Showing papers in "Journal of Applied Physics in 1977"

The work function of the elements and its periodicity

Abstract: A new compilation, based on a literature search for the period 1969–1976, is made of experimental data on the work function. For these 44 elements, preferred values are selected on the basis of valid experimental conditions. Older values, which are widely accepted, are given for 19 other elements on which there is no recent literature, and are so identified. In the data for the 63 elements, trends that occur simultaneously in both the columns and the rows of the periodic table are shown to be useful in predicting correct values and also for identifying questionable data. Several illustrative examples are given, including verifications of predictions published in 1950.

Photoelectrolysis and physical properties of the semiconducting electrode WO2

Abstract: The behavior of semiconducting electrodes for photoelectrolysis of water is examined in terms of the physical properties of the semiconductor. The semiconductor‐electrolyte junction is treated as a simple Schottky barrier, and the photocurrent is described using this model. The approach is appropriate since large‐band‐gap semiconductors have an intrinsic oxygen overpotential which removes the electrode reaction kinetics as the rate‐limiting step. The model is successful in describing the wavelength and potential dependence of the photocurrent in WO3 and allows a determination of the band gap, optical absorption depth, minority‐carrier diffusion length, flat‐band potential, and the nature of the fundamental optical transition (direct or indirect). It is shown for WO3 that minority‐carrier diffusion plays a limited role in determining the photoresponse of the semiconductor‐electrolyte junction. There are indications that the diffusion length in this low carrier mobility material is determined by diffusion‐controlled bulk recombination processes rather than the more common trap‐limited recombination. It is also shown that the fundamental optical transition is indirect and that the band‐gap energy depends relatively strongly on applied potential and electrolyte. This effect seems to be the result of field‐induced crystallographic distortions in antiferroelectric WO3.

X-ray photoemission spectroscopy studies of Sn-doped indium-oxide films

Abstract: The In and Sn 3d3/2 and 3d5/2 ESCA peaks and the oxygen 1s peak of Sn‐doped In2O3 films were compared with those for In2O3 films and In2O3, SnO, SnO2, and Sn3O4 powders. Comparison of as‐grown with sanded surfaces revealed Sn‐rich surface layers in.those films having good optical and transport properties. These experimental fins are interpreted with a schematic energy‐band model and the assumption that film darkening in Sn‐doped In2O3 films is caused by the formation and growth of an Sn3O4‐like second phase in the bulk. Suppression of these phase could be accomplished by higher substrate temperatures, which permit equilibrium conditions to be attained. Sn‐rich phases to migrate to the films surface, and the tine disproportionates to Sn2+ and Sn4+ ions.

Negative bias stress of MOS devices at high electric fields and degradation of MNOS devices

Abstract: One of the most important degradation effects observed in MNOS memory transistors is a negative shift of the threshold window. This negative shift is caused by a strong increase of the density of Si‐SiO2 surface traps. This effect has been proposed to be caused by the same effect that is observed in MOS devices subjected to negative‐bias stress (NBS). In this paper, a detailed study of the increase of the number of surface traps in MOS structures after NBS at temperatures (25–125 °C) and fields (400–700 MV/m) comparable to those used in MNOS devices is presented. Two different behaviors are observed. At low fields the surface‐trap density increases as t1/4 and at high fields it increases linearly with the stress time t. The low‐field behavior is temperature and field dependent and the zero‐field activation energy is determined to be 0.3 eV. The high‐field behavior is strongly field dependent but independent of temperature. A physical model is proposed to explain the surface‐trap growth as being diffusion ...

Temperature rise induced by a laser beam

Abstract: The spatial distribution of the temperature rise induced by a laser beam absorbed in a solid is reduced to a one‐dimensional integral which is evaluated numerically. The solution for a general laser intensity distribution is specialized to the case of a Gaussian beam. A closed‐form expression in terms of tabulated functions is obtained for the maximum temperature rise.

Heat treating and melting material with a scanning laser or electron beam

Abstract: A thermal analysis for laser heating and melting materials is derived for a Gaussian source moving at a constant velocity. The resulting temperature distribution, cooling rate distribution, and depth of melting are related to the laser spot size, velocity, and power level. As the power is increased to heat the liquid above the boiling point, a transition to deep penetration welding is described. Calculations are presented for 304‐stainless steel which are in agreement with experiment.

Reordering of amorphous layers of Si implanted with 31P, 75As, and 11B ions

Abstract: The effect of impurities on the epitaxial regrowth of Si from amorphous layers created by ion implantation into 〈100〉 and 〈111〉 Si was studied by channeling effect measurements with 2‐MeV 4He ions. The Si wafers were first implanted at −180 °C with 28Si ions to form amorphous layers approximately 4000 A thick and then were implanted with 31P, 75As, or 11B ions to concentration levels of about 0.2–0.5 at.%. For these layers with impurity species the growth rate is found to be significantly higher than for those without. The measured regrowth rate at 500 °C for 〈100〉 Si with an impurity concentration of ∼2×1020 cm−3 of 31P or 75As is a factor of 6 greater, and of 11B a factor of 20 greater, than the regrowth rate in amorphous layers without impurities. For the case of 31P implanted 〈100〉 Si the activation energy of regrowth is close to that (2.35 eV) found for impurity‐free amorphous layers and for 11B implanted samples the energy is 1.9 eV. For 〈111〉 31P implanted Si specimens there is an increase in growth rate over that found in impurity‐free samples and a high level of residual disorder.

Surface rippling induced by surface‐tension gradients during laser surface melting and alloying

Abstract: During laser surface melting and alloying, temperature gradients on the melt surface between the laser‐beam impact point and the intersection line of the solid‐liquid interface with the surface generate surface‐tension gradients that sweep liquid away from beam impact point. The resulting flow of liquid creates a depression of the liquid surface beneath the beam and ridging of the liquid surface elsewhere. As the beam passes to other areas of the surface, this distortion of the liquid surface is frozen in, creating a roughened rippled surface. If the laser‐beam sweep velocity exceeds a critical velocity, the liquid does not have sufficient time to form ripples, and rippling from surface‐tension gradients can be avoided.

Enhanced elastic modulus in composition‐modulated gold‐nickel and copper‐palladium foils

Abstract: The biaxial elastic modulus Y[111] has been measured by bulge testing in Au‐Ni and Cu‐Pd foils containing short‐wavelength one‐dimensional composition modulations produced by vapor deposition. As compared with homogeneous foils of the same average composition, the modulated foils exhibited an appreciable increase in modulus—from 0.21 to 0.46 TPa for Au‐Ni and from 0.27 to 1.31 TPa for Cu‐Pd. For the latter system, the increase was found to be proportional to the square of the amplitude of the modulation. The enhancement of the modulus decreased with increasing wavelength and for wavelengths greater than 3 nm the modulus was the same as that for homogeneous foils. It was also observed that the deformation was non‐Hookian; the slope of the stress‐strain curves decreased with increasing strain.

Aggregation and migration of ion‐implanted silver in lithia‐alumina‐silica glass

Abstract: The near‐surface nucleation and crystallization behavior of Ag+ ion‐implanted lithia‐alumina‐silica glasses has been studied. For room‐temperature Ag implants, crystallization of the glass ceramic phase was prevented by dissolution of Ag precipitates and migration of Ag atoms at temperatures below that necessary for formation of the glass ceramic phase. Crystallization was demonstrated after low‐temperature or low‐dose‐rate implantations. Optical spectroscopy was used to monitor the size of colloidal Ag particles and to detect the presence of the crystalline phase. Rutherford backscattering spectroscopy (RBS) was used to obtain the depth distribution of Ag atoms in the glass and thus monitor Ag migration. For samples implanted at room temperature and at relatively high dose rates (∼1 μA/cm2), aggregation of the Ag atoms into colloids occurred during implantation and also during subsequent annealing to temperatures ?350 °C. The RBS spectra indicate some migration of the Ag to the surface at these temperatu...

Accurate determination of liquid‐crystal tilt bias angles

Abstract: A detailed analysis is given for three techniques used to determine the tilt bias angle of a nematic liquid crystal in contact with a boundary surface. Two of these methods, the crystal rotation and capacitive methods, have severe disadvantages, such as a restricted range of application, an insufficient accuracy, and sometimes require knowledge of nematic material constants which have to be determined by separate experiments. A third and more useful method, a magnetic null method, makes it possible to determine the tilt bias angle directly with only one measurement to an accuracy of 0.1°, regardless of the size of the angle or the nature of the nematic liquid crystal. Using the magnetic null method we have investigated the tilt bias angles of nematics in contact with glass substrates onto which a coating of SiO had been obliquely evaporated. We find that the tilt bias angle decreases with increasing evaporation angle (both angles measured from sample plane) until a critical evaporation angle of ?14° is reached, whereupon the director reorients out of the plane of incidence of the evaporation beam and assumes a direction normal to this plane with a 0° tilt bias. We also find that the tilt bias angle varies from compound to compound for the same evaporation parameters and is influenced by temperature and trace impurities.

Influence of 16O, 12C, 14N, and noble gases on the crystallization of amorphous Si layers

Abstract: Channeling effect measurements have been used to study the effect of impurities on the epitaxial regrowth of amorphous silicon layers on single‐crystal silicon. Implantation was used to form the amorphous layers and also to introduce the impurities 12C, 14N, 16O, 20Ne, 40A, and 84Kr. For 16O implants, the growth rate at 550 °C depended on the 16O concentration and at the level of 0.5 at.% the rate was reduced from about 90 to about 10 A/min. For similar atomic concentrations of 14N, the rate was comparable to the 16O case. For comparable concentrations of 12C, the regrowth rate was found to be three times higher than for that of the 16O case. Noble gas ions are also found to retard the growth rate of the amorphous layers. For 40Ar at about the 0.5‐at.% level, the regrowth rate is appreciably slower than even that for the 16O case.

Linear thermal expansion measurements on silicon from 6 to 340 K

Abstract: Linear thermal expansion measurements have been carried out from 6 to 340 K on a high‐purity silicon sample using a linear absolute capacitance dilatometer. The accuracy of the measurements varies from ±0.01×10−8 K−1 at the lowest temperatures to ±0.1×10−8 K−1 or 0.1%, whichever is greater, near room temperature, and is sufficient to establish silicon as a thermal expansion standard for these temperatures. The agreement with previous data is satisfactory at low temperatures and excellent above room temperature where laser‐interferometry data of comparable accuracy exist. Thermal expansions calculated from ultrasonic and heat‐capacity data are preferred below 13 K where experimental problems occurred.

Emission probability of hot electrons from silicon into silicon dioxide

Abstract: An experimental method is described for directly measuring the probability of electron emission from the silicon substrate into the SiO2 layer after the electron has fallen through a certain potential drop in traversing the depletion layer and reached the Si‐SiO2 interface. The method is based on optically induced hot‐electron injection in polysilicon‐SiO2‐silicon field‐effect‐transistor structures of reentrant geometry. The emission probability was studied as a function of substrate doping profile, substrate voltage, gate voltage, and lattice temperature. It was found that the hot electrons could be emitted by tunneling as well as by surmounting the Schottky‐lowered barrier. Over‐the‐barrier emission dominates at large substrate voltages, where the emission probability is high, and tunnel emission becomes appreciable and may even dominate at small substrate voltages where the emission probability is low. A simple model was developed based on the assumption that only those hot electrons lucky enough to escape collision with optical phonons were emitted. Using this model, we found that the expression P=A exp(−d/λ) described very well the dependence of the emission probability on doping profile, substrate voltage, and gate voltage. Here A=2.9 is a constant, λ is the optical‐phonon‐electron collision mean free path, d is the distance from the Si‐SiO2 interface where the potential energy is equal to the ’’corrected’’ barrier of (3.1 eV−βEOX1/2 −αEOX2/3ox), βEOX1/2 is the Schottky lowering of the barrier, and αEOX2/3 is a ’’barrier‐lowering’’ term introduced to account for the probability of tunneling. The temperature dependence of the collision mean free path was found to follow the theoretical relationship λ=λo tanh(ER/2kbT), with λo=108 A and ER=0.63 eV. This model is useful for evaluating potential hot‐electron‐related instability problems in IGFET and similar structures.

Electrical properties and conduction mechanisms of Ru‐based thick‐film (cermet) resistors

Abstract: This paper presents an experimental study of the electrical conduction mechanisms in thick‐film (cermet) resistor. The resistors were made from one custom and three commercially formulated inks with sheet resistivities ranging from 102 to 106 Ω/⧠ in decade increments. Their microstructure and composition have been examined using optical and scanning electron microscopy, electron microprobe analysis, x‐ray diffraction, and various chemical analyses. This portion of our study shows that the resistors are heterogeneous mixtures of metallic metal oxide particles (∼4×10−5 cm in diameter) and a lead silicate glass. The metal oxide particles are ruthenium containing pyrochlores, and are joined to form a continuous three‐dimensional network of chain segments. The principal experimental work reported here is an extensive study of the electrical transport properties of the resistors. The temperature dependence of conductance has been measured from 1.2 to 400 K, and two features common to all resistors are found. Th...

Effects of laser-modulated particulate incandescence on Raman scattering diagnostics

Abstract: Laser‐modulated particulate (soot) incandescence has been studied by measuring the laser‐driven particle surface temperature in a propane diffusion flame as a function of laser focal flux. The experimental results display fair agreement with an analytical model of the process. Quite importantly, the absolute incandescence level displays a saturation behavior with increasing laser pulse energy. For laser Raman scattering diagnostics, this behavior means that the S/N ratio will increase with increasing laser flux level. Thus, for highest S/N ratio, it is preferable to operate at the highest possible flux short of gas breakdown and/or optical‐component damage levels.

Velocity‐field characteristics of GaAs with Γc6‐Lc6‐Xc6 conduction‐band ordering

Abstract: This paper describes Monte Carlo calculations of velocity‐field characteristics for GaAs using the recent experimental conduction‐band ordering of Aspnes, which places the Lc6(111) conduction‐band minima lower in energy than the Xc6(100) minima. These calculations use intervalley deformation potentials which give the best fit to recent high‐field drift velocity measurements, and at the same time give good agreement with accepted peak velocity and threshold field values.

Transient and steady‐state electron transport properties of GaAs and InP

Abstract: A Monte Carlo computer technique has been used to calculate nonequilibrium electron transport properties of n‐type GaAs and InP at 77 and 300 K, with and without impurity scattering. Characteristics of the electron transient, including velocity overshoot, are presented and analyzed in terms of energy and momentum relaxation times. New information about the steady‐state transport properties of InP and about the electron temperatures of GaAs and InP as functions of electric field is also presented and discussed.

Influence of particle size ratio on the continuity of aggregates

Abstract: A model is developed which considers the volume fraction of dispersed phase necessary to form an infinitely long network as a function of the particle size ratio. Recognizing that neither a monolayer nor a double layer of dispersed particles around the primary phase is a necessary condition for continuity, the surface fraction of primary phase covered by the dispersed phase and the ratio of dispersed phase particles which are occluded from, versus contiguous to, the primary phase are estimated either empirically or by reference to probability theory. The theoretical results are compared with earlier experimental work on electrical properties of compacted mixtures of polymer and metal powders.

Optical and photoconductive properties of discharge‐produced amorphous silicon

Abstract: Optical and photoconductive properties of discharge‐produced amorphous silicon (a‐Si) of the type used in efficient thin‐film solar cells have been studied as a function of a wide range of deposition conditions The optical absorption, optical band gap, photoconductivity, hydrogen content, and the characteristics of the Si‐H vibrational mode in a‐Si were determined Both substrate temperature in the range ∼200–400 °C and the type of discharge used are found to be important factors in determining the measured optical and photoconductive properties of a‐Si For films produced at substrate temperatures near 200 °C, dihydride bonding occurs, and the optical band gap is about 17 eV As the substrate temerature increases, monohydride bonding is favored, the optical band gap decreases, the optical absorption increases, and the photoconductive properties improve These properties are, in part, associated with the presence of bonded hydrogen For substrate temperatures between 300 and 400 °C, the photoconductive

Self‐absorption effects on the radiative lifetime in GaAs‐GaAlAs double heterostructures

Abstract: An analysis is presented of the effects of self‐absorption of spontaneously emitted photons on the recombination lifetime of injected carriers in the active region of GaAs‐GaAlAs double heterostructures. It is shown that at moderate injection levels (∼100 A/cm2) self‐absorption effects may lengthen appreciably the net radiative lifetime of the carriers in heterostructures with thick (?1 μ) active regions. Results of the analysis are in good agreement with data of Ettenberg and Kressel on variation of carrier lifetime with active region thickness. From the analysis it is inferred that the internal quantum efficiency of radiative recombination in the device of Ettenberg and Kressel is greater than 90%.

The physics of zinc oxide varistors

Abstract: This paper presents a physical description of the action of ZnO varistors, which are complex ceramic bodies of ZnO grains sintered in an oxide flux; their conductivity is very low at low voltage, but becomes high after a certain breakdown voltage is reached. It is found that depletion layers in the ZnO adjacent to the intergranular layers of oxide flux are the principal barrier to conduction at low voltage. These depletion layers are formed because electron traps in the intergranular layer absorb electrons from the ZnO, and the oxide flux itself is found to be more conductive than the neighboring barriers; conduction within the flux is observed at low temperatures. Electrical breakdown is associated with the completion of trap filling in thin regions of the intergranular layer. This model is supported by a wide range of physical phenomena.

Semiconducting oxide anodes in photoassisted electrolysis of water

Abstract: The electrochemical properties of semiconducting anodes of TiO2, SrTiO3, BaTiO3, Fe2O3, CdO, CdFe2O4, WO3, PbFe12O19, Pb2Ti1.5W0.5O6.5, Hg2Ta2O7, and Hg2Nb2O7 in photoassisted electrolysis of water were determined. All of these oxides formed a rectifying junction with the electrolyte and anodic photocurrents were generated only with larger‐than‐band‐gap illumination. For Fe2O3, the optical absorption spectrum was different from the photoelectrochemical spectrum due to crystal field transitions. These oxides were found to be stable over certain range of pH. In a given electrolyte, the flatband potential Vfb varied linearly with the band gap. A good correlation was obtained between Vfb and the heat of formation of the oxide per metal atom per metal‐oxygen bond, but not between Vfb and the calculated Fermi energy of the oxide. This suggests that a semiconductor‐electrolyte interface may be approximated by a semiconductor‐metal junction where the barrier height is determined by the heat of formation of the me...

Narrowband operation of a pulsed dye laser without intracavity beam expansion

Abstract: A new simple cavity design for nitrogen‐laser‐pumped dye lasers is presented. Narrowband operation is achieved with a single dispersive element and without any intracavity beam expansion. The dispersive element is a diffraction grating used near grazing incidence with an additional mirror, instead of the usual Littrow arrangement. The large angular dispersion obtained results in a linewidth of 0.08 cm−1. The typical peak power obtained is 4 kW with 50 kW in the pump beam. Calculations of linewidth based on single‐pass estimates are presented and are found to be in good agreement with experimental results.

Formal aspects of the theory of the scattering of ultrasound by flaws in elastic materials

Abstract: An integral equation is used to derive formal expressions for the scattering of a plane wave from a single homogeneous flaw embedded in an isotropic elastic medium. Expressions are found for the scattered amplitudes and differential cross sections. An optical theorem is also derived.

Beryllium doping and diffusion in molecular‐beam epitaxy of GaAs and AlxGa1−xAs

Abstract: p‐type doping levels of up to 5×1019 cm−3 in GaAs and 3×1019 cm−3 in Al0.3Ga0.7As have been obtained in molecular‐beam epitaxy (MBE) with Be doping. These doping levels are more than one order of magnitude higher than can be achieved with other acceptors excepting ionized Zn, and are obtained while maintaining surface morphologies comparable to those of undoped layers. Mobilities of the Be‐doped GaAs MBE layers are comparable to those obtained in liquid‐phase epitaxy (LPE) material. Mobilities of Be‐doped Al0.3Ga0.7As MBE layers studied in this experiment are lower than those measured in LPE crystals and do not increase with decreasing doping level which indicates a high degree of donor compensation in these samples. Room‐temperature photoluminescent efficiencies obtained from the p‐MBE GaAs and AlxGa1‐xAs layers grown under As‐stabilized surface conditions also are significantly lower than those of comparably doped LPE material. This lower efficiency may be related to impurity contamination specific to the dopant source and is not observed during n‐type (Sn‐doped) GaAs layer growth under otherwise identical conditions. p (Be) ‐n (Ge) junctions have been evaluated and the results indicate that Be should be a suitable dopant for device fabrication. Doping profile measurements by the differential capacitance technique show that very abrupt (half‐width ?350 A) Be doping pulses can be realized. By observing the out diffusion of Be from these doping pulses during annealing of the diodes a value of D?1×10−15 cm2/sec for the diffusion coefficient of Be at 800° was established. It is concluded that, with the possible exception of ionized Zn, Be should emerge as the preferred acceptor in MBE growth of III–V compounds.

Absolute linear thermal‐expansion measurements on copper and aluminum from 5 to 320 K

Abstract: A linear absolute dilatometer based on a three‐terminal parallel‐plate capacitor design has been used to obtain thermal expansion data for high‐purity copper and aluminum from 5 to 320 K. These data have an absolute accuracy of ±0.1% above 20 K for copper and above 30 K for aluminum, and agree well with published data at the higher temperatures. The disagreement which exists with other data below 5 K for copper and below 15 K for aluminum is believed to be sample dependent, but the mechanism is not known. The aluminum results in this region depend on the state of annealing of the sample.

A short‐period helical wiggler as an improved source of synchrotron radiation

Abstract: A new kind of wiggler is proposed as an improved source of synchrotron radiation from high‐energy electron storage rings. The electrons are made to travel in a short‐period helix by a transverse helical magnetic field. The radiation spectrum produced is calculated and it is shown that the helical wiggler design could produce a total intensity (photons sec−1 per unit bandwidth) improvement of several hundred and a brightness (photons sec−1 per solid angle per unit bandwidth) improvement of 4×104 over the present state of the art in synchrotron radiation sources.

A model for the current‐voltage curve of photoexcited semiconductor electrodes

Abstract: A model to describe the behavior of photoexcited electrodes in an electrochemical cell is developed. In addition to the bulk semiconductor properties, the important parameters are a surface recombination parameter Sr and a surface electron transfer parameter St. It is the electron transfer process across the interface that leads to current in the external circuit. Using experimental curves for oxygen evolution at an n‐type TiO2 electrode and Hall‐Shockley‐Read recombination to determine Sr, it is shown that the I‐V curve in anodic bias is controlled by the competition between Sr and St. The physical basis for St is discussed and experimental approaches to investigate surface reactions are suggested.

A mathematical model for calculating electrical conditions in wire‐duct electrostatic precipitation devices

Abstract: A new method is developed which can be used to calculate electrical conditions in wire‐duct electrostatic precipitation devices. The method, based upon a numerical solution to the governing differential equations under a suitable choice of boundary conditions, accounts for the effect of space charge and is applicable over the entire range of current and voltage before sparkover. The procedure yields voltage‐current characteristics and determines the electric potential and electric field strength as functions of position for each current and applied voltage. Predictions of the theory are compared with existing experimental data and the agreement is excellent.