Epitaxial Ge_xSi_1-x/Si (100) structures produced by pulsed laser mixing of evaporated Ge on Si (100) substrates

Heteroepitaxial Ge_xSi_1-x alloy layers have been formed by pulsed laser induced mixing of pure germanium films and Si (100) substrates. Ge films 50-200 Å thick are electron beam evaporated onto Si (100) under ≤1×10^-7 Torr vacuum. The near surface of the sample then undergoes a rapid melt and regrowth process using 2-10 pulses from a XeCl excimer laser. The laser has a 37-ns pulse width at 308 nm and its energy density of 0.5-1.5 J/cm² is precisely homogenized into a 4×4 mm square area. The alloy layers are 250-1600 Å thick, have a Ge fraction x=2.5-19%, and exhibit excellent crystallinity as evaluated by MeV ion channeling and lattice resolution cross-sectional transmission electron microscopy. Unlike layer growth by molecular beam epitaxy, this approach is insensitive to minor levels of contamination because the original Ge/Si interface is melted through during the laser processing.