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1 Oct 1968

Volume 39, Issue 11, pp. 4877-5346

Page 1 of 3 Pages Return to All Sections Next Page
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A Model for Magnetic Instabilities in Hard Superconductors: The Adiabatic Critical State

P. S. Swartz and C. P. Bean

J. Appl. Phys. 39, 4991 (1968); http://dx.doi.org/10.1063/1.1655898 (8 pages) | Cited 92 times

Online Publication Date: 19 November 2003

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The isothermal critical‐state model of hard superconductors is extended to include the effects of heating when the applied field is changed suddenly and magnetic flux enters adiabatically into the bulk. We consider the following specific situation. A semi‐infinite slab of superconductor is cooled in a magnetic field lying in its surface plane. Next, the external field is raised isothermally by an amount Hs. This excess field decreases linearly to a depth δ= 10Hs∕4πJc from the surface. Finally, the field is raised by an infinitesimal amount ΔH in a time short compared to the thermal diffusion time and long compared to the electromagnetic diffusion time. Each element of volume exposed to the changing field receives a thermal impulse proportional to the local‐flux‐change times Jc. This thermal impulse, in turn, lowers the critical current and allows more flux to penetrate. We find that if Hs exceeds some critical value Hfj, then the isothermal critical state is not the only allowed state of the superconductor. This instability field is given in terms of the critical current density Jc, derivative of the critical current density with temperature, ∂Jc∕∂T, and the volume specific heat C by the formula Hfj= [−π3CJc∕(∂Jc∕∂T)]1∕2. The application of the incremental field ΔH can initiate an avalanching process, or a flux jump, that terminates in an adiabatic critical state. Immediately following the flux jump the internal field, the induced supercurrent, and the temperature rise at each position are associated in a self‐consistent way with the avalanche of flux that has entered the superconductor. In this framework a flux jump is viewed as a switching from the isothermal critical state to an adiabatic critical state. The magnitude of the jump is related to Js and is calculated.

Local‐Mode Absorption and Defects in Compensated Silicon‐Doped Gallium Arsenide

W. G. Spitzer and W. Allred

J. Appl. Phys. 39, 4999 (1968); http://dx.doi.org/10.1063/1.1655899 (11 pages) | Cited 58 times

Online Publication Date: 19 November 2003

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Silicon is known to be an amphoteric impurity in GaAs. A large number of ir absorption bands have been previously reported for Si‐doped GaAs which has been compensated by Li or Cu diffusion. These bands, which are at frequencies above the pure GaAs single‐phonon spectrum, have been attributed to localized vibration modes of defects. The present experimental study extends previous work to show that all the observed bands (frequencies given in parentheses) are explicable in terms of the presence of the following defects: SiGa (384 cm−1), SiAs (399 cm−1) SiGa‐LiGa (374, 379, 405, 470, 480, 487 cm−1), SiGa‐CuGa (374, 376, 399 cm−1), and SiGa‐SiAs. (367, 393, 464 cm−1). These assignments appears to be consistent with results obtained by varying the Si concentration and by different thermal treatments.

Profile Measurements of Plasma Columns using Microwave Resonant Cavities

Michael A. W. Vlachos and Hulbert C. S. Hsuan

J. Appl. Phys. 39, 5009 (1968); http://dx.doi.org/10.1063/1.1655915 (5 pages) | Cited 8 times

Online Publication Date: 19 November 2003

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The density profile of a positive column of a gas discharge is measured by the comparison of two microwave cavity measurements. The two cavity modes used are the TE011 and TM020.

Measurement of Plasma Electron Distributions using Microwave Cavities

C. J. Burkley and M. C. Sexton

J. Appl. Phys. 39, 5013 (1968); http://dx.doi.org/10.1063/1.1655916 (4 pages) | Cited 9 times

Online Publication Date: 19 November 2003

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A new technique is presented whereby electron radial distributions in the positive column of a mercury plasma were determined using simultaneous measurements from TM020 and TE011 microwave cavities. Experimental results are compared with a comprehensive set of theoretical radial distributions.

Instabilities and Anomalous Diffusion in the Reflex Discharge

K. I. Thomassen

J. Appl. Phys. 39, 5017 (1968); http://dx.doi.org/10.1063/1.1655917 (8 pages) | Cited 9 times

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The instabilities of a cold‐cathode reflex discharge are studied and their relationship to the observed increase in radial transport above a critical magnetic field is discussed. High‐frequency beam‐plasma instabilities occurring in bursts, owing to a relaxation phenomenon, and low‐frequency resistive drift waves are both found, with the latter appearing to have an important role in transport.

Properties of GaP Green‐Light‐Emitting Diodes Grown by Liquid‐Phase Epitaxy

K. K. Shih and G. D. Pettit

J. Appl. Phys. 39, 5025 (1968); http://dx.doi.org/10.1063/1.1655918 (5 pages) | Cited 7 times

Online Publication Date: 19 November 2003

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Efficient and reproducible green‐light‐emitting diodes have been made by a vertical liquid‐phase epitaxial method. External quantum efficiencies of uncoated diodes as high as 3×10−4 at 300°K were obtained. The I‐V characteristics of these diodes show an exponential behavior of the form I = I0 exp eV∕βKT; values of β were generally about 2 at 300° and 77°K. The emission intensity varies with I2 at low currents, and changes to an approximately linear dependence at high currents. Emission spectra have been studied as a function of current and temperature from 27° to 670°K. Seven emission lines in the green region of the spectrum have been observed, and the origins of these radiative recombinations have been studied. At low temperatures, four lines are identified as pair emission. One line at intermediate temperatures is believed to be due to free‐hole‐to‐donor emission, and two lines at high temperatures may be attributed to free‐exciton recombination.

A Statistical Analysis of the Initial Microwave Tensor Susceptibility of a Polycrystalline Ferrite

Thomas A. Kriz and T. Koryu Ishii

J. Appl. Phys. 39, 5029 (1968); http://dx.doi.org/10.1063/1.1655919 (4 pages) | Cited 1 time

Online Publication Date: 19 November 2003

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The microwave tensor susceptibility of an inhomogeneous ferrite medium at remanence is analyzed statistically. A multivariate Gaussian distribution is used to characterize the magnetization of the medium as a random vector quantity. The orientation of a random vector quantity for magnetic field intensity in the medium is taken to be the same as for magnetization, but its magnitude is described with a uniform distribution. The statistical parameters of these distributions are defined as functions of such material properties as (1) the ratio of magnetization at remanence to that at saturation, (2) shape demagnetization, and (3) rf demagnetization. Numerical values of average tensor component susceptibility for several different inhomogeneous media are calculated using an analytical solution of the statistical model and shown to be within 11% of experimental results reported by other investigators.

A Preliminary Investigation of Brillouin Scattering in a Liquid Crystal

W. A. Nordland

J. Appl. Phys. 39, 5033 (1968); http://dx.doi.org/10.1063/1.1655920 (4 pages) | Cited 7 times

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Brillouin spectra have been observed in the liquid‐crystal cholesteryl‐2‐(2‐ethoxyethoxy) ethyl carbonate. The frequency shift and the relative intensities of the shifted and unshifted components have been measured as a function of temperature, which was varied through the cholesteric to isotropic transition.

Anomalous Diffusion of 14C in TiC0.67

S. Sarian

J. Appl. Phys. 39, 5036 (1968); http://dx.doi.org/10.1063/1.1655921 (6 pages) | Cited 27 times

Online Publication Date: 19 November 2003

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The self-diffusion of 14C in TiC0.67 was studied in the temperature range 1745°–2720°C. The diffusivity, which exhibits a discontinuity at 2080°C, can be represented by two expressions: D*0.67 = (2.85±0.20)×10−4exp[−(49 600±300)/RT] cm2/sec above 2080°C and D*0.67 = (1.14±0.66)×102exp[−(109,900±2000)/RT] cm2/sec below this temperature. No discontinuity was found in carbon saturated TiC0.97 and the self-diffusion coefficient for this composition can be described to a temperature of 2720°C by the single expression D*0.97=(6.98±1.24) exp[−(95 300±700) / RT] cm2/sec.

The Diffusion of Copper in Iron

S. J. Rothman, N. L. Peterson, C. M. Walter, and L. J. Nowicki

J. Appl. Phys. 39, 5041 (1968); http://dx.doi.org/10.1063/1.1655922 (4 pages) | Cited 20 times

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Measurements of the diffusion of 64Cu in pure and impure α and γ iron show a large discontinuity in the Arrhenius plot of the lattice diffusion coefficient at the α‐γ transformation, contrary to the data of Anand and Agarwala [J. Appl. Phys. 37, 4248 (1965)]. Grain‐boundary diffusion predominates at T≤815°C in the α phase and at T≤1250°C in the γ phase. Trapping of the radioactive copper by inclusions or impurities in solution also appears to have a profound effect on the diffusion process.

Rotation and Translation of Islands in the Growth of Heteroepitaxial Films

H. Reiss

J. Appl. Phys. 39, 5045 (1968); http://dx.doi.org/10.1063/1.1655923 (17 pages) | Cited 63 times

Online Publication Date: 19 November 2003

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A simple yet realistic model is introduced for the description of islands of epitaxial overgrowth on a substrate surface. The model is employed to examine the potential energy surface for both rotation and translation of the islands as a whole. It is shown that one or more overwhelmingly easy directions of orientation exist, and that islands which manage to be rotated out of these easy directions can both rotate and translate with activation energies of the order of magnitude of the activation energy for surface diffusion of isolated atoms. The results provide semiquantitative support for Bassett's observation via the electron microscope that large islands of overgrowth (∼1000 atoms) seem to both rotate and translate. Considerations of surface nucleation indicate that although nucleation rate depends on orientation, subsequent growth of islands does not. A growth law independent of orientation is then derived. It is also shown semiquantitatively that under typical experimental conditions for slow deposition, nucleation occurs but once—islands initially formed grow, while their number remains constant. This result is also consistent with several observations. The process by means of which misoriented islands anneal by rotational diffusion into the easy orientation, while they simultaneously grow, is analyzed. A formula is developed which indicates that under certain conditions, islands of overgrowth become ``stuck'' in misoriented positions before they coalesce. The conditions effecting this phenomenon are discussed. General comments and observations are made concerning the initial origin of misoriented nuclei, and means are suggested for adjusting conditions so as to permit misorientation to anneal before coalescence. Typical densities of dislocations introduced by misorientation are estimated. Crucial experiments are suggested for examining the hypothesis of this paper.

Magnetic and Magneto‐optic Properties of EuO Films Doped with Trivalent Rare‐Earth Oxide

K. Y. Ahn and T. R. McGuire

J. Appl. Phys. 39, 5061 (1968); http://dx.doi.org/10.1063/1.1655924 (5 pages) | Cited 23 times

Online Publication Date: 19 November 2003

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The ferromagnetic Curie temperature of EuO films has been increased by selective doping with trivalent rare‐earth oxides. The electrical resistivity, which depends upon the temperature and has a broad peak at ≈100°K, decreases markedly to ≈10−1 Ω⋅cm with doping. A typical ferromagnetic Curie temperature, determined from magneto‐optic measurements in zero applied field, is ∼135°K. Maximum longitudinal Faraday rotation occurs at 0.65 μ with a specific rotation of +1×105 deg∕cm for an incidence angle of 20 deg. At 0.84 μ the Faraday rotation reverses sign and reaches a negative maximum at 0.93 μ. The longitudinal Kerr rotation also has two maxima at 0.58 μ and 0.83 μ with double rotations of ≈4°. The transverse Kerr effect depends on the wavelength in the same manner and has maximum values of +0.4 and −0.3, respectively. There is a strong optical absorption band centered at 0.6 μ (at 300°K) with α≈1.2×105 cm−1 which shifts toward longer wavelengths at lower temperatures accompanied by a small decrease in α. An additional absorption band centered around 0.4 μ with amplitude less than 10% of the main absorption peak appears as a result of doping. Quasistatic switching measurements show that the coercive force depends strongly upon the stress in films arising from the difference in thermal expansion coefficients of EuO and substrates. Hc is typically 120 and 60 Oe on fused quartz and 0080 glass, respectively, with remanence of ∼0.7. Results of the transport, magnetic, magneto‐optical, and optical properties are discussed in terms of indirect exchange via conduction electrons.

Dominant Surface Electronic Properties of SiO2‐Passivated Ge Surfaces as a Function of Various Annealing Treatments

T. O. Sedgwick

J. Appl. Phys. 39, 5066 (1968); http://dx.doi.org/10.1063/1.1655925 (12 pages) | Cited 12 times

Online Publication Date: 19 November 2003

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The metal‐oxide‐semiconductor (MOS), capacitance vs applied voltage (C‐V) measurement technique was used to investigate SiO2‐passivated Ge surfaces as a function of high‐temperature annealing treatments in H2, O2, N2, and H2O. Capacitance measurements were made at high frequencies (100 MHz) and∕or reduced temperatures (145°, 77°K) to eliminate the capacitive contribution of fast surface states to the ac signal. Since the surface states did equilibrate with the superimposed applied dc voltage, is was possible to determine surface‐state type, energy, and densityfrom voltage shifts in the C‐V traces. Hydrogen annealing at 600°C or above introduces a high density (>1013∕cm2) of fast acceptor states. These states are located at the center of the Ge energy gap. In addition, hydrogen annealing at 700°–800°C introduces acceptors close to the valence band or fixed negative charge. Most of these hydrogen‐induced states are removed by annealing in oxygen or water vapor at 230°–440°C. At the same time the oxygen or water vapor exposure introduces an effective positive charge density of 1–5×1012∕cm2. This positive charge is due either to donors lying close to the conduction band edge or to fixed positive charge. The above effects are reversible.

Dielectric Breakdown and Recovery of X‐Cut Quartz under Shock‐Wave Compression

R. A. Graham and W. J. Halpin

J. Appl. Phys. 39, 5077 (1968); http://dx.doi.org/10.1063/1.1655926 (6 pages) | Cited 24 times

Online Publication Date: 19 November 2003

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While a shock wave is traversing a disk of X‐cut quartz, a piezoelectric current flows in an external circuit connected across the faces of the disk. In this paper measurements of this current are used to study dielectric breakdown and subsequent recovery which occurs in quartz. Quartz specimen disks were impacted at various stress levels in such a way as to produce shock waves that propagated along the X axis either in the direction of or opposite to that of the pressure‐induced polarization. In the latter case, short‐circuit current measurements show that breakdown occurs at a threshold stress greater than 10 and less than 13 kbar. Since the impact experiment produced one‐dimensional electrical and mechanical conditions in the specimen disk, it was possible to formulate a mathematical model that permitted solutions for internal electrical fields and resistivity in terms of the measured current. Computations with this model show that the field in the stressed portion of the disk at breakdown is about 7.0×105 V∕cm, which is an order of magnitude lower than the value observed at atmospheric pressure. Computations with the model also show that recovery from breakdown to essentially infinite values of resistivity occurs during the transit time of the shock wave when the field in the stressed region of the disk is ``quenched'' to a value of about 1.9×105 V∕cm. This critical field appears to be the same for all shock stress levels investigated from 13 to 35 kbar. The dependence of the initiation of breakdown on the direction of wave propagation relative to the polarization direction indicates that the shock‐wave front furnishes a source of free electrons.

Room‐Temperature Faraday Rotation in n‐Type InSb Films at 23.4 GHz

D. J. White

J. Appl. Phys. 39, 5083 (1968); http://dx.doi.org/10.1063/1.1655927 (4 pages) | Cited 2 times

Online Publication Date: 19 November 2003

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Measurements were made of Faraday rotation on ∼1 μ thick evaporated and recrystallized polycrystalline InSb films. The experiments were carried out at room temperature using TE11 circular waveguide with dc magnetic fields up to 7 kOe. Rotations on the order of 50 deg were observed. The experimental results are in reasonable agreement with a theoretical model based on free‐carrier Faraday rotation, including multiple reflections, using the mobilities and carrier concentrations found by separate dc measurements.

Photosensitivity in Epitaxial PbS Films

H. R. Riedl and R. B. Schoolar

J. Appl. Phys. 39, 5086 (1968); http://dx.doi.org/10.1063/1.1655928 (7 pages) | Cited 7 times

Online Publication Date: 19 November 2003

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A study has been made of the photosensitivity in epitaxial PbS films which were sensitized by heat treatments in air or sulfur vapor. The sensitizing process results in the formation of narrow lines of material which are more p type than the host film. The resultant junctions are responsible for the photosensitivity. The junctions are associated with crystal defects which are faintly visible under a microscope and appear as lines running in (100) directions. Introduction of these lines can be sufficiently controlled so that only a few are introduced into a sample. This enables individual junctions to be studied. Various properties of the epitaxial films were determined and compared to the corresponding properties of the well‐known polycrystalline PbS detectors.

Optical Probing of Inhomogeneities in n‐GaAs with Applications to the Acoustoelectric Instabilities

David L. Spears and Ralph Bray

J. Appl. Phys. 39, 5093 (1968); http://dx.doi.org/10.1063/1.1655929 (9 pages) | Cited 11 times

Online Publication Date: 19 November 2003

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A study is presented of the intimate relationship between current instabilities of acoustoelectric origin in n‐GaAs at 77°K and the inhomogeneity in the Ohmic resistivity of the samples. In order to correlate various aspects of the acoustoelectric instabilities with the sample inhomogeneities, two optical probing techniques were developed for determining the Ohmic‐resistivity profile with good spatial resolution, ⪝0.1 mm. One involves the measurement of the local photoconductance in the sample, which is related to the local dark resistivity; the other method involves the measurement of the change in optical transmission produced by the local thermal shift in the intrinsic absorption edge when the sample is heated by a high current pulse. The change in optical transmission is related to the local resistivity. The acoustic flux distribution in the sample is determined by yet another optical probe, utilizing the modulation in transmission produced by the high acoustic‐energy density in the domain. Several aspects of the acoustoelectric effects are themselves useful for gauging the homogeneity of the samples. In particular, the propagating acoustoelectric domain serves as a convenient probe of the carrier concentration. These techniques are applied to the analysis of the form of the current instabilities, the distribution of the acoustic flux in the sample, and the domain‐formation process. The presence of a somewhat higher resistance, hence higher acoustoelectricgain region, at the upstream end near the cathode is shown to contribute to the formation of propagating acoustoelectric domains.

Growth of Two‐ and Three‐Dimensional Space Charge from Negative Differential Resistivity

John A. Copeland

J. Appl. Phys. 39, 5101 (1968); http://dx.doi.org/10.1063/1.1655930 (3 pages) | Cited 2 times

Online Publication Date: 19 November 2003

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Some simple cases are considered of two‐ and three‐dimensional space‐charge growth in a semiconductor such as GaAs which can exhibit a negative differential resistance to the one component of small perturbation electric fields parallel to a large bias electric field. These indicate that finite space‐charge distributions will generally grow much slower than previous one‐dimensional calculations have suggested for infinite layer distributions. This is because the differential resistance is always positive to components of the perturbation field perpendicular to the bias field.

Hot‐Electron Transport in Al☒Al2O3 Triodes Produced by Plasma Oxidation

E. E. Huber, F. L. Johnston, and C. T. Kirk

J. Appl. Phys. 39, 5104 (1968); http://dx.doi.org/10.1063/1.1655931 (13 pages) | Cited 6 times

Online Publication Date: 19 November 2003

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The measurement of tunnel triodes by a small ac signal r parameter technique is shown to give a new way of directly measuring the oxide barrier height and barrier asymmetry. This type of measurement permits distinguishing between true hot‐electron collection and leakage currents. A saturation of the hot electron transport coefficient has been found vs the emitter‐base bias. The most direct explanation for this saturation is that those hot electrons which are collected are mainly ballistic, i.e., that they have come from the emitter with little or no momentum change due to collisions. The Al base attenuation length has been measured to be 150 Å at 77°K for electrons 2.0 eV above the Fermi level. Collector‐voltage dependence of the triode has been explained on the basis of electron‐phonon losses in the collector oxide. The major part of the large hot electron attenuation factor in these triodes cannot be explained by either metal base losses or electron‐phonon losses in the oxides, which together give rise to an attenuation factor of ≈ (¼) in a typical triode. An interfacial loss mechanism appears to be the most likely explanation for the large attenuation factor of ≈ (1∕100) remaining after taking the above volume losses into account.

A Simplified Orders‐of‐Scattering Technique for Calculating the Absorption of X Rays

Robert G. Willis

J. Appl. Phys. 39, 5116 (1968); http://dx.doi.org/10.1063/1.1655932 (6 pages)

Online Publication Date: 19 November 2003

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A simple, efficient technique is described for calculating the energy absorption in a planar slab of finite thickness from a planar source of x rays. Compton scattering and photoelectric absorption are considered as the attenuation processes. The computational model allows two scattering angles per Compton event, and in this form is amenable to closed‐form solution. Results are given for several absorbers in the energy range from 25 to 400 keV, and comparisons are made with Monte Carlo calculations. Good agreement is obtained at depths of at least three mean free paths. In all cases, the Monte Carlo calculation required at least 100 times the computation time of the simplified orders‐of‐scattering technique.

Direct Basal‐Plane Shear in Single‐Crystal Graphite

D. E. Soule and C. W. Nezbeda

J. Appl. Phys. 39, 5122 (1968); http://dx.doi.org/10.1063/1.1655933 (18 pages) | Cited 37 times

Online Publication Date: 19 November 2003

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The basal‐plane shear stress‐strain behavior of small, highly anisotropic‐annealed natural graphite single crystals was studied at room temperature. A static uniaxial‐shear stress was applied directly along the basal plane with a minimum of normal force, incorporating a technique to detect translations down to ∼40 Å. Comparative measurements were also made on compression‐annealed pyrolytic graphite. The staticshear modulus G was also corroborated by a modified ultrasonic transit‐time method. Basal‐plane dislocation systems strongly reduce the measured G, where values of (0.013–0.14)×1011 dyn∕cm2 were observed. This reduction is found to be caused primarily by a dislocation concentration of ∼2×106 cm−2. The average critical‐resolved shear stress σc was 0.29×106 dyn∕cm2, and an analysis of the relation between σc and the critical breakaway stress for dislocation pinning shows that dislocation line segments l≃120–310 μ are operative. Plastic curvature of the stress‐strain curves shows the effect of very sensitive creep and glissile slip. Laminar flow in this principal slip direction produces a plastic strain ϵ* = Aσ4.2 analogous to easy glide in hcp metals along the close‐packed direction. Classical Andrade t1∕3 creep was observed at higher stresses and approached a logarithmic creep behavior with decreasing stress. A saturation effect seen in the shear‐strength σs with shear‐fracture cycling leads to a resultant σs of (2.5–7.5)×106 dyn∕cm2. Possible contributions to the elastic shear strain, including dislocations, grain boundaries, hard inclusions, delamination voids, and the Fermi‐level shift, are considered as they affect the measured shear modulus. Dislocation pinning by boron ions, in the dilute concentration range from 7 ppm B up to 1500 ppm B, was found to produce a large increase in G with eventual saturation. After accounting for all known shear‐strain components, this saturation value leads to an intrinsic single‐crystal graphite C44 value of (0.45±0.06)×1011 dyn∕cm2.

Observations Concerning Radiative Efficiency and Deep‐Level Luminescence in n‐Type GaAs Prepared by Liquid‐Phase Epitaxy

H. Kressel, F. Z. Hawrylo, M. S. Abrahams, and C. J. Buiocchi

J. Appl. Phys. 39, 5139 (1968); http://dx.doi.org/10.1063/1.1655934 (6 pages) | Cited 31 times

Online Publication Date: 19 November 2003

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A study was made of n‐type GaAs prepared by liquid‐phase epitaxy doped with Si, Ge, Sn, Te, and Se by photoluminescence and Te‐doped material by transmission‐electron microscopy. A broad emission band centered at 1.2 eV (band B) is observed in LPE materials doped with group VI elements. Band B increases in intensity relative to the bandgap radiation with increasing dopant concentration in the 1018 cm−3 range. It is suggested that the recombination centers responsible for band B are the neutral (VGa+3 Te) complexes postulated by Vieland and Kudman, and that these represent the solid solution of Ga2Te3 in GaAs. With increasing dopant content, the solubility limit is eventually exceeded, and precipitates of this compound are then formed. These have been observed and identified by transmission‐electron microscopy. The radiative efficiency falls off sharply with increasing dopant content beyond 2–3×1018 cm−3 in materials doped with Se and Te. It is suggested that this fall off is partly due to nonradiative recombination via small precipitates, each containing on the order of 1000 dopant atoms.

Plastic Deformation of α‐Arsenic Single Crystals

M. N. Shetty and J. B. Taylor

J. Appl. Phys. 39, 5145 (1968); http://dx.doi.org/10.1063/1.1655935 (5 pages) | Cited 3 times

Online Publication Date: 19 November 2003

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Plastic deformation and fracture of α‐arsenic (rhombohedral) single crystals tested in tension with fixed and random orientations is analyzed using current dislocation concepts. With〈1math0〉 as the most probable slip vector, elastic moduli are determined for the observed slip systems, and surface free energies for the fracture surfaces are estimated from the elastic moduli.

A Technique for Trap Determinations in Low‐Resistivity Semiconductors

L. R. Weisberg and H. Schade

J. Appl. Phys. 39, 5149 (1968); http://dx.doi.org/10.1063/1.1655936 (3 pages) | Cited 22 times

Online Publication Date: 19 November 2003

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A simple method is described to allow the use of thermally stimulated conductivity (TSC) measurements for low‐resistivity semiconductors. A p‐n junction or Schottky barrier is formed to provide the required high‐resistivity region. Trap populations can be inverted either by light or by changes in diode bias, but different traps may be seen in each case. The accuracy of trap concentration determinations is improved over ordinary TSC measurements since the gain is close to unity, and the active volume can be accurately found from capacitance measurements. The use of the method is demonstrated by the measurement of trap energies and densities in a sample of GaAs0.5P0.5 alloy with an electron concentration of about 1015 cm−3. Two main traps were seen, one at 0.20 eV from the conduction band and the other at 0.41 eV from the valence band, with concentrations of, respectively, 1×1014 cm−3 and 5×1014 cm−3. The method has also been successfully applied to silicon.

Crystal Structure of Vapor‐Deposited Boron Filaments

P. F. Lindquist, M. L. Hammond, and R. H. Bragg

J. Appl. Phys. 39, 5152 (1968); http://dx.doi.org/10.1063/1.1655937 (11 pages) | Cited 5 times

Online Publication Date: 19 November 2003

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The structure of boron filaments, vapor‐deposited on a tungsten‐wire substrate in the temperature range 870°–1260°C, is studied by x‐ray diffraction and transmission‐electron microscopy. The typical diffraction pattern observed with both x rays and electrons consists of six or seven broad maxima, or halos. This pattern is interpreted as arising from a microcrystalline (∼30 Å diam) material having an average unit‐cell structure intermediate between the α‐rhombohedral and ``simple'' tetragonal polymorphs of boron. This interpretation appears to be more satisfactory than others based on an ``amorphous'' or ``faulted fcc'' description, although several discrepancies remain to be explained. Single‐crystal spot patterns are also observed in the electron microscope. These arise from inclusions of α‐ and β‐rhombohedral boron, less than 1 μ in diameter, which are distributed throughout the microcrystalline matrix. These inclusions constitute a very small volume fraction of the vapor‐deposited boron and are not detected by x‐ray diffraction.
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