Electron microscopy study of surfactant-mediated solid phase epitaxy of Ge on Si(111)

The effect of As surfactant on solid phase epitaxy (SPE) of Ge on Si(lll) has been investigated using in situ scanning electron microscopy and ex situ transmission electron microscopy. As surfactant is supplied to an amorphous Ge film in four different ways: co-deposition with the Ge film, deposition on the Si substrate, deposition on each interface of 3-nm-thick Ge films in a multilayered structure, and deposition on the surface of a Ge film. As at the Ge/Si interface has a limited effect in suppressing island growth with a critical thickness of about 20 monolayers (ML). Thicker film growth is achieved by the other three SPE methods. Although the surface morphology slightly differs, the crystalline quality is almost the same for all cases. An As surfactant on the surface of amorphous Ge increases the crystallization temperature by 100 degrees C compared to the Ge islands;temperature without As. This indicates that an As overlayer inhibits structural relaxation on amorphous film by suppressing surface diffusion of Ge atoms, thus changing the growth mode. In other SPE methods, surface passivation with As due to segregation during deposition may also be responsible for the suppression of islands.