By Topic

Journal of Applied Physics

Issue 1 • Date Jul 1996

Filter Results

Displaying Results 1 - 25 of 100
  • Issue Table of Contents

    Page(s): toc1
    Save to Project icon | PDF file iconPDF (86 KB)  
    Freely Available from IEEE
  • Determination of the spatial distribution of a physical parameter from the distribution of another physical variable— a differential inverse problem

    Page(s): 1 - 7
    Save to Project icon | PDF file iconPDF (283 KB)  

    We propose a new type of inverse problem, in which the spatial distribution of the relative value of a physical parameter can be determined only from the distribution of another physical variable in the region of interest if there is no source in that region. The inverse problem proposed here has two features different from conventional remote probing type problems. One is that the physical variable data are given throughout the region of interest although the number of data variables is insufficient to determine directly the physical parameter of interest, while only remote data are given in a conventional problem. The other is the mathematical structure of the inverse problem: this new inverse problem yields a spatial differential equation on the target parameter, while the conventional problem becomes an integral equation on the target parameter. To show the nature of the problem, we formulated an illustrative inverse problem on the steady‐state electric current field, in which the spatial distribution of the relative conductivity can be determined from the distribution of either the potential or the current density. We give examples of computational results obtained when using the simulated potential data and the current density data. This proposed formalism for a new type of inverse problem could provide a new approach and open up new measurement schemes in many fields of science and engineering. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optical collimation and compression of a thermal atomic beam

    Page(s): 8 - 14
    Save to Project icon | PDF file iconPDF (203 KB)  

    We have performed an experiment to optically cool and compress a thermal beam of sodium atoms by employing a two‐dimensional version of a magneto‐optical trap. The beam compressor employs a tapered transverse magnetic field gradient formed by four pairs of permanent magnets. We measure the efficiency of collimation and compression as function of longitudinal velocity group. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Backscattering of an electromagnetic missile by a metal cylinder of degree higher than two

    Page(s): 15 - 24
    Save to Project icon | PDF file iconPDF (223 KB)  

    The backscattering of an electromagnetic missile from a perfectly conducting curved obstacle is investigated. The obstacle is assumed to have zero curvature just at the point of reflection of the incident pulse. The asymptotic dependence of the backscattered energy is sought, as the distance separating the obstacle from the source of the incident pulse tends to infinity. The backscattered energy is found to depend on the rate at which the energy spectral density of the current pulse at the source decays with increasing frequency, as well as on the degree of flatness of the obstacle at the point of reflection. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optical response in two‐dimensional optical superlattices with Kerr nonlinearity

    Page(s): 25 - 29
    Save to Project icon | PDF file iconPDF (131 KB)  

    We present an analysis of the steady state optical response of two‐dimensional optical superlattices with Kerr nonlinearity. We consider the effects of the modification of the refractive index modulation strengths in the superlattices and the angular deviation of incoming radiation from Bragg conditions. We find that under Bragg incidence the system displays optical bistability only when the modulation ratio exceeds a certain threshold. We also predict that optical bistability can disappear under non‐Bragg incidence. Physical considerations are presented and discussed on how to optimize the chances for observing optical bistability in such a superlattice. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Adhesive contact of cylindrical lens and a flat sheet

    Page(s): 30 - 37
    Save to Project icon | PDF file iconPDF (202 KB)  

    Methods are developed to estimate the adhesion and surface free energies of compliant materials from the contact deformations of cylindrical lenses with flat sheets. Some important differences are found between the cylindrical contact studied here and the widely studied geometry of spherical contact. For example, while the pull‐off force is completely independent of the elastic constants (K) of the materials for spherical contacts, the pull‐off force for cylindrical contact is proportional to K1/3. Furthermore, for cylindrical contacts the contact width at separation reaches to a value of 39% of the width (a0) at zero load, whereas the corresponding value is 0.63a0 for spherical contact. The feasibility of using cylindrical contacts to estimate the surface and adhesive energies of polymers was investigated using elastomeric polydimethylsiloxane (PDMS) as a model system. PDMS was used in two ways: (1) unmodified and (2) with its surface hydrolyzed with dilute hydrochloric acid. Significant hysteresis of adhesion was observed with the hydrolyzed PDMS surfaces due to H‐bonding interactions, which appeared to depend on normal stress. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Thermal and electrodynamic effects in melting current‐carrying conductors

    Page(s): 38 - 45
    Save to Project icon | PDF file iconPDF (194 KB)  

    This work studies dynamics of melting in current‐carrying conductors. It is shown that during equilibrium melting, when the dynamics of a phase‐transition front are determined by a heat balance, there exists a single‐valued correlation between the rate of inductance change and a temperature at the phase‐transition front. It is demonstrated that, although surface melting begins at temperatures less than the melting temperature of the current‐free conductor, corrugation of a phase‐transition front occurs at this temperature. It is shown that the nucleation rate of nuclei flattened in the direction normal to a conductor’s axis is negligibly small. Current dynamics at the stage of melting are analyzed for the case of a fixed external voltage. It is demonstrated that there exists an instability stage at which an excitation of the electric current occurs. Conditions for the experimental observation of the predicted phenomena are discussed. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Experimental investigation and characterization of the departure from local thermodynamic equilibrium along a surface‐wave‐sustained discharge at atmospheric pressure

    Page(s): 46 - 55
    Save to Project icon | PDF file iconPDF (207 KB)  

    Surface‐wave‐sustained discharges (SWDs) form a particular class of high frequency (HF) discharges: their HF sustaining field is provided by a traveling wave that transfers energy as it propagates along the discharge column, yielding a plasma column with an axially decreasing electron density. SWDs have proved to be ideal for investigating experimentally and theoretically both the HF field and discharge aspects of HF plasma sources at reduced gas pressure. In this article, SWDs are utilized at atmospheric pressure to gain insight into the departure from thermodynamic equilibrium (TE) of HF sustained discharges. This departure is found to increase significantly as the electron density decreases along the plasma column whereas the gas temperature and the power absorbed per electron do not vary axially. The two‐temperature plasma model provides an adequate description of this departure from TE. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Ion energy distributions in SF6 plasmas at a radio‐frequency powered electrode

    Page(s): 56 - 65
    Save to Project icon | PDF file iconPDF (275 KB)  

    An energy‐resolving quadrupole mass spectrometer (E‐QMS) was assembled underneath the powered electrode of a diode reactive ion etcher. The plasma ions reach the E‐QMS through an orifice in the powered electrode with a diameter of 100 μm. The ion energy distributions (IEDs) of ionic species from SF6 plasmas in the pressure range of 0.1–1.5 Pa for dc bias potentials between 50 and 300 V and a rf of 13.56 MHz were investigated. The IEDs always show a saddle shaped peak at an energy corresponding to a total potential drop across the sheath given by USh=Udc+UP, where Udc is the dc bias potential and UP is the time averaged plasma potential. In the energy range from 0 eV to eUdc there are multiple peaks in the IEDs of SF+x (x=1..5), whereas the F+, F+2, and S+ IEDs show only a single peak in this range. These peaks are the result of ion generating collisions in the sheath. On pressure variation the IEDs do not change significantly. We also measure IEDs of negative ions. The IEDs of these ions show a broad distribution with an intensity maximum appearing at the half of UP and a width corresponding to max[UP(t)], where UP(t) is the time varying plasma potential. These correlations suggest that these ions originate from the plasma bulk. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Sheath expansion into a large bore

    Page(s): 66 - 69
    Save to Project icon | PDF file iconPDF (137 KB)  

    Sheath expansion into a cylindrical bore is studied for radii larger than the ion‐matrix overlap radius in the context of plasma‐based ion implantation. The temporal dependence of the sheath width, sheath speed, and ion impact energy and the dependence of the maximum and average ion impact energy on the radius of the bore are computed. It is found that the sheath speed increases as the radii decreases, and that it is, in all cases, greater than the planar sheath speed. After the sheath has reached the axis, the potential drop across the bore decays rapidly. Consequently, the ion impact energy first increases and then decreases in time. Both the maximum and average impact energy increase with radius. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Site‐selective chemical‐vapor‐deposition of submicron‐wide conducting polypyrrole films: Morphological investigations with the scanning electron and the atomic force microscope

    Page(s): 70 - 75
    Save to Project icon | PDF file iconPDF (2556 KB)  

    We report morphological investigations of polypyrrole thin films deposited by means of a self‐aligning vapor phase technique onto glass, silicon and silicon dioxide substrates, coated with an oxidizing precursor. The variation of the deposition parameters allows the control of the film microstructure which can be fibrillar and strongly anisotropic or globular and tendentially isotropic. Patterning of the precursor by electron‐beam lithography allows the production of submicron wide lines as shown by both the scanning electron microscope and the atomic force microscope. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Magnetic entropy in nanocomposite binary gadolinium alloys

    Page(s): 76 - 80
    Save to Project icon | PDF file iconPDF (97 KB)  

    Investigation on magnetocaloric effects, magnetic entropy, Curie temperature, and specific heat of nanocomposite binary gadolinium alloys Gd–Tb, Gd–Zn, and Gd–Y has been carried out with an applied magnetic field of 1 T and in a temperature range of 233–313 K. Compared with the respective bulk alloys, the as‐prepared nanocomposite alloys were found to have higher specific heat and lower Curie temperature. The nanocomposite Gd–Y alloy exhibited distinctive enhancement of both magnetocaloric effect and magnetic entropy over that of the bulk alloy. The finding is of importance for developing new materials for magnetic refrigeration at room temperature. A discussion concerning the enhanced magnetic entropy in nanometer superparamagnetic systems is presented in detail. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Strain and structural characterization of Zn1-xCdxSe laser structures grown on GaAs and InGaAs (001) substrates

    Page(s): 81 - 88
    Save to Project icon | PDF file iconPDF (228 KB)  

    X‐ray reciprocal space mapping has been used to investigate the strain status of microgun‐pumped blue and blue‐green laser structures. The devices exploit graded‐index, separate confinement Zn1-xCdxSe/ZnSe heterostructures grown on InGaAs or GaAs substrates by molecular‐beam epitaxy. The location of the reciprocal lattice point of the ZnSe buffer layer within a normally forbidden region of reciprocal space indicates that the ZnSe buffer layer is unusually strained, with an appreciable biaxial tensile strain despite the smaller lattice parameter of the III–V substrate relative to ZnSe. We associate such a phenomenon with the presence of the highly strained laser structure coupled with preferential strain relaxation at the II–VI/III–V heterointerface. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Unique x‐ray diffraction pattern at grazing incidence from misfit dislocations in SiGe thin films

    Page(s): 89 - 96
    Save to Project icon | PDF file iconPDF (153 KB)  

    Grazing‐incidence x‐ray diffraction (GIXD) permits the direct measurement of in‐plane lattice parameters of SiGe films that are too thin to yield good results from normal‐geometry triple‐axis techniques. A unique ‘‘X’’‐shaped pattern has been seen in H–K reciprocal space maps of diffracted x‐ray intensity from SiGe films that have relaxed via a modified Frank–Read mechanism. Contours of intensity are seen along the 〈110〉 directions from the (4¯00) reciprocal lattice peak with the introduction of the first dislocations. For higher dislocation densities the X‐shaped contours are anisotropically distorted and a satellite peak, corresponding to the lattice parameter for a partially relaxed film, becomes identifiable at lower H. In contrast, H–K reciprocal‐space contours from thin SiGe films that have relaxed by roughening and subsequent random nucleation of dislocations display broad, oval‐shaped contours centered at the (4¯00) reciprocal lattice point for the film. Numeric simulations of GIXD from a variety of dislocation arrangements were performed in order to understand the origin of the X pattern. We show that this pattern arises from an array of long misfit dislocations running in the 〈110〉 directions. The anisotropic distortion of the X pattern arises at higher dislocation densities from orthogonal intersections of dislocations with equal Burgers vector, which are characteristic of dislocation networks generated by the modified Frank–Read mechanism. We also verify that the measured values of the in‐plane lattice parameter, together with the out‐of‐plane lattice parameter determined from the symmetric (004) reflection, lead to accurate calculation of the composition and strain in these SiGe layers. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Role of Si–H bonding in a‐Si:H metastability

    Page(s): 97 - 102
    Save to Project icon | PDF file iconPDF (125 KB)  

    In plasma‐deposited a‐Si:H films, the time dependence and saturation value of the metastable defect density produced by high‐intensity illumination are found to depend on the material properties. From a wide range of deposition techniques, we have observed a strong correlation between the steady‐state defect density Nss and the monohydride Si–H bond concentration observed in infrared transmission, with [SiH]2000 values between 2% and 16%. We propose a microscopic description of the light‐induced defect creation and light‐induced defect annealing phenomena in a‐Si:H, based on the trapping of mobile H at two specific sites: the Si–H bond and the Si dangling bond. This model predicts a steady‐state defect density proportional to the monohydride [SiH]. For the production of mobile H in three‐center (Si–H–Si) configurations, a low‐energy mechanism with no necessity for Si–H bond breaking is suggested from the observed changes in the infrared absorption of the various H‐bonding configurations during light soaking. With the assistance of an electron‐hole pair recombination, it consists of the excitation of two adjacent H atoms from a (Si–H H–Si) configuration along with a Si–Si bond reconstruction. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Preparation and properties of ferromagnetic carbon‐coated Fe, Co, and Ni nanoparticles

    Page(s): 103 - 108
    Save to Project icon | PDF file iconPDF (902 KB)  

    Carbon‐coated iron, cobalt, and nickel particles were produced by an arc discharge process modified in the geometry of the anode and the flow pattern of helium gas. Field emission scanning electron microscopy shows that the resulting material consists of only carbon‐coated metal particles without any nanotubes or other unwanted carbon formations present. The diameters of iron, cobalt, and nickel particles range predominantly from 32 to 81 nm, 22 to 64 nm, and 16 to 51 nm, respectively. X‐ray diffraction analysis confirmed that the as‐made particles are carbon‐coated elements rather than metal carbides. High resolution transmission electron microscopy reveals that the as‐made cobalt and nickel particles are covered by 1–2 graphitic layers, while iron particles are surrounded by amorphous carbon. When the samples were treated by annealing or immersion into nitric acid, particles completely coated by carbon resisted both postdeposition treatments. However, further graphitization of the carbon coating by either of the two treatments was observed. Particles only partially coated by carbon were not protected, but sintered by annealing or dissolved in the acid. The magnetic properties of the as‐made particles were measured by a vibrating sample magnetometer. The values of the saturation magnetic moment per gram of each type of metal particle are 56.21, 114.13, and 34.9 emu/g representing 26%, 71%, and 64% of the saturation moments of the bulk ferromagnetic elements iron, cobalt, and nickel, respectively. All the metal particles were shown to be ferromagnetic with a ratio of remnant to saturation magnetization MR/MS∼0.3 at room temperature (25 °C). In this article the detailed preparation and the properties of these carbon‐coated metal particles will be discussed. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Hydrogen determination in Si‐rich oxide thin films

    Page(s): 109 - 114
    Save to Project icon | PDF file iconPDF (110 KB)  

    Quantitative in‐depth distribution of the elements contained in silicon‐rich oxide thin films deposited on single‐crystal silicon by low temperature plasma‐assisted deposition has been performed by a combination of various MeV ion beam techniques. The quantity of oxygen and nitrogen has been measured by nuclear reactions, the silicon content has been determined by Rutherford backscattering, and elastic recoil detection was used for hydrogen. All the samples contain not only Si and O, but also N and H, which are residuals from the reactions involved in the deposition process. We did find that the MeV beam used in the nuclear techniques can induce a process of hydrogen desorption, which causes the measured H content to be a function of the He dose received by the sample. This phenomenon, not previously reported, must be taken into account to give the correct H content. The study of the kinetics of the He‐induced hydrogen desorption has been used to correct the experimental data and to determine the original hydrogen content. The correction factor is in most of the cases close to 2 and outside any experimental error. Moreover the studies of the kinetics give information on the kinds of hydrogen complexes contained in the films. The results suggest that, on the basis of the strength of the binding energies, hydrogen is present in at least two different configurations, weakly and strongly bonded. In the first configuration hydrogen is easily desorbed either under the action of the ion beam or of the heat treatment at 600 °C, in the second, hydrogen is lost only after treatment at 900 °C. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Cholesteric liquid‐crystal displays illuminated by diffuse and partially diffuse light

    Page(s): 115 - 121
    Save to Project icon | PDF file iconPDF (157 KB)  

    We report on the photometric and colorimetric properties of surface and polymer network stabilized reflective cholesteric displays. Both diffuse and partially diffuse illumination are used, the latter being an experimental approach to emulating typical room light conditions. It is shown that addition of polymer increases the field of view while decreasing angular dependence of the color quantities: hue, chroma, and lightness. Total luminance and contrast ratio, however, are also decreased. Therefore, it is concluded that optimum polymer concentration is dependent on the viewing geometry. Luminance and contrast ratio of the surface stabilized cells exceeded that of polymer stabilized cell when viewed in a geometry void of specular reflection. Colorimetric quantities in surface stabilized cells are less sensitive to illumination geometry. This suggests that for displays in which specular reflection has been suppressed, surface treatment represents the best method of stabilization. If the viewing angle allows specular reflection, polymer stabilization yields the largest luminance and contrast ratio. This behavior is explained in terms of angular distribution of helical axes due to presence of the stabilizer. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An experimental study on the shear viscosity of solids

    Page(s): 122 - 130
    Save to Project icon | PDF file iconPDF (188 KB)  

    Viscoelastic solids with high viscosity were experimentally studied with the intention of having them deformed under uniform shear stress. A kind of sandwich method was developed for applying a constant shear stress to a specimen, and its deformation was observed optically using heterodyne interferometry with a sensitivity of 10 nm in displacement measurement. Time‐dependent deformation data were analyzed on the basis of a mechanical model of anelasticity plus viscosity. Viscosity in the range of 108–1014 Pa∙s could be determined at temperatures of 20–200 °C. Through a simulation using the finite element method together with an experiment visualizing the deformation, the specimen deformation was shown to be of an almost uniform shear mode. Experiments were performed to determine the temperature dependence of viscosity for several kinds of glasses near their glass transition Tg, and the determined viscosity values were about 107 Pa∙s at Tg. The viscosity values measured by a rotation disk viscometer were in good agreement with the present data. The viscosity of some glasses was also measured by the beam bending and penetration methods, and values of 109–1012 Pa∙s at Tg were obtained. The large discrepancy between the two kinds of data was considered. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optical switching in polymer gels

    Page(s): 131 - 136
    Save to Project icon | PDF file iconPDF (5198 KB)  

    Soft materials have long been sought after for use in devices such as actuators, artificial muscles, separators, switches, sensors, memories, and so forth. We developed a soft, optically transparent material using polymer gels that can not only be activated by visible light (switched on) but also deactivated (switched off) by altering the local environment using three different means: pH, temperature, and light. This copolymer gel is a covalently cross‐linked network of N‐isopropylacrylamide, sodium acrylate, and a chromophore, which is found to undergo phase transitions exhibiting large hysteresis in the degree of swelling in response to pH, temperature, and light. In each system, between the transitions for swelling and shrinking, the gel can show either a swollen or a collapsed state, which can be selected according to the history of the variables. It has been established that a thermoresponsive gel with chromophore exhibits a local volume phase transition upon illumination with visible light. By making use of this phenomenon, we have successfully controlled the phase in which a gel exists with visible light: Without light illumination the gel stays in the swollen state. Upon illumination beyond a threshold intensity, however, a volume transition is locally induced, thereby forming a material in which both phases coexist stably for at least several hours after the light source has been removed. The phenomenological stability of the material in the coexistence state is discussed on the basis of the Landau theory. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Phase diagram of HgTe–ZnTe pseudobinary and density, heat capacity, and enthalpy of mixing of Hg1-xZnxTe pseudobinary melts

    Page(s): 137 - 142
    Save to Project icon | PDF file iconPDF (127 KB)  

    In this article, the solidus temperatures of the Hg1-xZnxTe pseudobinary phase diagram for several compositions in the low x region were measured by differential thermal analysis and the HgTe–ZnTe pseudobinary phase diagram was constructed. The densities of two HgZnTe melts, x=0.10 and 0.16, were determined by an in situ pycnometric technique in a transparent furnace over, respectively, 110 and 50 °C ranges of temperature. The thermodynamic properties of the melts, such as the heat capacity and enthalpy of mixing, were calculated for temperatures between the liquidus and 1500 °C by assuming an associated solution model for the liquid phase. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Non‐linear resistance behavior in the early stages and after electromigration in Al‐Si lines

    Page(s): 143 - 150
    Save to Project icon | PDF file iconPDF (181 KB)  

    A common result obtained in electromigration experiments carried out on Al‐Si lines using different high resolution resistometric methods, is a monotonous non‐linear resistance increase at the very beginning of the high current electromigration test, and a decrease after the high stressing current is switched off. These effects have often been attributed to the attainment of a steady state of vacancy concentration during and after electromigration. This paper shows how even small abrupt temperature steps, always present at the beginning and after electromigration tests, are the triggering events for different, often reversible, physical phenomena contributing to non‐linear resistance changes. Precipitation–dissolution of alloyed elements appears to be the most significant one. Abrupt temperature changes also induce a change of the hydrostatic stress of passivated lines. The relaxation of the hydrostatic stress could be coupled with a void volume change, and the total resistance is a function of both the hydrostatic stress (through resistivity) and of void volume. However, we demonstrate that in our experiments the effect of hydrostatic stress relaxation on resistance variations is negligible with respect to the action of precipitation–dissolution. These non‐linear, thermally induced effects, however, do not exclude possible simultaneous resistance changes due to the accumulation/relaxation of the electromigration damage. Experimental results are collected by means of different, complementary techniques. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Charge state control of hydrogenation in silicon

    Page(s): 151 - 155
    Save to Project icon | PDF file iconPDF (298 KB)  

    We demonstrate that periodic exposure to zero bias during in situ hydrogenation of reverse‐biased p‐type Schottky barrier structures has dramatic effects on H penetration. H influx can be slowed or even stopped by such protocols. By contrast, similar pulsing techniques produce almost no changes of penetration in n‐type barriers during hydrogenation; this latter observation is in sharp contrast to the expectations that charge conversion from H+ to H- would reverse the drift of H species. We suggest that these effects are caused by the charge conversion of relatively immobile H‐related defects. In the p‐type barriers this results in a weakening or reversal of the near surface electric field, effectively stopping the drift of H+ into the bulk. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The effect of excess gallium vacancies in low‐temperature GaAs/AlAs/GaAs:Si heterostructures

    Page(s): 156 - 160
    Save to Project icon | PDF file iconPDF (557 KB)  

    This article shows that the presence of low‐temperature‐grown GaAs (LT‐GaAs) in LT‐GaAs/AlAs/GaAs:Si heterostructures increases the Al/Ga interdiffusion at the heterostructure interfaces. The interdiffusion enhancement is attributed to the presence of Ga vacancies (VGa) in the As‐rich LT‐GaAs, which diffuses from a supersaturation of VGa frozen‐in during sample growth. Chemical mapping, which distinguishes between the AlAs and GaAs lattices at an atomic scale, is used to measure the Al concentration gradient in adjacent GaAs:Si layers. A correlation is observed between the Al/Ga interdiffusion and the gate breakdown voltage in metal‐insulator field‐effect transistor structures containing LT‐GaAs. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Kinetics and thermodynamics constraints in Pt gettering by P diffusion in Si

    Page(s): 161 - 166
    Save to Project icon | PDF file iconPDF (159 KB)  

    We have explored the mechanisms underlying the gettering of Pt atoms dissolved in crystalline Si. By using Pt implantation at different fluences followed by a thermal process at 970 °C for 5 h we were able to prepare crystalline silicon wafers containing a uniform Pt concentration in the range 2×1012–2×1014 atoms/cm3. Subsequently, a heavily doped n‐type region was produced on one side of the wafer by P diffusion at 900 °C. Following this deposition process we have studied the kinetics of Pt gettering to the P‐doped region in the temperature range 700–970 °C and for annealing times ranging from 30 min to 48 h. Lifetime measurements by means of a contactless technique were used to detect the depletion of Pt in the bulk of the wafer due to the gettering process. The large range of initial Pt concentrations that we have explored allowed us to identify and separate the kinetics and thermodynamics constraints that determine the gettering efficiency and to propose a phenomenological model for the gettering of Pt. In particular, it has been found that the kinetics of the gettering process are driven by the dissolution of immobile substitutional Pt atoms into interstitial sites. This process is assisted by Si self‐interstitials and characterized by an activation energy of 0.4 eV. Moreover, the equilibrium distribution of Pt is thermodynamically determined by a segregation coefficient of the Pt atoms between the gettering sites and the silicon matrix. This segregation coefficient, and hence the gettering efficiency, decrease when the temperature of the gettering process is increased and is described by an activation energy of 2.5 eV. © 1996 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

Full Aims & Scope

Meet Our Editors

Editor
P. James Viccaro
Argonne National Laboratory