Volume 34, Issue 6, 01 June 1963

Influence of Vacuum Conditions on Epitaxially Grown Permalloy Films
View Description Hide DescriptionPermalloyfilms (83 wt% Ni‐17 wt% Fe) epitaxially grown on (100) NaCl were examined in the electron microscope before and after beam annealing. An ultra‐high vacuum system with an ultimate vacuum of 10^{−10} Torr and a vacuum system with an ultimate vacuum of 10^{−6} Torr were used for the evaporation. Films at 10^{−5} Torr were prepared in both systems to rule out the influence of the vacuum system on the films. Evaporation rates were adjusted to either 30 Å/sec or 14 Å/min. Electron micrographs and electron diffraction patterns showed that the films ranged from polycrystalline for films evaporated at 30 Å/sec and 10^{−5} Torr to single crystalline with grains of several millimeters diameter for films evaporated at 30 Å/sec and 10^{−9} Torr. The crystallographic misorientation varied widely in films which were partially single crystalline and amounted to only a few degrees over areas up to ⅛‐in. diameter for films which exhibited perfect single‐crystal electron diffraction patterns.

Avalanche Effects in Silicon p—n Junctions. I. Localized Photomultiplication Studies on Microplasmas
View Description Hide DescriptionAn improved experimental technique is described for the investigation of carrier multiplication in very small areas, particularly microplasmas. A light spot of a few microns diameter is positioned to cover a microplasma of comparable or smaller size and the multiplied photocurrent is measured as a function of reverse voltage.
When the size of the microplasma is much smaller than the light spot, then the multiplication as a function of voltage is dependent upon the characteristics of the microplasma in an upper voltage range just below the microplasma breakdown voltage. In a lower voltage range the microplasma has negligible effect on multiplication. By comparing for the upper and lower voltage ranges the behavior of the reciprocal of the multiplication factor as a function of voltage, it is possible to determine that the diameters of the area of the microplasma regions vary from less than one to more than 5 μ.
Multiplication factors as high as 10^{6} were measured. At high multiplication (M>100), a deviation from the theoretically expected linear dependence of 1/M vs V is observed. This deviation can be described by two effects: (1) the influence of the space charge of the multiplied carriers and (2) the pulsing mechanism of the microplasma. Because of this deviation, microplasma diameters of less than 1 μ cannot be accurately determined.
Another consequence of the pulsing effect is an apparent negative resistance in the V—Icharacteristic of a diode containing a microplasma. Dependence of the apparent negative resistance on load resistance, shunting capacity, and light intensity was investigated, and can be explained with the pulse model.

Avalanche Effects in Silicon p—n Junctions. II. Structurally Perfect Junctions
View Description Hide DescriptionThe fabrication of a planar guard ring diode which exhibits uniform microplasma‐free breakdown is described. Discrepancies are discussed between the behavior of these junctions and those reported by Batdorf et al. and Chynoweth, including results showing extremely hard V‐I characteristics associated with uniform avalanche breakdown. Experimental evidence is presented which confirms Shockley's theory in which the breakdown behavior is predicted from the Poisson distribution of impurities within the space‐charge layer. The photomultiplication technique as described in Paper I is applied to uniform p—n junctions. The linearity of 1/M vs V, as predicted by theory, was verified for values of M between 1.6 and 500. For higher values, the multiplication curves deviate from a straight line. In this higher range they are in good agreement with the pulse‐multiplication model developed in Paper I. Light emission patterns from these junctions are shown and a correlation between these patterns and crystal properties is discussed. The effects of resistivity striations in the siliconsingle crystals is shown to have a strong effect on breakdown areas and no effects of dislocations and oxygen on uniformity are found. From capacity and multiplication measurements a value for the breakdown field of E_{B} =445±25 kV/cm was obtained for a 32‐V junction.

DC Electroluminescence in Thin Films of ZnS
View Description Hide DescriptionElectroluminescent thin films of the composition ZnS:Cu,Mn,Cl, which are capable of dc excitation, are examined for their optical, chemical, and electrical properties. The emission is dominated by electronic and ionic processes occurring at the anode. A model is proposed for the excitation mechanism which is based on hole injection across a heterojunction composed of ZnS and a copper‐rich phase. The mechanism explains emission at lower‐than‐band‐gap voltages. The spectrum of the yellow emission of Mn in these films is composed of two closely spaced emission bands and is, therefore, different from the known yellow emission from Mn in ZnSphosphors.

Microwave Frequency Multiplication by Hot Electrons
View Description Hide DescriptionAn experimental study is made of microwave frequency multiplication observed in germanium at power levels of several kW. Using a fundamental frequency of 9.4 Gc/sec, a third harmonic yield of about 1% was found. The data agree with calculations based on the observed deviations from Ohm's law. The anisotropy and the high frequency limit of the multiplication are calculated.

Influence of Ion Reflection Probability on Potential Distribution in Low‐Pressure Thermionic Converters
View Description Hide DescriptionSome numerical results are presented as an example to show how, for certain boundary conditions, the voltage—current characteristic in low‐pressure large‐spaced gas diodes may give the appearance of saturating at a value of output current which is less than the saturated electron current from the emitter. The crucial parameter introduced which is mainly responsible for the phenomenon is f, defined as the probability that a returning ion reflects again as an ion after colliding with the emitter.

Theory of Laser Regeneration Switching
View Description Hide DescriptionThe theory of laser regeneration switching is developed. The rate equations are derived and, using ruby as an example, the material‐cavity parameters are evaluated for a 1‐cm^{3} rod. Steady‐state solutions for t<0 are given, and the equations formally integrated for t>0. Using approximate solutions, three modes of laser operation, other than the normal mode, are discussed. With the first mode: the pulsed reflection mode (PRM) switched to minimum coupling, output pulses with peak powers of 17 MW and 10 nsec duration are predicted, with 2% of the initially stored energy emitted. With the second mode: the PRM switched to critical coupling, peak powers of 170 MW with pulse durations of about 8 nsec, and with about 50% of the stored energy emitted, are predicted. In the third mode: the pulsed transmission mode (PTM), peak powers of about 900 MW, pulse durations around one nsec, with 52% of the stored energy emitted, are predicted. Experimental approaches to PTM operation are briefly discussed.

Interaction between a Dielectric (or Cold Plasma) and a Cavity
View Description Hide DescriptionThis paper treats the interaction between a cylindrical plasma column (or dielectric material) and a resonant cavity from which it protrudes. From the results, one may determine the dielectric constant and loss, or in the case of a plasma, the plasma frequency and collision frequency, given measured values of the resonant frequency shift and change in the cavityQ. This theory differs from earlier theory on cylindrical cavities in that it treatsacavity of more general shape, although restricted to TM modes, and takes into account the subtle boundary effects at the openings through which the plasma is admitted. These effects may be calculated by estimating the field variation over the part of the cylindrical plasma surface that lies inside the cavity.

Coupling of Electromagnetic and Magnetostatic Modes in Ferrite‐Loaded Cavity Resonators
View Description Hide DescriptionA formalism is developed for treating the coupling of electromagnetic and magnetostatic modes in ferrite‐loaded cavityresonators. Coupled‐field equations are obtained by separating the magnetic field into rotational and irrotational parts. The fields are then expanded in terms of electromagnetic modes and magnetostatic modes, leading to coupled equations for the mode amplitudes. From these equations, one may evaluate the detuning and mode splitting resulting from the interaction of the ferrite with the cavity fields. In this treatment, there is no limitation as to the size of the ferrite sample, and the effects of wall proximity and the dielectric properties of the ferrite are specifically included.

On Strain‐Enhanced Diffusion in Metals. I. Point Defect Models
View Description Hide DescriptionPlastic deformation may affect bulk diffusion by altering the rates of point defect production and annihilation. In the present work (Part I) a detailed analysis of this phenomenon is given with particular emphasis upon possible upper limits for the magnitude of the effect at elevated diffusion temperatures where bulk diffusion occurs over macroscopic distances. In order to consider all possibilities from this point of view the following three models are analyzed: model I—vacancies may be created or destroyed at jogs on gliding screw dislocations and climbing edge dislocations. These possible vacancy sources and sinks are intermixed within crystal subgrains and the net source or sink action is zero over representative subgrain volumes; model II—a net vacancy source (or sink) action is required within the subgrains in order to support the required nonconservative dislocation motion. The required excess vacancies are destroyed (created) at the subgrain boundaries where the concentration is maintained in equilibrium; model III—large numbers of vacancies are readily created everywhere during deformation but are destroyed everywhere in the specimen volume only with difficulty. It is concluded that model I is probably the most realistic. In this case, upper limits are obtained for the required defect production and destruction at dislocations, and it is found that the required defects can be obtained from rather small perturbations of the usual thermally generated fluxes in detailed balance at the jogs. At practical diffusion temperatures and strain rates of the effects of the deformation on bulk diffusion are, therefore, very small and are below the limits of detection by usual methods. Model II appears to be conceivable under certain conditions. Analysis of this case indicates that the effects of deformation are larger than in model I because of the longer range vacancydiffusion which is required. However, the effects are still small under usual conditions. Model III is purely phenomenological and is included since it has been used by others. Several characteristics of this model which may be used to set limitations on possible enhancements obtainable in this model are derived. In addition to the analysis of the above three models, detailed discussion is given of the following aspects of the diffusion—deformation problem: (1) effect of surface vacancy sinks on diffusion—deformation experiments carried out near a free surface; (2) diffusion enhancement expressed in terms of the number of excess vacancy jumps; (3) temperature dependence of the diffusional effects of deformation; (4) mechanical work required to maintain nonequilibrium vacancy concentrations; (5) the relationship between macroscopic creep behavior and nonequilibrium vacancies; (6) the possibilities of interstitial production. Many of the results established here are employed in Part III [J. Appl. Phys. (to be published)] where a comprehensive interpretation of recent experimental work in this field is carried out. Part II [J. Appl. Phys. (to be published)] consists of an analysis of strain‐enhanced diffusion due to short‐circuiting along static and moving dislocations and grain boundaries.

Minority Carrier Thermoelectric Cooling
View Description Hide DescriptionThe fallacy in a recently proposed theory of minority carrier cooling is pointed out. The correct approach is given and the current literature on the subject is summarized. It is emphasized that cooling devices utilizing minority carrier effects are normally less efficient than conventional thermocouple modules.

An Anomalous Dissipation Factor Maximum in Sapphire
View Description Hide DescriptionThe temperature and frequency dependencies of the dielectric properties of sapphire were determined by guarded measurements within the ranges −160° to 400°C and 10^{2} to 10^{4} cps. A broad dissipation factor maximum, exhibiting apparently anomalous behavior, was observed. Although the frequency at which the maximum occurred was exponentially temperature‐dependent, activation energy values calculated on the basis of a dipolar relaxation model varied reversibly between 0.2 and 0.5 eV as a function of vacuum heat treatment at 400°C and of exposure to dry hydrogen, dry oxygen, or moist air. The dissipation factor behavior which would result from two alternative mechanisms, interfacial polarization and resonance, is discussed briefly on the basis of the possible existence of variable conductivity surface layers and the possible presence of hydrogen in the vicinity of dislocations.

Polynomial Approximation to Focal Constants of Equidiameter Two‐Cylinder Lenses
View Description Hide DescriptionThe approximate polynomials to the focal constants of equidiameter coaxial two‐cylinder lenses are given by making use of the methods which are used to approximate elementary functions for computer applications. The range of voltage ratio Φ_{2}/Φ_{1} of two cylinders are taken as 1/20≲Φ_{2}/Φ_{1}≲20. The polynomials obtained by Chebyshev expansions are better than those obtained by Taylor expansions. The convergence of the expansion depends greatly on the choice of the expansion parameters (arguments) as well as on its range. The polynomials of the 8th degree, obtained from the partial sums of Chebyshev expansions with the parameter x=½ log(Φ_{2}/Φ_{1}), give smaller relative errors than 2×10^{−4} in the above range for the focal constants of the lenses with typical axial potentials.

Injection Electroluminescence in Gallium Antimonide
View Description Hide DescriptionEmission of high‐intensity infrared radiation at 1.6 μ has been observed from forward‐biased GaSb p‐n junctions. Visual inspection indicates that the radiation is coming from the junction or close proximity to it. Optical pumping of the base material produces the same spectrum of radiation as p‐n junction injection. Lack of significant line shift in both absorption measurements and measurements in magnetic fields up to 90 000 G indicates that the radiation is not produced by band‐to‐band transitions, but is probably connected with impurities. Further evidence that the transitions are via an impurity level is obtained from the fact that the radiation spectrum is changed by the addition of a different impurity.

Boron‐Induced Microstrains in Dislocation‐Free Silicon Crystals
View Description Hide DescriptionDislocation‐free silicon crystals, Czochralski‐grown and solution‐doped with boron, have been investigated by x‐ray diffraction microscopy. The x‐ray measurements indicate that the perfection of dislocation‐free crystals can be less than that of crystals of finite dislocation density. Microstrains were found to be the dominating imperfection. Large‐area topographs show diffraction contrast which is strongly reflection dependent. The topographs clearly show the presence of inhomogeneous strains confined to localized lines and planes but extending over the whole crystal cross section. The x‐ray measurements suggest that boron‐doped silicon contains numerous precipitates which act as strain centers. The precipitates lie on {111} planes and produce a strong warping and bending of the lattice planes.

Probe Noise in Different Regions of a Gas Discharge
View Description Hide DescriptionNoise flowing to shielded probes in neon gas discharges is measured in the various regions of the discharge between 0.55 and 30 Mc under floating probe conditions. There is a low‐frequency noise mechanism that is most pronounced in the negative glow region, a high‐frequency noise mechanism that is most pronounced in the positive column but absent in the negative glow region, and a shot noise mechanism that predominates around 4 Mc. The shot noise under floating probe conditions gives a qualitative measure for the carrier density distribution in the discharge. The equivalent noise temperature can be smaller than the electron temperature; in the negative glow region this is caused by the space‐charge suppression of the ion shot noise, but in the positive column the low noise temperature of the high‐frequency noise mechanism is also an important factor. The high‐frequency noise temperature is much smaller than for unshielded probes.

Paramagnetism and Lattice Spacings of Some Cerium‐Rich Cerium—Europium Alloys
View Description Hide DescriptionParamagnetic susceptibility of cerium‐rich cerium‐europium alloys has been studied from 300° to 1050°K. These measurements indicate that the electronic structure of the localized 4f‐electrons of europium atoms in solid solution with cerium is very much the same as in europium metal. This finding is supported by the lattice parameter measurements on these alloys at 298°K. The solubility limit of europium in cerium is found to be at 4.6 at.% europium at about 800°K.

Secondary‐Electron‐Emission Phase‐Angle Distributions in High‐Frequency Multipacting Discharges
View Description Hide DescriptionNumerical calculations of emission phase‐angle distributions of electrons in a low‐pressure, high‐frequency (multipacting) electric discharge have been carried out on a Burroughs 220 digital computer. An integral equation for the phase‐angle distribution is developed, and the numerical techniques used for its solution are outlined. The distribution of multipacting electrons with respect to the parameter v/v _{0}, the ratio of impact velocity to emission velocity, has been calculated for several situations. These distributions show distinctive peaks which explain the success of the assumption v/v _{0}=constant, used by previous workers, in predicting the breakdown region.

A Model for Boundary Diffusion Controlled Creep in Polycrystalline Materials
View Description Hide DescriptionThe creep rate (ė) predicted by the boundary diffusion (D_{b} ) model is , where σ is the stress, W is the boundary width, (GS) is the average grain size, and Ω is vacancy volume. The stress dependence is the same as the lattice diffusionmodel, given by C. Herring, while the grain size dependence and the numerical constant are greater for boundary diffusion. Discussion of the mechanism of creep in polycrystalline alumina is based on the differences between the lattice and boundary diffusionmodels.

Linewidth and Temperature Shift of the R Lines in Ruby
View Description Hide DescriptionImproved experimental data have been obtained between 20° and 350°K for the widths and temperature shifts of the R lines in ruby. Above 77°K the results can be accurately described in terms of Raman scattering of Debye‐model phonons. There is no evidence for measurable contributions to the widths and shifts from direct processes involving emission or absorption of a single resonant phonon. Below 77°K the principal contributions are from crystal inhomogeneities.