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The incorporation behavior of Er into Si and Si 0.88 Ge 0.12 using ErF 3 and Er 2 O 3 as dopant sources during molecular beam epitaxy has been studied. The Er-compounds were thermally evaporated from a high-temperature source. Dissociation of Er 2 O 3 took place and reaction with graphite parts in the high temperature source gave an increased CO background pressure and evaporation of metallic Er. Surface segregation of Er may be strong, but with a high CO or F background pressure, the surface segregation could be reduced and sharp Er concentration profiles were obtained. Transmission electron microscopy analysis shows that it is possible to prepare high crystalline quality structures with Er concentrations up to 4×10 19 cm −3 using Er 2 O 3 and a high F background pressure. Using ErF 3 compound as source material a F/Er incorporation ratio of approximately three has been measured by secondary ion mass spectrometry. Fluorine incorporation can occur not only from evaporated units of ErF 3 molecules, but also from CF x ( x =1–4) and F background species, which are present due to a reaction between the ErF 3 source material and the graphite crucible in the source. After careful degassing of the source, the partial pressures of these species can be significantly reduced. By producing an Er-doped multilayer structure consisting of alternating doped layers grown at low temperature (350°C) and undoped layers grown at a higher temperature (630°C), a flat surface could be maintained during the growth sequence. In this way it was possible to prepare Er-doped structures with an average Er concentration of 1×10 19 cm −3 and without observable defects using ErF 3 as source material. For the case of Er-doping of Si 0.88 Ge 0.12 using ErF 3 , we observed contrast along lines in the growth direction at an Er concentration of 1×10 19 cm −3 , which was attributed to Si concentration variations. Intense emission related to Er has been observed by electro- and photoluminescence.

Two-dimensional (2D) reciprocal space mapping of high-resolution X-ray diffraction has been used to characterize the strain in structures with Ge1−xSix and heavily B-doped Ge layers grown by molecular beam epitaxy on Ge (001). Tetragonal lattice distortion yielding strain along and perpendicular to the surface has been determined for Si fractions from 10 to 40% and B concentrations in the range from 6 × 1019 to 8 × 1020cm−3. A sensitive estimate of the critical thickness for Ge1−xSix layers grown on Ge has been obtained by analyzing 2D-reciprocal space maps around the (113) reflection. The lattice contraction coefficient due to B doping in Ge was β = 4.3 × 10−24cm3 per B atom. For CB ≥ 2.2 × 1020cm−3, B precipitation in the form of epitaxial interfacial layers on (001) and (113) planes in the Ge was observed by cross-sectional transmission electron microscopy. Electrical characterization of the samples showed that doping concentrations ≤ 2 × 1020cm−3 could be fully activated.

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.

Design, performance test, doping capability and grown material quality of a Balzers UMS 630 Si MBE system are reported, particularly concerning measures to obtain good quality of grown films. Good stability, reproducibility and uniformity of deposition rates (Si and Ge) and doping concentrations (Sb and B) have been obtained for growth on a 4 inch Si wafer with sample rotation using a mass-spectrometry controlled e-beam evaporation system, and home-made doping sources, respectively. The quality of grown undoped and modulation doped Si and SiGe layered structures were evaluated using high-resolution XRD, XTEM, SIMS, Hall, and PL measurements. Intense and sharp excitonic PL transitions and high carrier mobility obtained from the grown Si SiGe heterostructures and quantum wells grown at a wide substrate temperature range (320–650°C) indicate high crystalline quality of grown films. Finally, test HBT structures with a thin SiGe base have been made. Good dc characteristics and frequency performance were obtained.