Reduction of dislocation density of MBE-grown Si 1− xGe x layers on (100) Si by rapid thermal annealing

Abstract

Si 1− x Ge x layers with overcritical thicknesses grown on (100 Si by molecular beam epitaxy (MBE) were characterized by Rutherford backscattering/channeling (RBS), transmission electron microscopu (TEM) and Nomarski differential interference contrast (NDIC) microscopy. The influence of growth temperature and subsequent furnace annealing or rapid thermal annealing (RTA) on crystal quality and surface morphology was investigated. Microstructural investigations by TEM of plane-view and cross-section specimens show an array of misfit dislocations at the interface with the substrate as well as threading dislocations which extend from the interface to the surface. RTA up to 1150°C led to a significant reduction of the threading dislocation density. The minimum yield ξ min of a sample grown at 450°C decreased from 6.7 to 3.9% after RTA at 1100°C for 30s. NDIC microscopy shows that the surface remains smooth after RTA in contrast to in-situ thermal annealing and ex situ furnace annealing. Similar experiments were carried out with pure germanium layers on (100) Si. RTA up to 600°C leads to an improvement of crystal quality. Higher temperatures result in the formation of square-shaped holes.