A new technique is described by which ionic species can be rapidly transported into oxide films, and once there provide effective and stable field effect passivation to silicon surfaces. Field effect passivation in thermally grown oxide films has been achieved by embedding potassium ions using a combined drift and diffusion mechanism at high temperature. This process has been shown to be over 10 times faster than a pure diffusion process. The resulting passivation stable for periods exceeding 600 days, with lifetimes reaching 1.4 ms, equivalent to a surface recombination velocity (SRV) ≤ 5.7 cm/s, on 1 Ωcm, n-type, FZ-Si.
Cation diffusion is an important rate-limiting process in the growth of pyrrhotite (Fe1-xS) in passivating films on steels exposed to sulfidic environments, and for proposed synthetic applications of Fe1-xS, for example single-phase magnetic switching devices. Above the Néel temperature TN of 315 °C, where Fe1-xS is paramagnetic and structurally disordered, iron self-diffusivity *DFe predictably follows a standard, established Arrhenius law with temperature. However, we report (57)Fe tracer diffusion measurements below TN, obtained using secondary ion mass spectrometry (SIMS), that demonstrate a 100-fold reduction in diffusion coefficient as compared to the extrapolated, paramagnetic Arrhenius trend at 150 °C. The results can be described by a magnetic diffusion anomaly, where the vacancy migration energy for the spontaneously-magnetized cation sublattice is increased by approximately 40% over the paramagnetic state. These constitute the first set of consistent diffusivity data obtained in magnetic pyrrhotite, allowing more accurate prediction of pyrrhotite growth rates and determination of magnetic properties for synthetic devices.
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