Dependence of critical thickness on growth temperature in GexSi1−x/Si superlattices

Abstract

We present direct evidence for the dependence of critical thickness on growth temperature in a lattice-mismatched epitaxial system. Ge0.5Si0.5/Si strained-layer superlattices have been grown by molecular beam epitaxy on (100) Si substrates at temperatures between 330 and 530 °C. The extent to which lattice mismatch is accommodated by elastic strain has been determined through x-ray diffraction, channeled Rutherford backscattering spectroscopy, and transmission electron microscopy. Lattice mismatch is found to be accommodated purely elastically in a structure grown at 365 °C. Samples grown at higher temperatures are seen to display increasingly high densities of misfit-accommodating dislocations. This growth-temperature dependence may account for apparent inconsistencies in critical thickness data reported in the literature. Our results clearly demonstrate the need to account adequately for the kinetics of defect formation in the prediction of critical thicknesses.