POINT DEFECT REDISTRIBUTION IN SI1-XGEX ALLOYS

Abstract

Using high resolution secondary ion mass spectrometry (SIMS) measurements we have studied the effects of germanium content on antimony diffusion in strained Si1−xGe x layers. Samples were molecular beam epitaxy (MBE) grown Si1−xGe x buried layers incorporating in situ doped antimony delta-layers. These were annealed for a variety of times and temperatures, following which SIMS profiles were taken and from these diffusivities were calculated. The results of a diffusivity versus germanium content study and a diffusivity versus time study are presented; equilibrium antimony diffusion coefficients in alloys of up to 30% germanium are given along with possible transient effects. Changes in antimony diffusivity with composition are attributed to changes in the vacancy population and the vacancy enthalpy of migration. Comparison with the diffusivity of boron versus germanium content in silicon-germanium alloys leads to the proposal that, in silicon-rich alloys, boron diffuses predominantly via the interstitialcy mechanism. The dependence of diffusivity on germanium content for boron is different from that of antimony and it is proposed that the boron diffusion mechanism changes from largely interstitialcy in silicon to vacancy in germanium—the change occurring at around 40% germanium.