFFER LAYERS BY MOLECULAR-BEAM EPITAXY

Several types of buffer layer structures, including superlattice and s tep-graded layers, have been employed to reduce the threading dislocat ion in SiGe epitaxial layers. A new technique, using a 0.1 mu m thick Si buffer grown at 450 degrees C by molecular beam epitaxy, provides t he best results. For a 0.5 mu m thick Si0.85Ge0.15 layer, the dislocat ion density is less than or equal to 10(5) cm(-2). Hall measurements i ndicate an improvement in the hole mobility of a 1 mu m thick Boron do ped Si0.7Ge0.3 layer. A SiGe/Si heterojunction bipolar transistor has been fabricated exploiting the low temperature Si buffer. Transmission electron microscopy of the structure does not indicate any evidence o f threading dislocations.