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Applied Physics Letters

Issue 2 • Date Jul 1984

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Displaying Results 1 - 25 of 29
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Fabrication of single mode glass waveguides by electrolytic release of silver ions

    Page(s): 117 - 118
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    We report a novel electrolytic process that is used to fabricate reproducible, low loss, single mode waveguides. By precisely controlling the current pumped through high purity Ag and Pt electrodes in molten NaNO3, as well as its duration, a high degree of accuracy over the release and hence the control of Ag+ concentration is achieved. The inherent capability of the process to generate very low level of silver ion concentration with high precision implies much higher time of diffusion, thus removing the time criticality factor faced by the existing processes while fabricating single mode waveguides. View full abstract»

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  • Reduced chirping in coupled‐cavity‐semiconductor lasers

    Page(s): 119 - 121
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    Chirping in coupled‐cavity lasers is studied experimentally and theoretically. Using a conventional and a cleaved‐coupled‐cavity (C3) laser obtained from the same wafer, we find that the chirp for a C3 laser is typically reduced by a factor of 2. A simple rate equation model is presented to account for reduced chirping. Mode selectivity arising from the cavity coupling is incorporated through wavelength‐dependent cavity‐loss variations. View full abstract»

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  • ‘‘Thermal fixing’’ of Ti‐indiffused LiNbO3 channel waveguides for reduced photorefractive susceptibility

    Page(s): 121 - 123
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    A ‘‘thermal fixing’’ process that dramatically reduces the photorefractive susceptibility of Ti‐indiffused LiNbO3 channel waveguides has been demonstrated. Guided‐wave Mach–Zehnder interferometric modulators were used to characterize the photorefractive susceptibility of the waveguides. These devices were evaluated before and after the thermal fixing process which was seen to be erasable, reproducible, and long‐lived. Photorefractive effects were reduced ten times for waveguide operation at λ=0.46 μm and more than 100 times for operation at λ=0.85 μm. View full abstract»

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  • Self‐sustained picosecond pulse generation in a GaAlAs laser at an electrically tunable repetition rate by optoelectronic feedback

    Page(s): 124 - 126
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    We demonstrate that applying optoelectronic feedback to a high‐speed, self‐pulsing semiconductor laser is an effective and practical means of generating picosecond optical pulses (∼10–20 ps) at a very high repetition rate, between 1 to 5 GHz, which can be electrically tuned. The optical pulses are very stable both on a short term basis with a frequency stability of one part in 105, and on the long term basis as a result of the absence of critical optical alignment. This laser system is potentially very useful in high‐speed electro‐optic signal processing, optical multiplexing, or laser ranging. View full abstract»

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  • Doubly mode‐locked, Q‐switched, continuously pumped neodymium:yttrium aluminum garnet laser

    Page(s): 127 - 129
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    We describe the analysis and operation of an improved actively mode‐locked, Q‐switched continuously pumped neodymium:yttrium aluminum garnet laser. Basically the picosecond laser has been modified by a substitution of the classical output mirror by a convenient Fabry–Perot resonator which is used as the reflective element in order to provide an efficient reshaping of the picopulses. Instead of providing transform limited pulses with 100‐ps duration at 1‐MW peak power, our system is able to deliver sharper picopulses (18 ps) without significant loss in the overall efficiency. Besides obvious basic research applications, this low cost, easy to do modification may turn out to be extremely useful whenever laser implants and material cutting are concerned. View full abstract»

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  • Important role of dynamical atomic processes on x‐ray line emissions from picosecond laser‐produced plasmas in the ionizing phase

    Page(s): 130 - 132
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    Transient characteristics of x‐ray line radiation from high density plasmas in an ionizing phase are computationally shown in the picosecond region by solving coupled rate equations. Many atomic processes associated with x‐ray radiation are found to affect temporal changes of x‐ray intensities and, especially, the x‐ray intensity ratios. It is pointed out that in the evaluation of electron temperatures in transient plasmas, undesirable errors are apt to be brought about by usual conventional methods based on computations in which steady state equilibrium is assumed. View full abstract»

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  • Plasma etching in magnetic multipole microwave discharge

    Page(s): 132 - 134
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    A plasma etching reactor is described which associates surface magnetic confinement, microwave discharge, and independently controlled substrate biasing. Preliminary measurements show that the reactor produces reactive plasmas allowing anisotropic fine line etching at low ion energy. View full abstract»

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  • Initial transient phenomena in the plasma enhanced chemical vapor deposition process

    Page(s): 134 - 136
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    A strong correlation between a silicon‐rich interface in plasma deposited silicon nitride films with an initial transient phenomena during the plasma enhanced chemical vapor deposition process has been verified using optical emission techniques, plasma voltage potential (Vp) measurements, and Auger depth profile analysis. The data suggested that the silicon‐rich interface may be an intrinsic property of all plasma deposited films examined. This observation was found to be independent of tool type. However, it is possible to reduce the silicon‐rich interface thickness in plasma deposited films by shortening the transient time with judicious choice of tool and deposition conditions. View full abstract»

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  • Enhancement of thin metallic film adhesion following vacuum ultraviolet irradiation

    Page(s): 137 - 139
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    The adhesion of thin metallic films to silicon substrates is shown to improve following irradiation with a flux of either 21.2‐eV (He I) 10.2‐eV (H Lyman α) photons. The improved adhesion is similar to that found following MeV energy ion irradiation and keV energy electron irradiation, adding support to the view that electronic excitation and/or ionization and precursors to the stronger bonding configuration. View full abstract»

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  • Effects of impurities on the oxidation of MoSi2 on silicon

    Page(s): 140 - 142
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    When MoSi2 films on silicon are exposed to oxidizing ambients, a continuous layer of SiO2 grows on the silicide surface. However, when the presence of oxygen impurities exceeds 2 at. % at the silicon‐MoSi2 interface, metal‐rich silicide phases form. The coexistence of these phases and the absence of metal oxides are explained by considering both the oxidation kinetics and the ternary phase diagram of the Mo‐Si‐O system. View full abstract»

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  • Oxygen gettering by hafnium implanted in beryllium: A 〈0001〉 Hf‐O dumbbell?

    Page(s): 143 - 145
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    The interaction of hafnium implanted into beryllium single crystals with diffusing oxygen was studied using hyperfine interaction and Rutherford backscattering channeling techniques. It was observed that oxygen is trapped at hafnium in a well defined lattice position. The formation of a 〈0001〉 Hf‐O mixed dumbbell in the tetrahedral interstitial cage of the beryllium lattice is suggested to explain the experimental results. View full abstract»

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  • Polycrystalline CdS photocorrosion studied by capacitance and action spectra measurements

    Page(s): 146 - 147
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    Polychromatic illumination of polycrystalline CdS films in contact with basic aqueous solutions of 1 M cysteine increases the photocurrent as a function of time. It is shown that the evolution of the photocurrent spectra and Mott–Schottky plots, recorded as a function of the illumination time, is in agreement with the formation of a mixed film CdS1-xOx at the surface, leading eventually to an amorphous CdO layer. View full abstract»

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  • 12% solar conversion efficiency by interphase restructuring

    Page(s): 148 - 149
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    Solar energy conversion efficiency of n‐CuInSe2/p‐CuISe3 heterojunction formed in situ and contacted by I-‐I2‐Cu+‐HI electrolyte has been increased to 12% by modifying the growth conditions of the p‐CuISe3 phase. These include the use of prepolished n‐CuInSe2 (110) surfaces, higher concentrations of HI and Cu+, and an air anneal at 200 °C. X‐ray fluorescence analysis in conjunction with scanning electron micrographs of the new interphase indicates structural and compositional alterations and possibly further transformation of CuISe3 to CuIn2Se3I. Temperature dependence of the cell performance indicates solid state effects and relative independence of electrochemical kinetics. View full abstract»

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  • Photoluminescent and electroluminescent properties of GaAs1-xPx‐GaAs1-yPy isotype heterojunction electrodes

    Page(s): 150 - 152
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    The photoluminescence (PL) of N‐n GaAs0.59P0.41‐GaAs0.70P0.30 heterojunction electrodes has been studied in stable, efficient photoelectrochemical cells employing aqueous ditelluride electrolyte. When excited at several ultra‐band‐gap wavelengths, electrodes whose surface n‐GaAs0.70P0.30 layers are ∼0.2 μm thick exhibit PL spectra derived from the emission bands of the heterojunction constituents. Besides being dependent on excitation wavelength, the PL spectral distribution is a function of applied potential. Field‐induced quenching of PL from the electrodes is shown to be consistent with a dead‐layer model. Electroluminescence (EL) can be observed when the solids are used as cathodes in a formamide solution of Na2S2O8. The EL spectrum indicates that radiative recombination due to hole injection is largely confined to the surface layer. View full abstract»

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  • Molecular beam epitaxial growth of InGaP/InAlP quantum well structures for the visible wavelength region

    Page(s): 152 - 154
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    InGaP InAlP quantum well structures for the visible wavelength region have been grown by molecular beam epitaxy for the first time. The formation of the superlattice structure was confirmed for the multiquantum well structure wafer by double crystal x‐ray diffraction measurement and sputtering Auger electron measurement. Photoluminescence measurement at 77 K on the multilayer structure wafer with different thickness InGaP well layers showed that quantum levels were formed in InGaP well layers. View full abstract»

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  • Direct electron beam writing of gallium oxide on GaAs(111) As surfaces

    Page(s): 154 - 156
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    In this letter we show the possibility of a direct electron beam writing on GaAs (111) As by electron stimulated oxidation. An estimate of the writing velocity is also given. The analysis of the profiles of the oxide spots by Auger spectroscopy indicates the stability of the gallium oxide formed, and the post‐oxidation formation of an As‐rich interface. View full abstract»

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  • Effect of chlorine implantation on oxidation enhanced diffusion of phosphorus in silicon

    Page(s): 157 - 159
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    It is shown that chlorine implantation in silicon reduces the phosphorus enhanced diffusivity in oxidizing atmosphere (both dry O2 and steam) at 1000 and 1100 °C. On the contrary, no change has been evidenced on the diffusivity in inert ambient. Cl implantation is shown to be effective also in avoiding the formation of oxidation induced stacking faults. These effects can be explained hypothesizing a direct interaction between chlorine atoms and silicon self‐interstitials, which reduces the interstitial excess produced by oxidation. Furthermore, it has been observed that the presence of chlorine in silicon enhances the oxidation rate both in dry O2 and in steam atmospheres. View full abstract»

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  • Thermal radiation from laser heated silicon and pyrometric temperature measurements

    Page(s): 159 - 161
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    We report time‐resolved measurements of thermal radiation during laser heating of silicon using 10‐ns laser pulses. The data provide further evidence that the laser‐induced high reflectivity phase is due to melting of the surface. From thermal emission spectra the evolution of the surface temperature for both the crystalline and the liquid state is obtained. View full abstract»

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  • Graded band‐gap p/n AlGaAs solar cells grown by organometallic vapor phase epitaxy

    Page(s): 162 - 164
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    The growth of p/n graded band‐gap AlGaAs/GaAs solar cells by organometallic vapor phase epitaxy is reported. The best performance is obtained for a cell with the emitter graded from 0 to 45 at. % aluminum over a distance of 0.3 μm. The corresponding solar cell parameters are Isc=27.3 mA/cm2, Voc=1.01 V, and FF=0.73 at 1 sun AM0, corresponding to a conversion efficiency of 14.7%. View full abstract»

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  • Anomalous photomagnetoresistance effect in modulation‐doped AlGaAs/GaAs heterostructures

    Page(s): 164 - 167
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    A novel negative photoresistance effect at Al0.3Ga0.7As/GaAs interface in the presence of a magnetic field B is discovered and explained. At low temperatures (T=4.2 K) illumination of the sample leads to a persistent electron accumulation in the GaAs channel (the well‐known persistent photoconductivity effect). In the presence of B≳0.3 T the dependence of the longitudinal resistance (as measured by the four‐probe method) shows an anomalous behavior in that the resistance increases sharply with the increasing concentration n of carriers provided by light. In the same range of concentrations the longitudinal resistance at fixed n is proportional to B2. It is shown that the observed behavior of the resistance is associated with photoexcitation of electrons from donor vacancy (DX) centers in the highly doped AlGaAs region resulting in the creation of a second conducting layer of high charge density and low mobility. View full abstract»

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  • Infrared excitation spectrum of 40.4‐meV acceptor level in neutron‐irradiated gallium‐doped silicon

    Page(s): 167 - 168
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    An infrared absorption spectrum has been obtained for the shallow A2 acceptor level formed by neutron irradiation of Si:Ga. After a 600 °C anneal, absorption peaks were observed at 213.1, 244.9, and 286.9 cm.-1 These peaks appear to correspond to lines 1, 2, and 4 of a group III‐like acceptor spectrum originating from a ground state with a 40.4‐meV binding energy. Hall effect measurements confirm the presence of an acceptor level at this energy. View full abstract»

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  • Titanium disilicide formation by wide‐area electron beam irradiation

    Page(s): 169 - 171
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    We describe the use of a wide‐area (38 cm2) electron beam as a heat source to interdiffuse 400‐Å‐thick sputter‐deposited titanium films into 3–6‐Ω cm〈100〉 n‐type silicon wafers. Isochronal exposures of 30 s with electron beam of current densities greater than 250 mA/cm2 reduced the as‐deposited sheet resistance by a factor of 10, while exposures at half this current caused the sheet resistance to increase by a factor of 2.5. Compositional depth profiles obtained from a combination of ion beam sputtering and Auger electron spectroscopy show that this resistivity increase is caused by diffusion of oxygen into the titanium film induced by the electron beam heating. At exposures to beam intensities sufficient to induce complete silicide formation, oxygen is segregated at the surface by the advancing silicon. We conclude that the silicide self‐cleanses itself of oxygen during formation. View full abstract»

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  • Characteristics of amorphous silicon staggered‐electrode thin‐film transistors

    Page(s): 171 - 173
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    Amorphous silicon staggered‐electrode thin‐film transistors (TFT’s) can show current crowding near the origin in the output characteristics. The degree of current crowding is governed by the voltage dependence of the current flowing from the n+ contact to the conducting channel. This current is a space‐charge‐limited current whose magnitude depends on the bulk density of states in the undoped intrinsic layer. For a 0.5‐μm‐thick i layer, calculations predict negligible current crowding for N(E)≪1016 cm-3 eV-1, but severe current crowding for N(E)≫3×1016 cm-3 eV-1. Experimental results are consistent with N(E) in the range 1016 cm-3 eV-1–2×1016 cm-3 eV-1. This is lower than the value derived from the transfer characteristic of the TFT (∼1017 cm-3 eV-1), which is evidence for an inhomogeneous distribution of deep gap states through the 0.5‐μm film of α‐Si:H. View full abstract»

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  • Synchrotron photoemission investigation: Fluorine on silicon surfaces

    Page(s): 174 - 176
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    High resolution core level photoemission spectroscopy has been used to obtain the first direct identification of the chemical species remaining on silicon surfaces after exposure to fluorine. Both Si(111) 2×1 and Si(111) 7×7 were exposed to fluorine via the dissociative chemisorption of XeF2. For fluorine coverages in the monolayer regime, SiF1, SiF2, and SiF3 were all present although their relative abundance varied significantly between the two surfaces. No evidence for the existence of unreacted interestitial fluorine was found. These results suggest the need for modification of current models describing plasma and reactive ion etching of silicon. 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