Control of surface flatness of Ge layers directly grown on Si (001) substrates by DC sputter epitaxy method

The formation of Ge layers on Si (001) substrates with 3.5 Ω cm resistivity by the sputter epitaxy method with DC magnetron sputtering has been investigated. The surface morphology of Ge layers grown on Si substrates depends on the sputtering power and the deposited film thickness of Ge. At the initial stage of film deposition, the higher sputtering power yields smaller and more closely packed Ge islands due probably to an increase in the collision rate of the Ge atoms migrating on the Si substrate, which preserves more compressive strains in the films. With the preserved strains, the surface roughening derived from the strain relaxation is reduced. Furthermore, the surface flatness can be improved with the initially smaller islands and additional deposition; this is probably due to the effect of Ge adatom anchoring at concave areas where many bonding sites are available for stable Ge residence. The root-mean-square surface roughness of a 200-nm-thick Ge layer formed at a sputtering power of 100 W is about 0.23 nm.