Characterization of highly boron-doped Si, Si 1 − xGe x and Ge layers by high-resolution transmission electron microscopy

Abstract

Cross-sectional transmission electron microscopy (XTEM) has been used to characterize the defect structure of as-grown and annealed highly boron-doped Si, Si 1 − x Ge x ( x ≤ 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 × 10 19 to 8 × 10 20 cm −3. Si and Si 1 − x Ge x layers were grown at 400°C and Ge layers at 325°C. XTEM micrographs show no crystalline defects in Si and Si 1 − x Ge x samples for C B ≤ 3 × 10 20 cm −3. However, for C B = 8 × 10 20 cm −3, B precipitation in the form of epitaxial layer (2D) precipitates on (001) planes in Si and Si 1 − x Ge x and both (001) and (113) planes in Ge was observed. After annealing the B-doped Si and SiGe samples with C B = 8 × 10 20 cm −3 at 1000°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°C for 15 min.