Effect of film thickness on hydrogen content in a-Si : H

The hydrogen content, its depth distribution, and its bonding configuration have been studied in hydrogenated amorphous silicon prepared by plasma-enhanced chemical vapor deposition with hydrogen-diluted silane. Nuclear reaction analysis and infrared spectroscopy were used to determine the total amount of hydrogen and its bonded component, respectively. It has been established that the total concentration of hydrogen does not depend on the film thickness, and has a uniform depth profile. The concentration of bonded hydrogen changes with the film thickness within the measurement accuracy. The data obtained suggest the presence of molecular (non-bonded) hydrogen, uniformly distributed in concentration across the film thickness.     

a-Si:H thin film microstructure influenced by HOMOCVD-process parameters

Hydrogenated amorphous silicon films prepared by homogeneous chemical vapor deposition (HOMOCVD) process were studied with respect to their microstructure by field-assisted ion exchange (FAIE) techniques. Results concerning the influence of HOMOCVD process parameters such as temperature, gas pressure, flow and substrate temperature are presented. Two series of deposition experiments were carried out: at constant gas phase conditions and at the variable ones. The obtained results showed that the amount of micropores was not determined by the growth rate. This inference is in contrast with the results obtained for plasma CVD a-Si:H. On the basis of the presented results it is possible to choose the deposition conditions, which yield a-Si:H films with the lowest micropore density.     

Raman study of ion-implanted hydrogenated amorphous silicon

The effect of silicon and hydrogen ion implantations on the structural properties of hydrogenated amorphous silicon films was studied by means of Raman spectroscopy, with the aim of revealing the influence of hydrogen atoms inserted into the silicon matrix on its short-range order. To separate the implantation-induced increase in the structural disorder from the effect of the implanted hydrogen, the implantation doses of silicon and hydrogen ions were selected to create closely similar numbers of host-atom displacements. The results obtained suggest that the presence of hydrogen in amorphous silicon reduces the structural disorder related to variations in the silicon bond length, but affect the bond-angle deviations to a lesser extent.     

a-Si:H film on side-polished fiber as optical polarizer and narrow-band filter

An optical waveguide structure consisting of side-polished single-mode fiber covered with thin a-Si:H planar waveguide is studied as a channel-dropping narrow-band filter and fiber-optic polarizer. Spectral and polarization characteristics of the structure are measured in the wavelength region of 600–1600 nm, for the different values of the a-Si:H film thickness and the superstrate refractive index. The FWHM of the filter is about 8 nm for the asymmetric waveguide and 10 nm for the symmetric one. The discrimination of the resonance minima for two polarizations varies from several tens for the symmetric PWG up to several hundreds of nanometers for the asymmetric PWG. The optical losses in the off-resonance region are less than 0.3 dB. The measured value of the extinction coefficient of the fiber-optical polarizer is 32.5 dB.     

One-step field-assisted ion exchange for fabrication of buried multimode optical strip waveguides

A method for one-step field-assisted silver-sodium ion exchange is proposed for the preparation of buried multimode optical strip waveguides in glass. Silver ions were supplied by a silver strip. A sodium nitrate melt was used as the anode, as well as for waveguide burial. The method provides good control over the waveguide cross-section.     

Optical and structural characterization of Z-cut LiNbO/sub 3/ optical waveguides formed in a mixed proton source

In this paper, the optical and structural characteristics of Z-cut LiNbO/sub 3/ optical waveguides are experimentally investigated. The waveguides have been fabricated by fully immersing the samples in a closed beaker containing a mixture of benzoic and adipic acid at different concentration ratio. The influence of the dilution ratio on crystallographic phases, wavelength dispersion, diffusion coefficient, and index profile has been determined by using infrared absorption spectroscopy and optical characterization. The control of the thickness of guiding layers corresponding to /spl beta//sub 1/ and /spl beta//sub 2/ phases can be realized by varying the dilution ratio of the melt.     

Effect of keV ion irradiation on mechanical properties of hydrogenated amorphous silicon

The susceptibility of mechanical properties of hydrogenated amorphous silicon (a-Si:H) to the implantation-enhanced disorder has been studied with the aim to extend the application field of this material in the technology of micro-electromechanical systems. Effect of keV ion irradiation on the elastic modulus, E, of hardness, H, and of root-mean-squared roughness to silicon ion implantation has been determined. The mechanical properties were evaluated by nanoindentation testing. E of 119 GPa and H of 12.3 GPa were determined for the as-prepared a-Si:H film. The implantation of silicon ions leads to a decrease in E and H, evaluated for a series of the implantation fluences in the range of 1.0 × 10¹³–5.0 × 10¹⁶ cm^?2. Surface smoothing has been observed at high fluences and low ion energy of 18 keV, suggesting that ion beam may be used as a tool to reduce the roughness of the a-Si:H surface, while keeping intact the mechanical properties inside the film. The conducted experiments show that it is possible to prepare a-Si:H films with hardness and smoothness comparable to crystalline silicon.     

Method of refractive index profile reconstruction from effectiveindex of planar optical monomode waveguides: Application to potassiumion-exchanged waveguides

A simple nondestructive method for determination of refractive index profile of single-mode waveguides using the measured effective refractive indexes is proposed. The method is based on the extraction of the additional data about the waveguide profile from the investigation of its evolution with the duration of fabrication process. The profile reconstructions are carried out using an appropriate algorithm in the frames of the WKB approximation. The method is applied for few- and single-mode waveguides, obtained by K⁺-Na⁺ field assisted ion exchange. The results are corroborated with the reconstruction from the effective refractive indexes measured at a shorter wavelength, as well as with profile study by means of step-by-step etching