In this Letter we investigate boron diffusion as a function of the Fermi-level position in crystalline silicon using ab initio calculations. Based on our results, a new mechanism for B diffusion mediated by Si self-interstitials is proposed. Rather than kick out of B into a mobile channel, we find a direct diffusion mechanism for the boron-interstitial pair for all Fermi-level positions. Our activation energy of 3.5 3.8 eV, migration barrier of 0.4 0.7 eV, and diffusion-length exponent of 20.6 to 20.2 eV are in excellent agreement with experiment.

We report on an erbium cascade laser in a fluorozirconate fiber. Lasing on the transition 4I11/2→4I13/2 at 2.71 μm is supported by colasing on the transition 4S3/2→4I9/2 at 1.72 μm. This recycles the excitation that is lost via excited-state absorption and avoids the saturation of the output power. Threshold at 2.71 μm is 33 mW launched pump power at 791 nm. The measured slope efficiency of 22.6% is relatively close to the 29.1% stokes-efficiency limit. An output power of 158 mW is obtained, limited only by the 1.43 W power available from the Ti: sapphire pump laser. Output power is 15 and slope efficiency 2.5 times higher than reported in previous publications.

We present a kinetic lattice Monte Carlo study of the behavior of a dopant flux driven by a vacancy gradient, associated with the diffusion of substitutional impurities via a vacancy mechanism in silicon. Recent ab initio results are used for a quantitative description of the impurity-vacancy interaction. We find a dopant flux smaller than, but in the same direction as, that predicted by the pair diffusion model, with the deviation greatest at high temperatures.

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