The onset of misfit dislocation formation, i.e., the critical thickness for heteroepitaxy, is studied for selective epitaxial growth of high Ge-content, strained SiGe on oxide-patterned Si wafers. Misfit dislocation spacing was analyzed as a function of film thickness using plan-view transmission-electron microscopy. For selective epitaxial growth at 450 °C, the critical thickness for Si0.33Ge0.67 is found to be 8.5 nm. This is a twofold increase compared to the 4.0 nm theoretical equilibrium critical thickness and the 4.5 nm critical thickness measured for growth on bare Si wafers. The misfit dislocation density for selective epitaxial growth is strongly influenced by the shape and orientation of the growth area.

Si-core/Ge-shell nanowire p-channel metal-oxide-semiconductor-field-effect-transistors with high-permittivity-dielectric/metal-gate have been demonstrated by selective epitaxial growth of Ge thin-films on the Si-nanowires fabricated by a top-down scheme. Cross-sectional transmission-electron-microscopy reveals that the epitaxial Ge shell exhibits hexagonal {111} facets, and that the Ge is defected, particularly near the Si corners. The hole mobility increases by 40% as the Si-core size is decreased from 70 to 20 nm. Finite-element simulations of the stress profile induced in the Ge channel by the gate stack suggest that a transformation in the transverse stress component from compression to tension plays a role in the mobility enhancement.

Ultrathin strained-Si/strained-Ge heterostructures on insulator have been fabricated using a bond and etch-back technique. The substrate consists of a trilayer of 9 nm strained-Si/4 nm strained-Ge/3 nm strained-Si on a 400-nmthick buried oxide. The epitaxial trilayer structure was originally grown pseudomorphic to a relaxed Si 0.5 Ge 0.5 layer on a donor substrate. Raman analysis of the as-grown and final transferred layer structures indicates that there is little change in the strain in the Si and Ge layers after layer transfer. These ultrathin Si and Ge films have very high levels of strain ($1.8% biaxial tension and 1.4% compression, respectively), and are suitable for enhancedmobility field-effect transistor applications.

The goal of this work is to study and optimize the growth parameters for Ge-on-Si for photodiodes operating at 1.55 um. Approximately 1 um-thick, relaxed Ge is grown in exposed Si regions on oxide-patterned Si wafers. Germanium selectivity, faceting, morphology, and threading dislocation density are investigated as a function of growth and processing conditions. Ge faceting was reduced by increasing the growth temperature and germane partial pressure, and at the optimized growth condition of 750{degree sign}C and 10T, an RMS surface roughness of 1.3 nm was obtained for 10 x 10 um AFM scans. Threading dislocation density was reduced for structures smaller than 5 um, but the dislocation density depends on post-growth annealing conditions and Ge film thickness.