An annealing study of strain relaxation and dislocation generation in Si1−xGex/Si heteroepitaxy

Abstract

The generation of interface misfit dislocations, and the accompanying strain relaxation, in a molecular-beam epitaxy grown 0.17 μm thick metastable Si0.82Ge0.18/Si(100) strained epilayer have been studied in detail as a function of rapid thermal annealing treatments over the 500–850 °C temperature range. Charge collection and transmission electron microscopy were used to determine the onset of relaxation by directly imaging misfit dislocations and to investigate the variation in dislocation density with increasing anneal temperature. The strain variation in the epilayer was carefully monitored using double-crystal x-ray diffraction and Raman spectroscopy, and the annealing induced changes in strain related to the electron microscopy observed density of interface misfit dislocations. The relative merit of each experimental technique is discussed in the light of these results. The generation of strain relieving dislocations was found to be an activated process, with an activation energy on the order of 1.5 eV for the Si0.82Ge0.18 epilayer. Preferential surface streaking, along one of 〈110〉 directions, was observed in the relaxed samples despite a nondirectional uniform network of interface misfit dislocations.