Surfactant-mediated growth of germanium on Si(100) by MBE and SPE

Abstract

Germanium layers of 10 and 30 nm thickness have been grown on Si(100) with and without antimony as a surfactant by molecular beam epitaxy (MBE) and solid phase epitaxy (SPE) and investigated in situ by RHEED and XPS and ex situ by TEM and XRD. Without a surfactant germanium growth proceed in a typical Stranski-Krastanov mode. The system is minimizing its built-in strain energy by undergoing strain relaxation through a clustering mechanism (islanding). In all surfactant-mediated growth processes it was possible to obtain smooth layers without island formation. The influence of different ways for introducing the surfactant layer (at the interface between substrate and growing film, in the growing film below or above the critical Stranski-Krastanov thickness, or on top of the grown Ge film) will be presented. Especially in surfactant-controlled SPE, the smooth epitaxial germanium layer was obtained by passing through an island formation stage. These islands formed below 400°C are of different structure than the ones formed without a surfactant. Possible mechanism for the “smoothing out” of islands developed in the beginning stage of surfactant-controlled SPE will be discussed. The island formation stage can be completely suppressed by depositing the surfactant on top of the amorphous Ge layer before increasing the temperature.