Maximum Ti concentrations in Si quantified with atom probe tomography (APT)

Atom Probe Tomography (APT) is used to explore Si into which a high concentration of Ti has been incorporated through ion implantation and pulsed laser melting. Ti shows abundant segregation out of the Si, with regions near the surface showing evidence of the classic “cellular breakdown” morphology characteristic of constitutional supercooling. Ti concentrations in excess of the nominal Mott limit have previously been reported, but these concentrations have relied on secondary ion mass spectrometry (SIMS) measurements, which are susceptible to artifacts. The APT method provides improvements over the SIMS method and shows that Ti concentrations are below the Mott limit everywhere outside of the broken-down regions below the surface SiO layer. The data confirm that Ti behaves as would be expected under a conventional rapid solidification theory. This has implications for how Ti in Si concentration data produced by non-atomistic techniques are interpreted and also indicates that the use of the conventional solidification apparatus can be used to predict Ti concentrations that may be achievable using implantation and laser melting techniques.