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Applied Physics Letters

Issue 14 • Date Oct 1992

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Displaying Results 1 - 25 of 44
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • 1×16 photonic switch operating at 1.55 μm wavelength based on optical amplifiers and a passive optical splitter

    Page(s): 1613 - 1615
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    An InP based 1×16 optical switch is demonstrated. The sixteen output ports are spaced 250 μm apart, and the total device length is 5.9 mm. Optical amplifiers are used to gate the optical signals and to provide optical gain. The total loss of the device, excluding coupling, is less than 2.5 dB and loss free operation was observed at low input powers. The output extinction ratios are lower than 18 dB and the uniformity spread of the sixteen channels is as low as 6.7 dB. View full abstract»

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  • Optical second harmonic generation in Langmuir–Blodgett films of n‐docosyl‐2‐methyl‐4‐nitroaniline

    Page(s): 1616 - 1618
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    The preparation of Langmuir–Blodgett (LB) films of n‐docosyl‐2‐methyl‐4‐nitroaniline (DCMNA) is reported. LB multilayers of DCMNA are highly anisotropic showing a strong absorption for light polarized parallel to the dipping direction. Furthermore, optical second harmonic generation was observed from LB multilayers of DCMNA. The SH signal was always polarized parallel to the dipping direction; and maximum SH intensity was obtained when the direction of the fundamental wave was also polarized parallel to this direction. The SH intensity increased quadratically with the number of LB layers up to 50 layers. Preliminary x‐ray diffraction studies indicate a Y‐type arrangement for the molecules with a bilayer spacing of 3.77 nm and a strong tilt angle of 34° for the alkyl chains with respect to the substrate plane. View full abstract»

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  • Versatile waveguide polarizer incorporating an ultrathin discontinuous silver film

    Page(s): 1619 - 1621
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    We demonstrate the first transverse magnetic (TM) pass waveguide polarizer suitable for integrated optic or fiber optic geometries. The polarizing properties of waveguides incorporating an ultrathin discontinuous silver film are due to excitation of a localized surface plasmon mode. The polarizers have a large bandwidth (≳100 nm), high extinction ratios, and do not rely on sensitive phase matching conditions. We illustrate these novel polarizing properties on ion‐exchanged planar waveguides overlayed with a 5‐nm‐mass thick silver film. The measured extinction ratio was 35 dB/mm at 836 nm with 2 dB/mm loss for the TM polarization. The theoretical analysis of the film properties and waveguide propagation losses is compared with the experiments. View full abstract»

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  • Low‐loss metallic hollow waveguides coated with durable and nontoxic ZnS

    Page(s): 1622 - 1623
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    ZnS‐coated Ag hollow waveguides are newly proposed and fabricated to realize a durable and nontoxic waveguide for CO2 laser light transmission. The fabrication method is based on rf‐sputtering and electroplating techniques and a polyimide tube is used as a hollow mandrel. As a result of measurements, low‐loss property of the ZnS‐coated waveguide is shown and the beam profile with a sharp energy peak is obtained. The result of the aging test proves good durability of the ZnS‐coated Ag waveguide. View full abstract»

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  • CO2 laser power transmission and laser induced breakdown in AgClxBr1-x crystals, polycrystals, and fibers

    Page(s): 1624 - 1625
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    Laser‐induced breakdown (LIB) thresholds in AgClxBr1-x crystals, polycrystals, and fibers were studied under CO2 pulse laser excitation. The limit value of LIB threshold Pc of the bulk crystals is about 4×108 W/cm2 for x=1 and 8×108 W/cm2 for x=0 under 100 ns transversely excited atmospheric pressure laser excitation. The LIB threshold in fibers is much smaller; about 2×107 W/cm2. The dependence of the LIB on composition and temperature suggests that the main cause for LIB is electron avalanche combined with multiphonon absorption at 10.6 μm in silver halide crystals. View full abstract»

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  • Re‐evaluation of the thermal stability of optically nonlinear polymeric guest‐host systems

    Page(s): 1626 - 1628
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    Guest‐host polymer systems with potential use in electro‐optic devices are discussed. The polymer host is a polyimide and the guest chromophores are 2,4,5‐triarylimidazoles (lophines). Poling stabilities have been obtained by extrapolating the second harmonic generation decay using a stretched exponential function and extrapolated lifetimes greater than a year at 80 °C have been obtained. In addition, an apparent relationship between the stability of poled order and the glass transition temperature is discussed. View full abstract»

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  • Synthesis of diamond/β‐SiC composite films by microwave plasma assisted chemical vapor deposition

    Page(s): 1629 - 1631
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    A new kind of microcrystalline composite films consisting of diamond and cubic silicon carbide (β‐SiC) has been synthesized in a microwave plasma assisted chemical vapor deposition process (MWCVD), using a gas mixture of hydrogen, methane, and tetramethylsilane. Single crystalline (111) silicon wafers and polycrystalline tungsten carbide, which were treated with diamond paste before the deposition, were used as substrates. Scanning electron microscopy, electron probe microanalysis, infrared absorption, Raman scattering, and x‐ray diffraction analysis were performed to characterize the film quality and the crystallographic structure. The results show that the film structure and the volume fractions of diamond and β‐SiC components depend mainly on the reactive gas concentrations and on the diamond nucleation density. By adjusting the reactive gas concentration, the volume fraction of the components can be varied over the film thickness. In addition, the growth texture of the diamond phases can be influenced by the β‐SiC phase orientation. View full abstract»

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  • Oriented nickel‐titanium shape memory alloy films prepared by annealing during deposition

    Page(s): 1632 - 1634
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    Nickel‐titanium shape memory alloy films, between 2 and 10 μm thick, were sputter deposited onto (100) silicon substrates. Films deposited onto a substrate at ambient temperature were amorphous; however, several post‐deposition annealing procedures produced crystalline films exhibiting the B2‐to‐B19’ phase transition that gives rise to the shape memory effect. Films that were deposited onto a heated substrate, 350–460 °C, crystallized during deposition, eliminating the need for a separate annealing step. Powder x‐ray diffraction indicated that these films were highly oriented, with the NiTi (110)B2 face parallel to the silicon substrate (100) face. View full abstract»

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  • X‐ray damage in low temperature ultrathin silicon dioxide

    Page(s): 1635 - 1637
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    The electrical characteristics of ultrathin oxides used in an x‐ray lithography n‐channel metal‐oxide‐silicon process grown at 700 and 950 °C were studied. The breakdown field exceeded 15 MV/cm for both low and high temperature oxides and the interface trap density of the fresh oxide was of order of 1010 cm-2 eV-1. Oxides grown at 950 °C had a lower interface trap density than 700 °C oxides, but 950 °C oxides are more sensitive to x‐ray radiation damage. After 350 °C hydrogen annealing about 80% of the radiation damage in the form of interface traps was recovered. View full abstract»

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  • On the mechanism of dimensional change of neutron irradiated graphite

    Page(s): 1638 - 1640
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    In order to investigate the mechanism of large volume expansion of graphite due to neutron irradiation we have made in situ observation of damage structure of graphite with a high resolution transmission electron microscope (HRTEM). Both bending and randomizing the orientation of broken basal planes are proposed to be the origin for the large volume expansion of the irradiated graphite. It is also found that graphite easily loses its lattice ordering in the basal planes as demonstrated by halo rings in the (101¯0) diffraction pattern, while hardly losing its layered structure, i.e., (002) spots are retained. View full abstract»

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  • Thermo‐electro‐optic switch based on polymer dispersed liquid crystal composite

    Page(s): 1641 - 1642
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    A new type of thermo‐electro‐optic switch based on polymer dispersed liquid crystal (PDLC) composite is reported below. The PDLC composite has been made by dispersing a dual frequency addressable liquid crystal (LC) mixture in an isotropic polymer matrix in the form of very fine droplets of micron and submicron sizes. The PDLC cell in the presence of an electric field can be made to switch from transparent to scattering state or vice‐versa by varying its temperature by ±≥1 °C, respectively. Moreover, the transition temperature of the PDLC switch can be set by varying the frequency of the electric biasing field. View full abstract»

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  • Growth of epitaxial Pb(Zr,Ti)O3 films by pulsed laser deposition

    Page(s): 1643 - 1645
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    Lead zirconate titanate (PZT) thin films with a composition near the morphotropic phase boundary have been grown on MgO (100) and Y1Ba2Cu3Ox (YBCO) coated MgO substrates. Substrate temperature and oxygen pressure were varied to achieve ferroelectric films with a perovskite structure. Films grown on MgO had the perovskite structure with an epitaxial relationship with the MgO substrate. On the other hand, films grown on the YBCO/MgO substrate had an oriented structure to the surface normal with a misorientation in the plane parallel to the surface. The measured dielectric constant and loss tangent at 1 kHz were 670 and 0.05, respectively. The remnant polarization and coercive field were 42 μC/cm2 and 53 kV/cm. A large internal bias field (12 kV/cm) was observed in the as‐deposited state of the undoped PZT films. View full abstract»

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  • Low‐temperature growth of high resistivity GaP by gas‐source molecular beam epitaxy

    Page(s): 1646 - 1648
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    GaP films were epitaxially grown on GaP substrates at a low temperature ∼200 °C using gas source molecular beam epitaxy (MBE). The lattice constant of these LT GaP films was found to be larger than that of both the GaP substrate and films grown at high temperatures. These results can be explained by excess phosphorus present in these LT films. The resistivity of these films is comparable to that of the semi‐insulating (SI) GaP substrate. These results are considered the first demonstration of high resistivity, semi‐insulating LT GaP films. View full abstract»

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  • Photoinduced hydrogen loss from porous silicon

    Page(s): 1649 - 1651
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    In this letter we show that UV illumination of porous silicon causes a decrease in its luminescence efficiency. Infrared measurements allow us to associate the efficiency decrease with a loss of hydrogen from the silicon surface. We also find that the rate at which the luminescence intensity degrades increases rapidly when the illumination energy exceeds a threshold near 3.0 eV. We conclude that the decrease in photoluminescence efficiency occurs as a result of optically induced hydrogen desorption and discuss possible explanations for the energy threshold.   View full abstract»

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  • Observation of magnetic focusing in two‐dimensional hole systems

    Page(s): 1652 - 1654
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    We report the first observation of transverse magnetic hole focusing in high quality two‐dimensional hole systems confined in square and triangular quantum wells grown on (311)A GaAs substrates. The results demonstrate ballistic hole transport over distances up to 11 μm and allow us to probe the constant energy contours in k‐space for these two types of confinement. View full abstract»

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  • Photoemission study of porous silicon

    Page(s): 1655 - 1657
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    We report x‐ray photoelectron spectra from a porous silicon film (PSF) with a photoluminescence peak at 1.8 eV, as a function of argon ion etching time to probe the composition in the surface and the subsurface regions. The results clearly indicate that the surface layer is essentially a fluorine admixed SiO2 phase, while the Si:O:F composition of the subsurface region 2:1:0.2. With the possibility of the existence of hydrogen in this composition it appears that beyond the highly oxidized surface, PSF is a fluorine substituted siloxene derivative, which can be responsible for the visible photoluminescence. View full abstract»

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  • Molecular‐beam‐epitaxial growth of n‐AlGaAs on clean Cl2‐gas etched GaAs surfaces and the formation of high mobility two‐dimensional electron gas at the etch‐regrown interfaces

    Page(s): 1658 - 1660
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    By using an ultrahigh vacuum multichamber process system, very clean GaAs surface is successfully prepared by chlorine‐gas etching and AlGaAs is subsequently grown by molecular beam epitaxy to show that two‐dimensional electron gas is successfully formed at etch‐regrown AlGaAs/GaAs interface. Mobility as high as 114 000 cm2/V s at 9.8 K is achieved for the carrier concentration NS=4.5×1011 cm-2. From the secondary‐ion‐mass‐spectroscopy measurement, the carbon concentration at the interface is estimated to be 2×1010 cm-2, and is found to be a dominant scatterer for the two‐dimensional electrons. A transmission‐electron‐microscope image has evidenced a very flat feature of etch‐regrown interface. View full abstract»

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  • Optical gain and ultrafast nonlinear response in GaAs/AlAs type‐II quantum wells

    Page(s): 1661 - 1663
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    We describe the femtosecond optical gain nonlinearities for the unusual case of electrons which are distributed between the direct‐GaAs and indirect‐AlAs layers in a GaAs/AlAs type‐II multiple quantum‐well (MQW) structure. Due to the spatial separation of electrons from the holes, we observe a significant increase in the gain lifetime (≳150 ps) in type‐II MQWs, as compared to type ‐I MQWs (∼50 ps). In addition, we investigate the effect of a longitudinal electric field on Γ‐X energy splitting in type‐II structures. Finally, at early times we observe an ultrafast nonlinear optical response in the gain/absorption spectra which we attributed to electron‐hole scattering without carrier loss.   View full abstract»

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  • Enhanced electro‐optic effect in amorphous hydrogenated silicon based waveguides

    Page(s): 1664 - 1666
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    We report on a direct measurement of the electro‐optic effect in amorphous hydrogenated silicon based waveguides. The observed phase modulation with an applied voltage shows evidence of a threshold voltage below which the electro‐optic effect is weak. At high voltages the electro‐optic phase modulation is nonquadratic and significantly enhanced with respect to the bulk effect in amorphous silicon. These results are explained in terms of a model which considers inhomogeneous electric fields within the silicon layer due to voltage dependent space charges. View full abstract»

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  • n‐ and p‐type in‐plane gated field effect transistors directly written on a semi‐insulating GaAs substrate

    Page(s): 1667 - 1669
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    A new type in‐plane gated field effect transistor where the semi‐insulating substrate itself is used as a gate insulator region is proposed. n‐ and p‐type in‐plane gated field effect transistors are fabricated on a semi‐insulating GaAs substrate by focused ion beam scanning of Si++ and Be++, respectively. These in‐plane gated field effect transistors are found to operate well at room temperature.   View full abstract»

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  • Hydrogen diffusion in polycrystalline silicon thin films

    Page(s): 1670 - 1672
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    Grain boundaries in undoped polycrystalline silicon (poly‐Si) thin films are shown to act as efficient hydrogen traps rather than as paths of enhanced diffusion. A comparison of hydrogen diffusion in poly‐Si and undoped single‐crystal silicon (c‐Si) demonstrates that the diffusion in poly‐Si is significantly suppressed compared to c‐Si. These results have significant implications for hydrogenation of poly‐Si thin‐film transistors. View full abstract»

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  • In0.53Ga0.47As p‐i‐n photodiodes with transparent cadmium tin oxide contacts

    Page(s): 1673 - 1675
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    A new type of p‐i‐n In0.53Ga0.47As photodiode having an optically transparent composite top electrode consisting of a thin semitransparent metal layer and a transparent cadmium tin oxide (CTO) layer was investigated. The composite functions as the n or p contact, an optical window, and an antireflection coating. The transparent contact also prevents shadowing of the active layer by the top electrode, thus allowing greater collection of incident light. Since the CTO contact is nonalloyed, interdiffusion into the i‐region is not relevant avoiding an increased dark current. The photodiodes exhibited leakage currents of ≤8 nA and some as low as 23 pA, with reverse breakdown voltages of ≥15–17 V. Responsivity was measured using a 1.55 μm InGaAsP diode laser focused onto an unpassivated 60 μm diam p‐i‐n photodiode and was ≥0.41 A/W. Photoresponse of the diodes to 3 ps pulses from a Nd:YLF laser (λ=1.047 μm) was 169 and 86 ps for the 60 and 9 μm diodes, respectively. The maximum frequency response of the 9 μm diode is packaging limited, and is expected to have an intrinsic response time of 20–30 ps. View full abstract»

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  • Arsenic doping of GeSi epitaxial layers grown in the dichlorosilane/germane system

    Page(s): 1676 - 1678
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    In this letter we detail the effects of arsine on Ge1-xSix growth rate and doping. We have observed for the first time that the growth process is no longer well described by a simple first‐order reaction. The growth‐rate data instead are consistent with a second‐order reaction, with a substantial change in the activation energy. The electron carrier concentration and mobility have been measured as functions of arsine flow and compared to similar data from silicon growth. View full abstract»

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  • Defects in low‐temperature‐grown GaAs annealed at 800 °C

    Page(s): 1679 - 1681
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    GaAs grown by molecular beam epitaxy (MBE) at 300 °C is annealed at 800 °C and optical properties are studied using photoluminescence spectroscopy (PL) and infrared‐absorption spectroscopy. Three kinds of defects are observed. One of them is attributed to gallium vacancies with an energy level at 0.3 eV above the valence‐band edge. The concentration of gallium vacancies is increased by the high‐temperature annealing. The GaAs can render inactive free electrons of 1.3×1018 cm-3 even after annealing at 800 °C for 10 min. 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