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Applied Physics Letters

Issue 18 • Date May 1995

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Displaying Results 1 - 25 of 46
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Micromachined submicrometer photodiode for scanning probe microscopy

    Page(s): 2309 - 2311
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    A submicrometer photodiode probe with a sub‐50 nanometer tip radius has been developed for optical surface characterization on a nanometer scale. The nanoprobe is built to detect subwavelength optical intensity variations in the near field of an illuminated surface. The probe consists of an Al–Si Schottky diode constructed near the end of a micromachined pyramidal silicon tip. The process for batch fabrication of the nanoprobes is described. Electrical and optical characterization measurements of the nanoprobe are presented. The diode has a submicrometer optically sensitive area with a 150 fW sensitivity. © 1995 American Institute of Physics. View full abstract»

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  • New phase‐change rewritable optical recording film having well suppressed material flow for repeated rewriting

    Page(s): 2312 - 2314
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    Characteristics of a phase‐change optical disk using a (Ge–Sb–Te)‐(Cr–Te) recording film containing a high‐melting‐point component Cr–Te are studied. The high‐melting‐point component Cr–Te precipitates in the recording film, and prevents a material flow of the recording film during repeated rewrites in which the recording film is melted. There is no drawback such as noise increase by the addition of Cr–Te. Thus the phase‐change optical disk using this recording film shows very small distortion in the reproduced signal wave form even after 2×104 rewrites of high‐density recording signals that are liable to cause the material flow by forming long and short recording marks on the disk. With a phase‐change optical disk, it is easy to overwrite (rewrite without prior erasure) information, which makes it highly suitable for digital recording of motion pictures and sound. They are expected to be used as rewritable compact disks, rewritable CD‐ROM disks, rewritable video disks, and small recording media for personal computers. © 1995 American Institute of Physics. View full abstract»

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  • Superior output linearity of optimized double heterostructure vertical‐cavity top‐emitting lasers

    Page(s): 2315 - 2317
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    Optimized double heterostructure (DH) vertical‐cavity top‐emitting lasers are grown by molecular beam epitaxy. Both the doping profile and the laser structure are optimized to achieve high performance. Continuous wave 2 mW output power at room temperature is obtained for nominal 10 μm diam DH vertical‐cavity top‐emitting injection lasers. A single fundamental longitudinal and transverse mode is maintained up to 1.7 mW. It lases in continuous waves at a temperature of 80 °C. A lasing power range of ∼0.8 mW is sustained within a 10% change in the output linearity, which is much larger than a value of less than 0.1 mW for quantum well lasers. This demonstrates that its output linearity is far more superior than the one of compared quantum well lasers, which is explained in detail. © 1995 American Institute of Physics. View full abstract»

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  • All solid state laser source for tunable blue and ultraviolet radiation

    Page(s): 2318 - 2320
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    Tunable blue and ultraviolet single mode laser light has been generated by frequency quadrupling the output of a semiconductor laser with two successive frequency doubling stages. The laser source is based on a commercial high power semiconductor laser near 972 nm which combines a low power single mode master oscillator with a high power amplifier. The doubling stages consist of nonlinear crystals which are placed inside compact optical buildup resonators. Up to 156 mW tunable blue radiation near 486 nm and 2.1 mW ultraviolet light near 243 nm have been produced. © 1995 American Institute of Physics. View full abstract»

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  • Photoluminescence imaging of porous silicon using a confocal scanning laser macroscope/microscope

    Page(s): 2321 - 2323
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    This letter describes a confocal scanning beam macroscope/microscope that can image specimens up to 7 cm in diameter using both photoluminescence and reflected light. The macroscope generates digital images (512×512 pixels) with a maximum 5 μm lateral resolution and 200 μm axial resolution in under 5 s, and in combination with a conventional confocal scanning laser microscope can provide quality control at a macroscopic/microscopic level for porous silicon specimens, wafers, detectors, and similar devices. This combination of instruments can also be used as a method for evaluating preparation parameters involved in the manufacture of porous silicon. Various confocal and nonconfocal photoluminescence and reflected‐light images of porous silicon are shown using both a macroscope and a conventional confocal scanning laser microscope. A 3D profile of a porous silicon structure reconstructed from confocal slices is also shown. © 1995 American Institute of Physics. View full abstract»

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  • Thin‐film nonlinear optical diode

    Page(s): 2324 - 2326
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    We present results of a theoretical investigation into a nonlinear thin‐film multilayer device that exhibits passive anisotropic optical transmission—the analogue of the electronic diode. This optical diode is a nonlinear, asymmetric, distributed Bragg reflector. Material parameters for a nonlinear polymer (polydiacetylene 9‐BCMU) and rutile are used in alternating layers to model a realistic device. The diode exhibits more than five times as much transmittance in one direction as in the opposite direction. It has a thickness of only 2 μm and is polarization insensitive. © 1995 American Institute of Physics. View full abstract»

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  • Origin of scintillation in cerium‐doped oxide crystals

    Page(s): 2327 - 2328
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    We propose here a model of the scintillation from complex oxide single crystals doped with Ce3+ ions to explain the correlation observed between scintillation light yield and intrinsic luminescence of the matrix. © 1995 American Institute of Physics. View full abstract»

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  • Practical definition of the plasma sheath edge for modeling planar glow discharges

    Page(s): 2329 - 2330
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    While the parallel‐plate capacitive model is often employed to describe the electrical behavior of a plasma sheath, the simple question of how far apart the two plates are for a given plasma cannot be easily answered yet because of the lack of a workable definition of the sheath edge. The sheath edge estimated with the Child–Langmuir equation may misplace as much as 40% of the total space charge outside the sheath. An alternative practical definition of the sheath edge is proposed that includes almost all space charge within the sheath. © 1995 American Institute of Physics. View full abstract»

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  • Atomic resolution ultrahigh vacuum scanning tunneling microscopy of epitaxial diamond (100) films

    Page(s): 2331 - 2333
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    We report atomic resolution images of chemical vapor deposition grown epitaxial diamond (100) films obtained in ultrahigh vacuum (UHV) with a scanning tunneling microscope. A (2×1) dimer surface reconstruction and amorphous atomic regions are observed. The (2×1) unit cell is measured to be 0.51±0.01×0.25±0.01 nm2. The amorphous regions are identified as amorphous carbon. A radial structure 1.5 nm in diameter is observed on a plane at a 20° slope to the (2×1) surface. Tunneling current versus voltage spectra in UHV and Raman spectra are also obtained. © 1995 American Institute of Physics. View full abstract»

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  • Rapid densification of porous carbon–carbon composites by thermal‐gradient chemical vapor infiltration

    Page(s): 2334 - 2336
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    Porous carbon–carbon preforms, 10.8 cm o.d.×4.4 cm i.d.×3.0 cm thick have been densified in a one‐cycle, 26 h process. The disks are heated by induction, creating an inside‐out thermal gradient, and are exposed to cyclopentane vapor in a water‐cooled vacuum chamber. Rough‐laminar carbon microstructure is obtained; a compressive strength of 268 MPa is measured at 1.79 g/ cm3 density. The densification rate is monitored in real time. The precursor utilization efficiency is 20%–30%. Our patented process can be applied to other materials, has significant scale‐up potential and is economically competitive. © 1995 American Institute of Physics. View full abstract»

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  • Three‐dimensional morphology of a very rough interface formed in the soldering reaction between eutectic SnPb and Cu

    Page(s): 2337 - 2339
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    We have used scanning electron microscopy to study the interfacial morphology of the Cu‐Sn compounds formed between a eutectic SnPb alloy and Cu at 200 °C. A selective etching reveals the three‐dimensional morphology of the Cu‐Sn compounds. On the solder side, the compounds grow rapidly as big scallops and the interface becomes extremely rough as compared to the Cu side of the interface. In order to understand this rapid and extremely irregular growth of the Cu‐Sn compounds, we propose that it is caused by the dissolution of Cu into the liquid solder and the coarsening of the scallop‐type compounds by Ostwald ripening. The growth of the Cu‐Sn compounds has a serious impact on solder joint rework in electronic packaging. © 1995 American Institute of Physics. View full abstract»

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  • Comparison of trapping–detrapping properties of mobile charge in alkali contaminated metal‐oxide‐silicon carbide structures

    Page(s): 2340 - 2342
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    We have performed thermally stimulated ionic current measurements on aluminum‐oxide‐silicon carbide (3C and 6H polytypes) capacitors to study the trapping–detrapping properties of alkali mobile ions at the oxide interfaces. Two traps, at ∼1.0 and ∼1.4 eV, have been detected at the oxide/SiC interface; only one (at ∼1.0 eV) is present at the aluminum/oxide interface. Studies of the energy dependence of the oxide traps with the electric field are reported here for comparison with silicon structures. A numerical method has been used to calculate the energy distributions of these traps, which reveal some differences between the two kinds of structures. © 1995 American Institute of Physics. View full abstract»

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  • Mössbauer study of the (Fe1-xNix)4N compounds (0≤x≤0.6)

    Page(s): 2343 - 2345
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    Single phase γ’‐Fe4N type (Fe1-xNix)4N compounds (0≤x≤0.6) have been synthesized by heating iron‐nickel oxalates under a mixture stream of NH3 and H2. The compounds were investigated by x‐ray diffraction and Mössbauer spectroscopy. The results confirm that the lattice constants decrease with increasing content of nickel. Compared with the same compositional Fe1-xNix alloys, the average expansion of the unit cell (δV/V) is 16.7% for γ‐Fe‐Ni alloys. The Mössbauer study shows that the substitution of nickel atoms for iron atoms has a tendency to locate at the corner sites. When x=0.5, all of the corner sites are completely occupied by nickel atoms. © 1995 American Institute of Physics. View full abstract»

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  • Comparison of surface roughness of polished silicon wafers measured by light scattering topography, soft‐x‐ray scattering, and atomic‐force microscopy

    Page(s): 2346 - 2348
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    The surface roughness of silicon wafers after different stages of chemomechanical polishing was investigated by light scattering topography, soft‐x‐ray scattering, and atomic‐force microscopy. Quantitative values of the rms roughness, the lateral correlation length, and the roughness exponent are extracted. The results suggest deviations from the ‘‘ideal’’ polishing process at large length scales. © 1995 American Institute of Physics. View full abstract»

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  • Depth correlated lateral variations of layer thicknesses in GaAs‐AlGaAs multiple quantum wells investigated by cathodoluminescence

    Page(s): 2349 - 2351
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    Lateral variations of the exciton confinement energy Ecx have been investigated in a GaAs‐AlGaAs multiple quantum well (MQW) structure using cathodoluminescence (CL) imaging in a scanning electron microscope. The MQW structure was grown by molecular beam epitaxy on a 2° misoriented GaAs substrate. The CL image of a defined MQW region does not change its lateral intensity distribution after removing different numbers of quantum wells by etching, indicating a correlated variation of Ecx between different quantum wells on a length scale of several μm. The variation of Ecx is connected to a mound like surface topography. © 1995 American Institute of Physics. View full abstract»

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  • Suppressed gate current in a superlattice‐insulated‐gate field‐effect transistor on InP

    Page(s): 2352 - 2354
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    A new insulating layer is used in a normally‐off (i.e., enhancement‐mode) field‐effect transistor on an InP substrate. It consists of closely spaced, strained AlAs barriers embedded in In0.52Al0.48As between the In0.53Al0.47As channel and the metal gate. This insulating layer increases the forward‐bias gate turn‐on voltage by approximately 50% and reduces the gate leakage current by as much as 50 times compared to a conventional In0.52Al0.48As insulating layer. In addition, the transistor characteristics are significantly improved such that the maximum current is increased approximately three times and the peak transconductance is increased by 70%. These properties are explained by superior confinement of electrons to the channel in the presence of the AlAs barriers. © 1995 American Institute of Physics. View full abstract»

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  • In situ monitoring of internal surface area during the growth of porous silicon

    Page(s): 2355 - 2357
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    A novel and convenient method of monitoring the internal surface area of a porous silicon layer formed on an n‐type substrate has been developed. The technique has been employed during electrochemical growth and subsequent chemical leaching of porous silicon layers in hydrofluoric acid/ethanol. The method involves periodic interruption of the anodization current to allow in situ measurement of the interfacial capacitance under forward bias using a triangular voltage wave form. The observed evolution of the internal surface area is related to the development of photoluminescence. © 1995 American Institute of Physics. View full abstract»

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  • On the origin of oval defects in metalorganic molecular beam epitaxy of InP

    Page(s): 2358 - 2360
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    We have studied the dependence of oval‐shaped defects on growth conditions during metalorganic molecular beam epitaxy of InP. The density of oval defects is independent of growth conditions but strongly dependent on the initial substrate surface preparation. Contaminants existing on the surface prior to growth are indicated as the likely cause of oval defect formation due to local enhancement of metalorganic molecules cracking on the surface and the subsequent formation of group III rich structures. High densities of such defects are shown to degrade the optical properties of InGaAs quantum wells. © 1995 American Institute of Physics. View full abstract»

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  • Electronic noise of submicron n+nn+ diodes under near‐oscillatory macroscopic behaviors

    Page(s): 2361 - 2363
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    We present a theoretical investigation on the electronic noise of submicron n+nn+ GaAs diode under the conditions when the electrical characteristics of the diode exhibit a pronounced near‐oscillatory macroscopic behavior caused by velocity fluctuations of single particles at the microscopic level. Two kinds of spontaneous oscillations, related to transit time and plasma oscillations, and their contributions to the diode noise are investigated by a Monte Carlo simulation. A simple analytical model which provides an excellent fit of the macroscopic features of the noise obtained by the Monte Carlo simulation is developed. © 1995 American Institute of Physics. View full abstract»

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  • Strain‐induced quantum dots by self‐organized stressors

    Page(s): 2364 - 2366
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    Novel in situ method to produce quantum dots is reported. Three‐dimensional confinement of carriers to a GaInAs/GaAs quantum well dots is observed by photoluminescence. The confinement potential is induced by stressors, formed by self‐organizing growth of InP nanoscale islands on top barrier GaAs surface. Two transitions arising from the strain‐induced quantum dots produced by two types of InP islands are identified. The luminescence from higher electronic states of the quantum dots having a level splitting of 8 meV is also observed. © 1995 American Institute of Physics.   View full abstract»

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  • Identification of individual bistable defects in avalanche photodiodes

    Page(s): 2367 - 2369
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    The effects of individual bistable defects on the dark counting rate of avalanche photodiodes have been monitored and their temperature dependence studied. The presence of a bistable defect in the diode is indicated by the repeated random switching of the counting rate between two well‐defined rates. Four of the defects studied were produced via reaction with a single neutron from a Be–Am source, while two were found to exist without irradiation. Results were analyzed in terms of the activation energies of the electron generating capabilities of the defects, and the effective potential barriers between the two structural configurations of the bistable states. Among the six defects studied, two of them could be of the same type. © 1995 American Institute of Physics. View full abstract»

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  • Recoil implantation of radioactive transition metals and their investigation in silicon by deep‐level transient spectroscopy

    Page(s): 2370 - 2372
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    Radioactive isotopes are produced by nuclear reactions in a thin target foil. The recoiling products are directly implanted into samples mounted off‐axis to the primary beam. Using proton or α beams and appropriate target foils, radioactive isotopes of Ti, V, Cr, Mn, and Co were implanted. The implantation parameters are presented and compared with other implantation techniques for radioactive isotopes. To demonstrate an application, a deep‐level transient spectroscopy measurement on 48V in silicon is presented. Ti and V correlated band‐gap levels were observed during the 48V decay. © 1995 American Institute of Physics. View full abstract»

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  • Crystalline quality of strain‐free GaAs‐on‐Si structures formed by annealing under ultrahigh pressure

    Page(s): 2373 - 2375
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    Crystalline quality and residual strain in GaAs films epitaxially grown on Si substrates have been investigated after annealing them under ultrahigh pressures up to 2.1 GPa. The strain in the films decreased linearly with increase of pressure and it became zero at a pressure around 1.9 GPa. The strain depended weakly on the annealing temperature in the range from 300 to 500 °C. A slight increase in the channeling minimum yield in Rutherford backscattering spectrometry was observed in the samples with broad‐area GaAs films. However, the degradation in the crystalline quality was avoided by etching the GaAs films in a stripe pattern with 10 μm width. © 1995 American Institute of Physics. View full abstract»

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  • Kinetics of interdiffusion in strained nanometer period Si/Ge superlattices studied by Raman scattering

    Page(s): 2376 - 2378
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    Intermixing time ti and interdiffusion coefficients D of nanometer periods Si/Ge strained layer superlattices (SLSs) were measured by Raman scattering technique. Si12Ge12 and Si19Ge9 SLSs have been annealed in the temperature range 760–900 °C during various time intervals. The observed D and ti follow the Arrhenius‐like behavior with different activation energies ΔE=1.78±0.15 eV and 3.94±0.15 eV and pre‐exponential factors D=2×10-10 cm2 s-1 and 0.7 cm2 s-1, respectively, for the Si12Ge12 and Si19Ge9 SLSs. D, ti, ΔE, and D0 are strongly affected by the changes of the SLS layer thickness, and strain. An explanation of the experimental observations is proposed in terms of the kinetic electron‐related theory of atomic diffusion in solids. The observed variations of ΔE and D0 are related to the material parameters, which are characterized by picosecond atomic and electronic phenomena in nanometer regions, in good agreement with the observations. © 1995 American Institute of Physics. View full abstract»

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Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics.

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Nghi Q. Lam
Argonne National Laboratory