Annealing experiments on supercritical Si_1-x Ge_x layers grown by RPCVD

This paper presents a study of the relaxation mechanisms for SiGe epitaxy performed by reduced pressure chemical vapor deposition (RPCVD) in a commercially available single wafer epitaxial reactor. The samples were grown at 500°C and an overall pressure of 40 Torr, with SiH₂Cl₂ and GeH4 as precursor gasses. In contrast to the situation for molecular beam epitaxy (MBE), we found that under RPCVD conditions the relaxation by 3D-growth was strongly suppressed. Relaxation then occurred by the development of misfit dislocations even in the case of high Ge-concentrations (>40%). This behavior is attributed to the high hydrogen coverage of the substrate surface during the RPCVD, which reduces the surface migration of the adsorbed species. Furthermore, the relaxation mechanism has been studied in annealing experiments where wave and island formation was observed. The annealing experiments clearly confirm that surface migration plays a significant role for 3D-growth. Using the annealing procedure layers of high island density and strong photoluminescence have been produced.