The real-time stress evolution was investigated during the molecular-beam epitaxial growth of GaAs1–xSbx/GaAs metamorphic buffer. These real-time data were obtained using an in situ multi-beam optical sensor measurement and was combined with detailed analysis of data obtained from X-ray diffraction, transmission electron microscopy, and atomic force microscopy. The strain relaxation of two different compositions of GaAs1–xSbx was compared, and correlated with the development of dislocation structure and morphology. Several distinct stages of the strain relaxation were observed during growth, which could be separated in three main regimes: pseudomorphic growth, fast strain relaxation, and saturation. Transmission electron microscopy data showed that GaAs0.5Sb0.5 buffer layers had a larger fraction of pure-edge dislocations that arise during the early stages of growth. This could had a significant influence in the fabrication of buffer layers, since pure edges were favoured over the threading dislocations. The strain relaxation profile for each film was modelled by using a modified Dodson-Tsao model that took account of the elastic interactions of misfit dislocations. The model results agreed with experimental data and showed that the interaction of misfit dislocations was responsible for the large residual stress. In addition, following the Dodson-Tsao description developed for the rate of dislocation multiplication, it was possible to determine the line density of threading dislocations from the experimental data. This had potential application in the design of metamorphic buffer layers, because the observations were made in real time on individual growths, without the need of external characterization to measure the dislocation density.

Dislocation Dynamics in Strain Relaxation in GaAsSb/GaAs Heteroepitaxy. B.P.Rodríguez, J.M.Millunchick: Journal of Applied Physics, 2006, 100[4], 044503 (7pp)