The formation of fluorine-vacancy complexes in strained Si-SiGe-Si multilayer structures and relaxed SiGe layers of varying Ge content was investigated using variable-energy positron annihilation spectroscopy, including Doppler-broadened spectra ratio curves. It was found that in all sample types there were two distinct regions defined only by the damage created by the implanted F ions. The first, shallower region (from the surface to a depth of ∼200nm) was found to contain a mixture of undecorated vacancies and fluorine-vacancy complexes; there was no correlation between the vacancy or F concentration in this region and the Ge content. The multi-layer samples might also have O contamination that was not present in the relaxed samples. The second region (at depths of 200 to 440nm) contained primarily fluorine-vacancy complexes in all samples. In the multi-layer samples secondary ion mass spectrometry results showed peaks of F accumulating in, or at the interfaces of, each SiGe multi-layer; the fluorine-vacancy complexes, however, were distributed over depths similar to those in the relaxed samples, with some localization at the SiGe layer located within the second region. The positron response was primarily to fluorine-vacancy complexes formed by the F implant in all samples. The F:FV ratios were approximately 3-7:1 in the relaxed samples. Positrons appeared to be relatively insensitive to the largest of the F secondary ion mass spectrometry peaks which lay beyond the second region. This was probably because the F had filled all the open volume at the SiGe layer, leaving no positron trapping sites.

Positron Annihilation Studies of Fluorine-Vacancy Complexes in Si and SiGe. C.J.Edwardson, P.G.Coleman, H.A.W.El Mubarek, A.S.Gandy: Journal of Applied Physics, 2012, 111[7], 073510