Increasing the critical thickness of SiGe layers on Si substrates using sputter epitaxy method

Abstract

SiGe layers were formed on Si substrates by using the sputter epitaxy method. The growth temperatures were 400 and 560 °C, and the growth rates of the SiGe layers were about 2.7–5.4 nm/min, depending on the Ge composition ratio. The samples formed by gas-source molecular beam epitaxy (GSMBE) were also fabricated for comparison. The lattice-mismatch ratio was investigated using X-ray diffraction, the surface roughness was observed by an atomic force microscope, and the crystallinity of the SiGe layers was observed by a transmission electron microscope. The critical thickness of the SiGe layers was estimated from the lattice-mismatch ratio, and the critical thickness at a growth temperature of 400 °C was higher than that in the GSMBE and previous reports. The surface roughness of the Si1-xGex layers (x = 0.24–0.51) with no strain relaxation was flat and below 1 nm. Without any buffer techniques, high Ge content SiGe layers with no strain relaxation were directly formed on Si substrates using the sputter epitaxy method. It is considered that the sputter epitaxy method can grow SiGe layers at relatively low temperatures and can increase the critical thickness.