Thesis (M.A.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / In this thesis, the optical constants of an atomically clean wafer of silicon have been determined by the analysis of elliptically polarized light produced by reflection of plane polarized light from the sample surface. First the theory of the reflection and transmission of plane polarized light at an interface between a dielectric and a conducting material is reviewed, and expressions relating the index of refraction n and the extinction coefficient K of the conductor to other physical parameters are derived. Then the production of elliptically polarized light by reflection at the interface is analyzed. Expressions are derived relating the optical constants of the conductor to the angle of incidence Φ, the azimuth of restored polarization Ψ, and a variable Δ which is related to the phase difference between the components of the elliptically polarized light. The operation of a Babinet compensator is discussed, and methods for determining Ψ and Δ are analyzed. The preparation of the silicon sample by grinding, chemical polishing, and heating to 1000°K in an ultra high vacuum is described. This method of preparation was chosen in order to produce an atomically clean surface for the reflection experiment. The method of obtaining data on Ψ and Δ with the aid of a Babinet compensator attached to a student spectroscope is described, and experimental problems encountered in the course of the measurements are discussed. Results of measurements on the silicon sample are recorded for four wavelengths, 6430 Å, 5890 Å, 5461 Å, and 4358 Å. At each wavelength, n and K are given for various angles of incidence, varying from 30° to 85°. Values of Ψ and of Δ are interpolated by graphical analysis to obtain Φ and ψ at each wave length, and these values are compared with those of other workers in the field. The values which were thus compared are the following: λ Φ ψ K n 6340 Å 75.25° 4.25° 0.14 3.76 5890 Å 76.50° 5.00° 0.17 4.10 5461 Å 77.00° 4.75° 0.16 4.27 4358 Å 78.50° 11.50° 0.41 4.53 / 2031-01-01

Thesis (Ph. D.)--California Institute of Technology, 1977. UM #77-11,886. / Advisor names found in the Acknowledgments pages of the thesis. Title from home page. Viewed 02/08/10. Includes bibliographical references.

Thesis--Helsingfors. / Bibliography: p. [50].

No description available.

Thesis--University of Helsinki.

Inaug.-Diss.--Uppsala.

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 217-219).

D.Sc.. / Please refer to full text to view abstract

Measurements are made on Si p - n junctions under reverse bias in the unstable avalanche breakdown region to determine the statistics of the current pulses, and their effect on the measured mean current - mean voltage characteristics. It is found that the slope and shape of the measured mean current - mean voltage is not unique, but depends on the external resistance in series with the power supply. The mean current - mean voltage characteristics are also found to display turnover, with the voltage at turnover and the magnitude of the maximum negative resistance both increasing with increasing resistance R. Measurements are also made to determine the relation between the current pulse amplitude I₁ and the voltage V₁ across the diode during the avalanche. The results show that over the range where data are available, a linear relation exists between reverse voltage and current pulse amplitude. The intersection of this line with the voltage axis is defined as the breakdown voltage V[subscript B], and its slope is the conductance denoted by g. A simple model consisting of a random switch in series with a two terminal device having the property that for V₁ < V[subscript B], I₁ = 0 and for V₁ > V[subscript B], I₁ = g(V₁- V[subscript B]) is proposed. An avalanche initiation transition probability which increases monotonically with increasing voltage in excess of V[subscript B], and an extinction transition probability which decreases monotonically with increasing excess voltage are postulated. The experimentally derived probability functions satisfy the chosen theoretical functional dependence on excess voltage to within experimental error. Assuming that the "switching" process is Markoffian, an expression for the fraction of the time during which the avalanche occurs is derived. Using this relation and the pulse amplitude data, a theoretical mean current - mean voltage characteristic is obtained which is in good agreement with the experimental curve. The predicted mean pulse rate curve is also experimentally verified. Illumination experiments show that the initiation transition probability is directly proportional to the number of carriers entering the avalanche region; the discharge probability for an electron entering the avalanche region is independent of illumination and carrier density in the breakdown region. The apparent predominance of a form of "surface leakage" in the reverse current makes it impossible to obtain data regarding the discharge probability per incoming electron from temperature variation experiments. Measurements of the spectral density of the current fluctuations over a wide range of frequency confirms the simple form S[subscript I](ω) = S[subscript I](0) / (1 + ω²τ²) associated with a Markoffian process. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The factors influencing the direct nitridation of silicon, including the effects of the native oxide layer covering the surface of silicon, the effects of hydrogen contained in the nitridation gas and the catalytic effects of metals added to the raw material silicon, were investigated, using a tubular flow reactor and a fluidized-bed reactor operated at temperatures ranging from 1150��C to 1390��C in a stream of nitrogen containing 10% hydrogen. The nitridation of silicon is not initiated until the native oxide is removed by an assistance of hydrogen contained in argon during the pretreatment or in the nitridation gas mixture. An induction period is observed before the initiation of the nitridation and depends on the nitridation temperature as well as the pretreatment time, which is associated with the removal of the oxide layer. The presence of hydrogen in the nitridation atmosphere is crucial for the nitridation of silicon. When pretreated silicon grains are exposed to nitrogen without hydrogen for a time period as short as 5 minutes, the subsequent nitridation, even with hydrogen, becomes extremely slow. The concentration of hydrogen as low as 0.3% is effective for sustaining the reactivity of silicon for the nitridation. The results suggest the formation of a protective layer on the surface of silicon when silicon grains are exposed to nitrogen without hydrogen. The protective film is suspected to be silicon oxynitride, or a mixture of silicon oxynitride and silicon dioxide or silicon nitride formed from the reaction of silicon with oxygen and nitrogen, depending on the temperature of its formation. However, the protective film does not form on the native oxide layer, and the reactivity of silicon is resumed upon the removal of the native oxide. An addition of calcium (as low as 0.125%) or yttrium (1.0-2.0%) to silicon suppresses the formation of ��-silicon nitride while iron enhances the formation of silicon nitride. Copper promotes not only the nitridation but also the formation of ��-silicon nitride at 1200��C, but enhances the ��-phase formation at higher temperatures. The role of liquid phases on the formation of ��-/��-silicon nitride was also discussed based on the nitridation of silicon impregnated with copper, calcium, silver, chromium and tungsten. / Graduation date: 2003