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We introduce a simple and fast iterative algorithm, named SCAOS (simple counterpropagation algorithm for optical signals), for simulating the counterpropagation of optical signals within a nonlinear fiber. Being based on the split-step Fourier method, the algorithm is easily implementable in many traditional optical simulators. Applications of the SCAOS algorithm to the vectorial nonlinear counterpropagation of a polarized pump and a probe signal demonstrate the phenomenon of lossless polarization attraction. The evolution of the signal polarization along the fiber, obtained by simulation, reveals that polarization attraction always entails a certain amount of degradation of the signal’s degree of polarization. Two different setups are studied, involving different types of fibers with Kerr nonlinearity, and highlighting the dependence of the attraction phenomenon, as well as of its effectiveness, on the fiber type.

Depth profiles of Si nanocrystals formed in sapphire by ion implantation and the effect of charging during X-ray Photoelectron Spectroscopy (XPS) and Secondary Ion Mass Spectrometry (SIMS) measurements have been studied. Atomic concentration and the chemical environment of Si, Al, and O have been measured as a function of depth from the sample surface by SIMS and XPS. Both as-implanted and annealed samples have been analyzed to understand the effect of nanocrystal formation on the depth distribution, chemical structure, and the charging effect before and after the formation process. SIMS measurements have revealed that the peak position of the Si concentration shifts to deeper values with implantation dose. This is explained by the fact that the structure of the matrix undergoes a phase transformation from pure sapphire to a Si rich amorphous Al2O3 with heavy dose implantation. Formation of Si nanocrystals has been observed by XPS by an increase in the Si-Si signal and a decrease in Si-O bond concentrations after the annealing. Variation in binding energies of Si and O with Si concentration (i.e., with depth) has been studied in terms of chemical environments and charging effects. It is found that binding energy of these elements shifts to lower values with increasing Si content. This is a result of less charging due to the presence of easy discharge paths in the Si rich regions of the matrix. Nanocrystal formation leads to even less charging which is probably due to the further increase in conductivity with the formation. [ABSTRACT FROM AUTHOR]

The behavior during annealing of low-energy As-implanted Si have been investigated by comparing secondary ion mass spectrometry (SIMS) and simulated profiles. Z-contrast scanning transmission electron microscopy (STEM) imaging has also been used to determine the As local distribution in proximity of the sample surface. The implants have been performed with energies between 1 and 10 keV both through a thermally grown 11 nm thick oxide and without any oxide mask. SIMS and STEM profiles show, after short annealing at 800–1000 °C, an As pileup in the first nanometers of the Si matrix in proximity of the SiO2/Si interface. We demonstrate that this phenomenon can be explained with a “Fickian” standard diffusion by assuming the presence of unspecified “dopant traps” near the SiO2/Si interface that cause a drastic reduction of the dopant able to diffuse inside the bulk. We have also verified that removing before annealing the superficial 4 nm of Si does not eliminate the As pileup. Different mechanisms proposed in literature to explain the uphill diffusion are discussed. Furthermore, the availability of a suitable simulation model allows us to evaluate the dopant diffusivity during the annealing and investigate the transient enhanced diffusion (TED) phenomena. [ABSTRACT FROM AUTHOR]

In this work we investigate the diffusion and the electrical activation of In atoms implanted into silicon with energies ranging from 40 to 360 keV and doses of 5 × 10[SUP12] and 5 ×10[SUP13]In/cm[SUP2] during rapid thermal processing. Our investigation shows a clear dependence of In outdiffusion and electrical activation on the implant depth. For a fixed dose, the electrical activation was found to increase with the implant energy. We propose that the data can be explained by considering the balance between the local In concentration and the C background. The occurrence of coupling between the C present in the substrate and the implanted In, depending on the C/In ratio, may in fact give rise to significant formation of C-In complexes. Such complexes play a role in the enhanced electrical activation due to the shallower level they introduce into the Si band gap (E[SUBν + 0.111 eV), with respect to the rather deep level (E[SUBν] + 0.156 eV) of In alone [R. Baron et al., Appl. Phys. Lett. 30, 594 (1977); R. Baron et al., ibid. 34, 257 (1979)]. The interaction of In atoms with the C background inside the silicon substrate has been, therefore, identified as the most likely origin of this behavior. In and C coimplantation has also been studied in this work, in order to further investigate the key role of C in the increase of electrical activation. A large increase of electrical activation has been detected in the coimplanted samples, up to a factor of about 8 after annealing at 900°C. However, C precipitation occurs at 1100°C, and has dramatic effects on the carrier concentration that falls by even two orders of magnitude. This limits the maximum thermal budget that can be used for In activation in C coimplanted material. [ABSTRACT FROM AUTHOR]