Pulsed laser assisted epitaxy of Ge_xSi_1-x alloys on Si 〈100〉

The epitaxial quality of Ge_xSi_1-x films grown on Si〈100〉 by a novel laser-assisted technique has been investigated for compositions in the range x≤0.37 and thicknesses between 50 and 500 nm. Epitaxy is induced during electron beam deposition of Ge_xSi _1-x films on Si substrates by pulses of an excimer laser operating at 308 nm with 30 ns pulse duration. Good epitaxial growth is obtained for 50 nm films for x≤0.04 on chemically cleaned Si(100) surfaces even in the presence of substantial fluorine coverage. Using a predeposition/crystallization of a 50 nm pure-Si buffer layer, good epitaxy is then obtained in 50 nm films for x=0.05-0.13. At x=0.07, defect-free alloys have been grown up to thicknesses of 0.5 μm. However, for films with compositions above 19 at.% Ge, dislocations at a nearly constant density of ≊10 μm/μm² are observed. This uniform density suggests a breakdown mechanism other than simple strain relaxation.