A quantitative study of compositional profiles of chemical vapour-deposited strained silicon-germanium/silicon layers by transmission electron microscopy

The chemical composition across strained silicon-germanium/silicon layers has been studied quantitatively using a variety of analytical electron microscopy techniques: energy-dispersive X-ray microanalysis (EDX), electron energy-loss spectroscopy (EELS), high-angle annular dark-field imaging (HAADF) and high-resolution electron microscopy (HREM). The results from these different techniques are compared. EELS and HAADF in particular are shown to be powerful methods to calculate compositional profiles from which growth information can be extracted. It is shown that the activation energy for interdiffusion of strained SiGe/Si layers is 2.3 +/- 0.3 eV, which is significantly lower than for the diffusion in bulk Si or bulk SiGe. The measured interface widths are much larger than predicted using a two-state exchange model suggesting that this model is an oversimplification. Increasing the growth temperature in chemical vapour deposition broadens SiGe/Si interfaces asymmetrically: the SiGe-on-Si interface is broadened much more than the Si-on-SiGe interface. Growth interrupts lead to Ge depletion. The growth rate of SiGe is reduced when the germane flow commences and reaches a steady-state condition only for layers wider than 10 nm. These results can be explained by hydrogen passivation of the growth surface. (C) 1999 Elsevier Science B.V. All rights reserved.