Growth of Tetragonal Si via Plasma-Enhanced Epitaxy

We have been able to synthesize directly the tetragonal Si by low temperature plasma-enhanced chemical vapor deposition using hydrogen and silane as the precursor and carrier gas, respectively. With the optimization of growth conditions, a stable tetragonal epitaxial Si can be grown on a crystalline Si substrate at large scale. By combining X-ray diffraction and high resolution transmission electron microscopy measurements, we found that the epitaxial layer has smaller in-plane but larger out-of-plane lattice parameters as compared to the crystalline substrate. The existence of hydrogen platelets in epitaxy is also observed, which affects the diffraction patterns along that direction. We attribute the formation of tetragonal Si to the hydrogenated-cluster-assisted epitaxy. Other possible reasons including host sites of hydrogen atoms and thermal expansion coefficients are also discussed.