Characterization of highly boron-doped Si, Si1-xGex and Ge layers by high-resolution transmission electron microscopy

Cross-sectional transmission electron microscopy (XTEM) has been used to characterize the defect structure of as-grown and annealed highly boron-doped Si, Si1-xGex (x less than or equal to 0.18) and Ge layers grown by molecular beam epitaxy. The structures have also been analyzed with two-dimensional (2D) reciprocal space mapping using high-resolution X-ray diffraction (HRXRD). The boron concentration (C-B) was in the range from 3 X 10(19) to 8 X 10(20) cm(-3). Si and Si1-xGex layers were grown at 400 degrees C and Ge layers at 325 degrees C. XTEM micrographs show no crystalline defects in Si and Si1-xGex samples for C-B less than or equal to 3 X 10(20) cm(-3). However, for C-B = 8 X 10(20) cm(-3), B precipitation in the form of epitaxial layer (2D) precipitates on (001) planes in Si and Si1-xGex and both (001) and (113) planes in Ge was observed. After annealing the B-doped Si and SiGe samples with C-B = 8 X 10(20) cm(-3) at 1000 degrees C for 15 min, a large number of discrete, 3D, B-related precipitates were observed. For B-doped Ge samples, the thermal stability was poor and B precipitation and severe roughening were observed after annealing at 650 degrees C for 15 min.