A preliminary study was made of the effect of the Ge content upon Sb diffusion in Si-rich Si1-xGex strained-layer heterostructures. It was found that the behavior of Sb was characterized by a higher diffusivity in the alloy than in Si. It was therefore deduced that there was a higher vacancy mobility and/or vacancy concentration in the alloy than in Si. It was proposed that, because B diffusion was reduced as the Ge content increased, it followed that B diffusion in this region did not occur mainly via vacancies. In the range of low Ge contents, the presence of Ge suppressed B diffusion whereas, at higher Ge contents, at least one report had shown that B diffusion became faster. By assuming that the vacancy concentration or mobility was greater at higher Ge contents, it could be deduced that B diffusion was dominated by an interstitial-based mechanism in the low-Ge range and by a vacancy mechanism in the high-Ge range. It was noted that such strained Si1-xGex layers were used to avoid dislocation short-circuit diffusion, but it remained an open question as to whether the strain itself affected Sb diffusion in the layers. The effect of compressive strain upon the vacancy parameters was unclear, but the reported effects of compressive strain upon interdiffusion did not indicate that strain could explain the present results. It was suggested that Sb could be used as a monitor, for dopant diffusion via vacancies, for comparison with other dopants.

A.D.N.Paine, M.Morooka, A.F.W.Willoughby, J.M.Bonar, P.Phillips, M.G.Dowsett, G.Cooke: Materials Science Forum, 1995, 196-201, 345-8