Search

A simple numerical method based on finite differences to solve the scalar wave equation encountered in optical fibers is presented. The method uses the Ricatti transformation to the scalar wave equation and is capable of analyzing fibers of arbitrary refractive index profiles. Achieving errors as low as 0.005% for propagation constants is possible for lower-order modes. However, the error seems to increase for frequencies closer to cutoff.

The effects of doping on the electrical and optical properties of RF-sputtered a-Si/sub x/Ge/sub 1-x/:H (x=0.70) are investigated. The films were deposited at a constant substrate temperature of 200 degrees C, and n and p-doped samples were obtained by introducing controlled amounts of phosphine and diborane, respectively, in the sputtering atmosphere. The conductivity increased by about two orders of magnitude for the n-type samples and by one order of magnitude for the p-type samples. Thermoelectric power measurements confirmed that doping was achieved. The optical gap did not seem to vary upon doping. The presence of germanium and oxygen is responsible for an increase of the localized states in the gap and of the width of the conduction band tail states. Therefore, these films show less sensitivity to doping than those of a-Si:H deposited under similar conditions. A model for the density of states in the gap, which includes the effects of impurities (oxygen), , is presented in order to explain the observed results. >

Amorphous thin films of Si x Ge 1- x :H:O ( x = 0.70) were prepared by RF-sputtering at several substrate temperatures. The structural properties of these films were studied by IR spectroscopy and revealed features characteristic of hydrogen and/or oxygen bonded to silicon. The optical constants ( n, k ) were determined from reflection and transmission measurements at near-normal incidence for photon energies in the range of 1 and 2.6 eV. The optical gap was derived from the Tauc plot and correlated with the composition of the samples. The increase of hydrogen and/or oxygen decreases the value of refractive index and increases the optical gap. The room temperature DC conductivity can be reduced by as much as four orders of magnitude by combining the effects of hydrogen and oxygen compensation and for the concentrations used. The dependence of the conductivity on the atomic concentrations of hydrogen and/or oxygen follows a similar trend as the refractive index.

Hydrogen and fluorine incorporation in sputtered amorphous Si x Ge 1 − x and SiC films is described. Infrared and Raman spectroscopy is used to ascertain the amorphous nature of the films and to determine the amount of H and F incorporated and their nature of bonding. Incorporation of hydrogen or fluorine in the films is seen to increase with increasing partial pressure of hydrogen or fluorine. The identification of the different complexes present in the structure of these films and the assignment of different stretching, bending and/or wagging vibrational modes are discussed. Quantitative analysis of these spectra also reveal the relative preference of attachment by H or F to Ge, Si and C. Hydrogen and fluorine attach preferentially to Si and C for Si-Ge and SiC alloys respectively. H or F incorporated (− 40%) is much larger than the expected number of dangling bonds. However the number of states in the band gap steadily decreases with increasing H or F. Incorporation of H or F systematically increases the optical band gap and decreases the electrical conductivity. Hydrogen compensated SiC films are doped p or n types by incorporation of diborane or phosphine during sputtering. The atomic percentage of phosphorus and boron in the samples increases with increasing partial pressure of phosphine and diborane during deposition. The conductivity and thermoelectric power measurements are presented. These results show that doping has been achieved.

RF sputtered a-Si x Ge 1 − x ( x = 0.70) films have been deposited in an atmosphere of a mixture of Ar/NH 3 or Ar/NH 3 /H 2 at a constant substrate temperature of 200 °C. The IR spectra show the characteristic bands assigned to Si-N and Si-H vibrational modes. The N-H modes are present only for the samples prepared at high partial pressures of ammonia, and a shift of the Si-N and Si-H stretching bonds to higher frequencies is observed. The optical gap and absorption edge are also strongly dependent on nitrogen incorporation and the results are reported. Conductivity measurements are presented and they are seen to reflect the widening of the gap observed with nitrogen incorporation.

Doping of rf-sputtered a-SixGe1−x:H (x = 0.70) films at a constant substrate temperature of 200°C is investigated. Controlled amounts of phosphine and diborane enabled us to vary the conductivity by about two orders of magnitude for the n-type material and about one order of magnitude for p-type material. Thermoelectric power measurements confirmed that electrons and holes were predominant in the conduction process for phosphorus and boron doped samples, respectively. The optical gap does not change upon doping except in the case of high boron concentration (3 mTorr) for which a decrease of 0.05 eV is observed and an enhancement of absorption for lower energies can be detected.

Samples of ZBLA and HBLA glasses were subjected to various fluences of neutron irradiation, and the spectral dependence of optical absorption was measured before and after irradiation. The IR edge was found to be unaffected by neutron irradiation for the fluences used. However, a red shift occurred at the UV edge which slightly recovered after three weeks.