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Measuring with a spectroscopic ellipsometer (SE) in the 1.845 eV photon energy region we determined the complex dielectric function (E = e1 + ieZ> of different kinds of amorphous silicon prepared by self-implantation and thermal relaxation (500 "C, 3 h) . These measurements show that the complex dielectric function (and thus the complex refractive index) of implanted a-Si (i-a-Si) differs from that of relaxed (annealed) a-Si (r-a-Si) . Moreover, its E differs from the E of evaporated a-Si (e-a-Si) found in the handbooks as E for a-Si. If we use this E to evaluate SE measurements of ion implanted silicon then the fit is very poor. We deduced the optical band gap of these materials using the Davis-Mott plot based on the relation: (E&'>~'~ -(E -E8). The results are: 0.85 eV (i-a-Si), 1.12 eV (e-a-Si), 1.30 eV (r-a-Si) . We attribute the optical change to annihilation of point defects.Understanding the structure and properties of amorphous silicon (a-Si) is a scientific challenge of some complexity.' The problem is that there is not a single type of a-Si. There are several measurements which indicate that the properties of implanted amorphous silicon (i-&i) differ significantly from those of well relaxed (annealed) a-Si (r-u-Si) .&' Additionally, we must know the optical constants of different kinds of a-Si to evaluate well the optical measurements. Earlier measurements' showed that the E (complex dielectric function, c = e1 + ieZ) of i-&i and r-a-Si differ from the E of evaporated a-Si (e-a-Si) found in the handbooks as E for aSi.' If we use this E to evaluate spectroscopic ellipsometric (SE) measurements of ion implanted silicon then the fit is very poor.' A similar thing is described by McMarr" and Vedam, McMarr, and Narayan" who also measured self-implanted fully amorphous silicon and tried to evaluate the spectra modeling the sample as a mixture of voids and a-Si prepared by low-pressure chemical vapor deposition (LPCVD) . l2 The model calculations resulted in a surprising -9% void fraction. This fact also indicates that the E of LPCVD a-Si must not be used for i-a-Si.For the experiments Wacker made, p-type Si (100) wafers of 4-8 Sz cm resistivity were implanted with Si ions at room temperature. The implantation conditions are shown in Table I. After implantation an adequate plasma stripping procedure13 was applied to remove a possible hydrocarbon deposition. The SE measurements were followed by annealing (500 "C, 3 h, N2 ambient) to achieve the well relaxed state.2'3'7 (Well relaxed means that longer or higher temperature annealing does not change the optical properties of the layer.)The ellipsometric measurements were performed with a rotating analyzer type ellipsometer in the 270-700 nm wavelength (4.6-1.8 eV photon energy) region at 70", 73", and 75" angle of incidence at the Twente Technical University. From these multiple-angle-of-incidence measurements we could take into account the thickness of the native oxide. The measurement error increased at the red end of the spectrum because of the light source (...

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Porous silicon layers were prepared by electrochemical etching of p-type single-crystal Si (c-Si) of varying dopant concentration resulting in gradually changing morphology and nanocrystal (wall) sizes in the range of 2–25nm. We used the model dielectric function (MDF) of Adachi to characterize these porous silicon thin films of systematically changing nanocrystal size. In the optical model both the surface and interface roughnesses have to be taken into account, and the E0, E1, and E2 critical point (CP) features are all described by a combination of several lineshapes (two-dimensional CP, excitonic, damped harmonic oscillator). This results in using numerous parameters, so the number of fitted parameters were reduced by parameter coupling and neglecting insensitive parameters. Because of the large number of fitted parameters, cross correlations have to be investigated thoroughly. The broadening parameters of the interband transitions in the measured photon energy range correlate with the long-range order in the crystal. The advantage of this method over the robust and simple effective medium approximation (EMA) using a composition of voids and c-Si with a nanocrystalline Si reference [Petrik et al., Appl. Surf. Sci. 253, 200 (2006)] is that the combined EMA+MDF multilayer method of this work provides a more detailed description of the material and layer structure.

Erbium-doped tellurite glasses are of great interest for the fabrication of active integrated circuits because of their unique properties in terms of bandwidth and rare earth solubility. The fabrication of multimode channel waveguides in a glass of this family, namely, a sodium-tungsten-tellurite glass, is demonstrated using a high-energy ion beam irradiation technique. Nitrogen ions with dose of 1.0×1016ions∕cm2 and 1.5MeV energy were used for this aim. The waveguiding effect was investigated using the end-fire coupling technique.