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Applied Physics Letters

Issue 23 • Date Jun 1995

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Displaying Results 1 - 25 of 48
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Reliability of aluminum‐free 808 nm high‐power laser diodes with uncoated mirrors

    Page(s): 3087 - 3089
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    The reliability of uncoated InGaAsP/GaAs high‐power diode lasers emitting at 808 nm wavelength has been studied. 47 W of quasicontinuous wave output power (pulse width 200 μs, frequency 20 Hz) have been obtained from a 1‐cm‐wide laser bar. A single‐stripe diode without mirror coating has been life tested at 40 °C for emitting power of 800 mW continuous wave (cw) and showed no noticeable degradation and no change of the lasing wavelength after 6000 h of operation. © 1995 American Institute of Physics. View full abstract»

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  • Low power electronic optical bistability in single quantum well InP/InGaAsP Fabry–Perot waveguide resonators

    Page(s): 3090 - 3092
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    Optical bistability in a single quantum well waveguide resonator in the InP/InGaAsP material system is demonstrated. High contrast ratio (≳3:1) and switching at low power (≊1.5 mW) was obtained by using a single quantum well at a wavelength near the maximum nonlinear refractive index change and by depositing a reflective coating on the rear end of the waveguide. Clear optical bistability is observed in a wide wavelength range of 1480–1525 nm. Due to the low input power, cw operation of the device was possible at room temperature. © 1995 American Institute of Physics. View full abstract»

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  • Explanation for the temperature insensitivity of the Auger recombination rates in 1.55 μm InP‐based strained‐layer quantum‐well lasers

    Page(s): 3093 - 3095
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    We study the temperature sensitivity of the Auger recombination rates in 1.55 μm InP‐based strained‐layer (SL) quantum‐well (QW) lasers on the basis of the band structures obtained by the self‐consistent numerical solution of the Poisson equation, the scalar effective‐mass equation for the conduction band, and the multiband effective mass equation for the valence band. The results of the theoretical analysis are then compared with the recent experimental results to clarify the basic physical mechanism which determines the Auger recombination rates in SL‐QW lasers. It is shown that the recent temperature sensitivity measurements of Auger recombination coefficients can be consistently explained in terms of the direct band‐to‐band Auger process in the quasi‐two‐dimensional system. We demonstrate that the Auger recombination process in 1.55 μm InP‐based SL‐QW lasers is mainly dominated by the direct band‐to‐band Auger process regardless of QW structures in the temperature range of 273–398 K. © 1995 American Institute of Physics. View full abstract»

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  • Resonant cavity light emitting diode with an AlxOy/GaAs reflector

    Page(s): 3096 - 3098
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    A resonant cavity light emitting diode is fabricated which makes use of a Ag mirror/contact and a buried AlxOy/GaAs Bragg reflector. The buried AlxOy is formed by the selective conversion of AlAs. The differential light output efficiency is measured and found to be ∼5.5% when the AlxOy/GaAs reflector is present versus ∼2.5% for a control device without the AlxOy/GaAs mirror. The measured efficiencies are compared with calculations. © 1995 American Institute of Physics. View full abstract»

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  • Electro‐optic polymer films poled after cross linking

    Page(s): 3099 - 3101
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    The electro‐optic response in a cross‐linked nonlinear optical polymer has been determined as a function of the extent of curing that takes place after coating and drying a film of the material but prior to poling it. It was found that although the value of the electro‐optic coefficient was reduced by partially curing the film before poling, the decrease was minimal even in a fully cured film. Furthermore, the thermal stability of the electro‐optic response was unaffected by the extent of curing before poling. © 1995 American Institute of Physics. View full abstract»

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  • Salient nonlinear optical properties of novel organic crystals comprising π‐conjugated ketones

    Page(s): 3102 - 3104
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    Second‐harmonic generation (SHG) properties of two novel organic crystals, i. e., 2,5‐ bis(benzylidene)cyclopentanone (BBCP) and 2,6‐bis( p‐methylbenzylidene)‐4‐tert‐butylcyclo‐ hexanone (MBBCH), were studied. Based on an x‐ray structural analysis, their SHG coefficients dij at 1.06 μm are determined by the Maker‐fringe method as d14=7 pm/V for BBCP, and d31=15 pm/V, d32=12 pm/V, and d33=4 pm/V for MBBCH, respectively. Measurements on the refractive indices reveal that angle‐tune phase matching in the form of both types I and II is possible, in particular, with a large efficiency for MBBCH, deff∼12 pm/V, which was confirmed experimentally. © 1995 American Institute of Physics. View full abstract»

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  • Fracture strength of free‐standing chemically vapor‐deposited diamond films

    Page(s): 3105 - 3107
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    The fracture strength of free‐standing chemically vapor‐deposited diamond films was assessed by four‐point bending. A two‐parameter Weibull analysis was performed on 130 μm thick films resulting in a Weibull modulus of 4.3 and a statistical scaling stress of 626 MPa. The residual stress in films was measured from the free‐standing film curvature to be 384±10 MPa. The fracture surface chemistry was examined using scanning Auger spectroscopy. The fracture did not occur preferentially along grain boundaries. © 1995 American Institute of Physics. View full abstract»

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  • Evidence for enhanced zinc interstitial concentration in strain‐relaxed heteroepitaxial indium phosphide

    Page(s): 3108 - 3110
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    Heteroepitaxial InP films grown on GaAs substrates by metalorganic chemical vapor deposition are demonstrated to have a higher concentration of zinc occupying interstitial sites than do equivalent homoepitaxial InP layers. A zinc interstitial‐related donor‐to‐acceptor photoluminescence peak is observed in heteroepitaxial InP films which is absent in the homoepitaxial sample spectra. Capacitance–voltage measurements yield a lower hole concentration in the heteroepitaxial layers versus the homoepitaxial layers, which is attributable to a higher fraction of zinc in interstitial sites within the heteroepitaxial layers. Additionally, the hole concentration of the heteroepitaxial layers is found to be lower near the heterojunction as compared with the film surface region, correlating with a higher dislocation density near the heterojunction as seen by transmission electron microscopy. We conclude that the increased zinc interstitial concentration and the reduced hole concentration are due to dislocation‐zinc solute interactions. © 1995 American Institute of Physics. View full abstract»

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  • Hemispherical total emissivity and specific heat capacity of deeply undercooled Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 melts

    Page(s): 3111 - 3113
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    High‐temperature high‐vacuum electrostatic levitation (HTHVESL) and differential scanning calorimetry (DSC) were combined to determine the hemispherical total emissivity ϵT, and the specific heat capacity cp, of the undercooled liquid and throughout the glass transition of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass forming alloy. The ratio of cpT as a function of undercooling was determining from radiative cooling curves measured in the HTHVESL. Using specific heat capacity data obtained by DSC investigations close to the glass transition and above the melting point, ϵT and cp were separated and the specific heat capacity of the whole undercooled liquid region was determined. Furthermore, the hemispherical total emissivity of the liquid was found to be about 0.22 at 980 K. On undercooling the liquid, the emissivity decreases to approximately 0.18 at about 670 K, where the undercooled liquid starts to freeze to a glass. No significant changes of the emissivity are observed as the alloy undergoes the glass transition. © 1995 American Institute of Physics. View full abstract»

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  • Sputter cleaning and smoothening of GaAs(001) using glancing‐angle ion bombardment

    Page(s): 3114 - 3116
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    Flat, clean, essentially defect‐free GaAs(001) surfaces were produced at 570 °C in an As4 overpressure using 1 keV Ar ion bombardment at an impingement angle ϕ of 15° from the surface plane and a dose of 2.3×1016 ions/cm2. Ion bombardment smoothened the surfaces leading to minimum roughness values of ≊0.3 nm and reflection high‐energy electron diffraction (RHEED) patterns that showed streaks with a 2×4 reconstruction. GaAs films grown by molecular beam epitaxy on the sputter cleaned surfaces exhibited strong RHEED oscillations. Cross‐sectional transmission electron microscope images showed that the epitaxial layers and substrates were defect‐free except for 2–3‐nm diam dislocation loops observed 10–20 nm below the substrate surface, separated by ≳100 nm along the interface. © 1995 American Institute of Physics. View full abstract»

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  • Evidence of an energetic ion bombardment mechanism for bias‐enhanced nucleation of diamond

    Page(s): 3117 - 3119
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    The effect of substrate bias voltage was investigated for bias‐enhanced diamond nucleation pretreatments of diamond thin films in a microwave plasma chemical vapor deposition reactor. A critical bias voltage of approximately -200 V was observed for nucleation density enhancement from ∼104 cm-2 to ∼1010 cm-2. Furthermore, the nucleation density under bias conditions was five orders of magnitude lower for a small silicon region electrically isolated from the otherwise negatively biased silicon substrate. These results confirm that bombardment of the substrate by energetic cations plays a significant role in the diamond nucleation mechanism during bias pretreatments. © 1995 American Institute of Physics. View full abstract»

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  • Leakage current behaviors of epitaxial and preferentially oriented Bi4Ti3O12 thin films grown on La0.5Sr0.5CoO3 bottom electrodes

    Page(s): 3120 - 3122
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    Epitaxial and preferentially oriented Bi4Ti3O12 thin films were grown using pulsed laser deposition on LaAlO3(001) and Al2O3(0001) substrates, respectively, with La0.5Sr0.5CoO3 bottom electrode layers. X‐ray diffraction analysis shows that the Bi4Ti3O12 films are grown (001) and (104) oriented on La0.5Sr0.5CoO3(001)/LaAlO3(001) and La0.5Sr0.5CoO3(111)/Al2O3(0001), respectively. These growth behaviors can be explained using arrangements of oxygen ions. Cross‐sectional scanning electron microscopy shows that microstructures of the heterostructures depend on the substrates. It is found that the growth behaviors and the microstructure affect leakage current behaviors of the Bi4Ti3O12 layers. Ohmic and space‐charge‐limited conduction mechanisms are used to explain leakage current behaviors of the Bi4Ti3O12 film on La0.5Sr0.5CoO3/LaAlO3(001) and La0.5Sr0.5CoO3/Al2O3(0001), respectively. © 1995 American Institute of Physics. View full abstract»

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  • Estimation of the configurational entropy of fusion

    Page(s): 3123 - 3125
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    The entropy of fusion of a metal consists of the configurational and vibrational entropies. A formula is presented to evaluate the configurational entropy by assuming an amorphous phase to be a frozen liquid that has lost the configurational entropy but still maintains the vibrational entropy of the corresponding liquid. The magnitude of the configurational entropy may provide information on the nature of liquid structures. The evaluation requires the enthalpy of the amorphous phase in addition to those of the liquid and crystalline phases. The illustrative evaluation on the Ni24Zr76 alloy shows that ΔSconf is approximately 1k per atom, where k is the Boltzmann constant, which suggests some degree of clustering of atoms in the liquid. © 1995 American Institute of Physics. View full abstract»

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  • Fading and self‐irradiation of potassium halide thermoluminescence dosimeters

    Page(s): 3126 - 3127
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    The fading characteristics of KCl:Eu2+ (150 ppm) thermoluminescent crystals is determined. It is shown that the fading cannot be correctly measured without taking into account the phenomenon of self‐irradiation of the crystals, due to natural radioactive nuclide 40K which is presented in potassium halide dosimeters. The results obtained can be useful in those applications of KCl: Eu2+ crystals dealing with long‐time exposures, or low‐dose levels of radiation. © 1995 American Institute of Physics. View full abstract»

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  • Critical influence of reactant pressure on the evolution of single phase CuInSe2 during selenization at low temperatures

    Page(s): 3128 - 3130
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    Single phase chalcopyrite CuInSe2 (CIS) phase formation at low temperatures (≊260 °C) is demonstrated by Se vapor selenization of evaporated metal precursors at a pressure of ≊0.3 mbar. The low pressure changes the relative kinetics of selenization of Cu and In due to the modification of the availability of Se reacting species. Consequently, the thermodynamically favorable reaction CuSe+In(1)+Se→CIS proceeds to completion at lower temperatures. This is confirmed by the absence of In2Se3 at intermediate pressures (0.5–1.0 mbar). At higher pressures (≊7–10 mbar) and Se flux, simultaneous formation of the equilibrium binaries, CuSe and In2Se3 at low temperatures, leads to the formation of CIS through a diffusion limited reaction of the binaries at higher (≥400 °C) temperatures. © 1995 American Institute of Physics. View full abstract»

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  • Formation of diamond during passage of a shock wave in a copper/graphite powder: Formation process and numerical simulation

    Page(s): 3131 - 3133
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    A powder mixture of copper and graphite was dynamically shock‐compressed by a rod‐in‐cylinder method. Structural characterization of the recovered specimen by transmission electron microscopy (TEM) showed the development of fine spherical diamond particles through shock‐induced nuclei formation in the high pressure state and shock‐assisted nuclei growth during unloading to ambient pressure via a solid–liquid–solid (SLS) phase transformation. A 2 μm large diamond particle was formed via a shock‐induced martensitic path. Quantitative numerical simulation applying the two‐dimensional computation code AUTODYN 2D was conducted to evaluate the pressure conditions during shock loading. © 1995 American Institute of Physics. View full abstract»

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  • Thermal conduction normal to diamond‐silicon boundaries

    Page(s): 3134 - 3136
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    Passive diamond layers fabricated using chemical vapor deposition can improve thermal conduction in electronic microstructures. The benefit of using diamond depends strongly on the thermal boundary resistance between active semiconducting regions, where heat is generated, and the diamond. Two independent experimental methods measure the total thermal resistance for conduction normal to 0.2, 0.5, and 2.6 μm thick diamond layers deposited on silicon, providing an upper bound for the effective silicon‐diamond boundary resistance. The data agree with predictions that couple the local phonon scattering rate in the diamond to the grain size. © 1995 American Institute of Physics. View full abstract»

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  • Ballistic electronic stub tuner for potential use in analog‐to‐digital conversion

    Page(s): 3137 - 3139
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    Electron transmission in the fundamental transverse mode of an asymmetric double‐stub electronic stub tuner (ADEST) in the ballistic regime is theoretically shown to be a symmetric, almost sine wavelike, periodic function of an offset parameter d, where d is a measure of the stub asymmetry and is the distance between the lines that bisect the stub and the main wire. The periodic pattern remains quite robust at finite temperatures (≊5 K). This unique multiple folding output characteristic of a single ADEST may conceivably be used for fast, high binary bits analog‐to‐digital conversion. © 1995 American Institute of Physics. View full abstract»

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  • Room‐temperature deep‐blue stimulated emission in ZnS/ZnSe and ZnSTe/ZnSe strained layer superlattices

    Page(s): 3140 - 3142
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    The light emitting properties of ZnS/ZnSe and ZnSTe/ZnSe strained II–VI superlattices are investigated. Room‐temperature stimulated emission by photopumping in the deep‐blue spectral region is observed. An upper limit of threshold carrier density required to achieve lasing is estimated to be 3×1018/cm3.The peak of stimulated emission is several tens of meV red shifted from the spontaneous emission peak, suggesting that exciton‐exciton scattering is involved in the stimulated emission process. © 1995 American Institute of Physics. View full abstract»

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  • Improvement of the electrical properties of metal‐ferroelectric BaMgF4‐silicon capacitor by rapid thermal annealing

    Page(s): 3143 - 3145
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    Use of a rapid thermal annealing technique is shown to improve the electrical properties of metal‐ferroelectric BaMgF4‐silicon capacitors. The fluoride film was deposited in an ultrahigh vacuum system at a substrate temperature of 300 °C. A postdeposition annealing was conducted for 10 s at 600 °C followed by subsequent annealing for 5 s at 750 °C. The results were found out to increase the resistivity of the ferroelectric BaMgF4 film from a typical value of 1–2×1011 Ω cm before the annealing to about 5×1013 Ω cm at 1 MV/cm and reduce the interface state density of the BaMgF4/Si interface to about 8×1010/cm2 eV. Ferroelectric hysteresis measurements using a Sawyer–Tower circuit yielded remanent polarization and coercive field values of about 0.26 μC/cm2 and 315 kV/cm, respectively. © 1995 American Institute of Physics. View full abstract»

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  • Role of mobile hydrogen in the amorphous silicon recrystallization

    Page(s): 3146 - 3148
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    The plasma deposition of nanocrystalline silicon thin films is usually performed under a high flux of atomic hydrogen and hydrogenated chemical species. The growth mechanisms are investigated using the layer‐by‐layer deposition of dense nanocrystalline silicon, obtained at 250 °C by alternating SiH4 and H2 plasmas. In the steady state, a minimum exposure time to the hydrogen plasma is necessary to recrystallize the amorphous top layer (10–85 Å). It is shown that this critical time is determined by the diffusion time of some mobile H through the top a‐Si:H layer. The recrystallization is discussed in relation to the diffusion of hydrogen leading to the nanovoid and broken bond formation processes. © 1995 American Institute of Physics. View full abstract»

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  • Effect of terahertz irradiation on ballistic transport through one‐dimensional quantum point contacts

    Page(s): 3149 - 3151
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    A one‐dimensional ballistic constriction has been fabricated from a two‐dimensional electron gas formed at the interface of a GaAs/AlGaAs heterostructure. The constriction was induced via a pair of front gates which also served as a broadband far‐infrared (FIR) antenna. The photocurrent through the constriction was recorded as a function of source‐drain bias at various FIR frequencies, one‐dimensional subband spacings, and for orthogonal FIR polarizations. The photocurrent was compared to the derivative of dc conductance with respect to source‐drain bias. While dc rectification is shown to dominate the photocurrent, deviations from this model occur at frequencies above ∼1 THz, yielding an estimate of the upper limit of the electron scattering time in the constriction region. © 1995 American Institute of Physics. View full abstract»

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  • Correlation of molecular hydrogen dissociation and the film quality of diamondlike carbon in plasma enhanced chemical vapor deposition

    Page(s): 3152 - 3154
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    The ground state atomic hydrogen density in a hydrogen/acetylene discharge is compared with the diamondlike carbon (DLC) film quality as determined from in situ ellipsometry measurement of the refractive index. Two‐photon laser‐induced fluorescence (LIF) was employed for the detection of the ground state atomic hydrogen in the rf generated discharge. Absolute atomic hydrogen number densities were determined by calibrating the LIF detection system using a transfer standard. A direct correlation was found between the level of molecular hydrogen dissociation in the plasma and the refractive index of the DLC film. © 1995 American Institute of Physics.   View full abstract»

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  • Atomic force microscopy study of ordered GaInP

    Page(s): 3155 - 3157
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    This letter presents an experimental study, using high‐resolution atomic force microscopy, of the nature of the steps on the surface of GaInP layers lattice matched to GaAs substrates. The substrates were intentionally misoriented from the (001) plane by angles of 3°, 6°, and 9° toward [1¯10] and the layers were grown by organometallic vapor phase epitaxy at temperatures of 570, 620, and 720 °C. The surfaces consist of a mixture of monatomic (2.9 Å) [110] steps and [110] oriented supersteps with a distribution of heights from 2 to approximately 17 monolayers. The height of the largest steps increases monotonically with increasing misorientation angle. The supersteps are apparently formed by bunching of monatomic steps producing high index (11n) surfaces (n=4 to 7). This leaves relatively large (several hundred Å) (001) facets adjacent to the supersteps. The superstep height increases and the density decreases with increasing growth temperature. An attempt is made to correlate the supersteps to the degree of order and the microstructure of the ordered domains. © 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