Investigation of the temperature stability of germanium-rich SiGe layers on Si(111) substrates

Abstract

In this work, we investigated fully relaxed SiGe and pure Ge layers on Si(111) substrates, regarding their temperature stability. The layers were annealed at various temperatures up to 650 °C directly after growth. The Ge content of the Si1−xGex layers was varied between 0.6 and 1. We investigated effects due to surface segregation of Ge in the SiGe layers. During heat treatment, different surface reconstructions were observed. The SiGe layers remained smooth with a root-mean square surface roughness below 0.5 nm up to temperatures of 500 °C and a 7 × 7 surface reconstruction was seen. Annealing at higher temperatures corresponding to a 7 × 7–“1 × 1” phase transition, the surface roughness increased to more than 2 nm and island formation was observed. We measured the in-plane lattice constant of the surface as a function of temperature and confirmed a strong effect of Ge segregation on the surface strain. The Ge accumulation at the surface was confirmed by angle-resolved X-ray photoelectron spectroscopy. The high adatom density of the “1 × 1” reconstruction in combination with compressive strain led to island nucleation when cooling down. Pure Ge layers remained smooth even after annealing up to 650 °C.