By Topic

Applied Physics Letters

Issue 19 • Date May 2004

Filter Results

Displaying Results 1 - 25 of 75
  • Issue Cover

    Page(s): c1
    Save to Project icon | PDF file iconPDF (400 KB)  
    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
    Save to Project icon | PDF file iconPDF (40 KB)  
    Freely Available from IEEE
  • Influence of vapors of volatile organic compounds on spectral shift of bending vibrations of freely suspended ferroelectric liquid-crystal films

    Page(s): 3723 - 3725
    Save to Project icon | PDF file iconPDF (64 KB)  

    The influence of the vapors of volatile inert fluorocarbon compounds on the mechanical properties of freely suspended ferroelectric liquid-crystal films has been studied. It was shown that spectral shift of bending vibrations of freely suspended films depends on the mass variations of the associated ambient gas as well as on the adsorption of the vapors of volatile fluorocarbon compounds onto the film surface. It was also shown that adsorption layers similar to surfactants decrease the film surface tension by 11%–35% (4–12.5 dyn/cm). © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Field-effect transistor based on KTaO3 perovskite

    Page(s): 3726 - 3728
    Save to Project icon | PDF file iconPDF (126 KB)  

    An n-channel accumulation-type field-effect transistor (FET) has been fabricated utilizing a KTaO3 single crystal as an active element and a sputtered amorphous Al2O3 film as a gate insulator. The device demonstrated an ON/OFF ratio of 104 and a field-effect mobility of 0.4 cm2/V s at room temperature, both of which are much better than those of the SrTiO3 FETs reported previously. The field-effect mobility was almost temperature independent down to 200 K. Our results indicate that the Al2O3/KTaO3 interface is worthy of further investigations as an alternative system of future oxide electronics. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Fabrication of crystalline organic waveguides with an exceptionally large electro-optic coefficient

    Page(s): 3729 - 3731
    Save to Project icon | PDF file iconPDF (311 KB)  

    Single-crystal optical waveguides of 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST), an organic material with a large electro-optic coefficient, have been obtained. DAST decomposes at its melting temperature, making its growth from the melt difficult. However, graphoepitaxy allows for ≫1 mm s-1 growth, 1×105 times faster than conventional techniques, and produces crystals of the correct dimensions for optical waveguides, 1–15 μm on a side and 5–10 mm long. The crystals grow with the c-axis normal to the substrate, and with in-plane orientation determined by lithographic patterning. The electro-optic coefficient dn/dE is 600±300 pm V-1 at 1.55 μm wavelength. Optical losses are ≪10 dB cm-1. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Highly resistive p-PbTe films with carrier concentration as low as 1014 cm-3

    Page(s): 3732 - 3734
    Save to Project icon | PDF file iconPDF (250 KB)  

    We propose here a model according to which a high density of semiconductor–insulator interface states can deplete practically the whole film volume, provided that the film thickness is of the order of Debye screening length. We demonstrated this experimentally by showing that thin p-PbTe films, thermally deposited on mica substrate, have an unusually low concentration of free holes, as low as 1014 cm-3 at 100 K, resulting in a very high value of resistance, Hall constant, and Seebeck coefficient, respectively. Such low concentration of free carriers allows an investigation of a whole series of phenomena in AIVBVI semiconductors, such as injection currents, injection electroluminescence, electronic memory phenomena, electric field effect control of thermopower, and more. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Radiative efficiency limits of solar cells with lateral band-gap fluctuations

    Page(s): 3735 - 3737
    Save to Project icon | PDF file iconPDF (63 KB)  

    The radiative recombination limit of photovoltaic power conversion under one sun terrestrial illumination is calculated for solar cells with lateral fluctuations of the band-gap energy. A simple analytical model quantifies the fluctuations by the standard deviation σEg from the mean band gap. The calculated maximum efficiency decreases by 1.7% (absolute) for σEg=50 meV and by 6.1% for σEg=100 meV with respect to a uniform band gap. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Liquid-phase fabrication of patterned carbon nanotube field emission cathodes

    Page(s): 3738 - 3740
    Save to Project icon | PDF file iconPDF (243 KB)  

    High-resolution electron field emission cathodes were fabricated at room temperature by a high throughput electrophoresis process using functionalized carbon nanotubes (CNTs). Well-defined and adherent CNT patterns with 20 μm feature size were achieved on a variety of substrates with fine control of the CNT morphology. The cathodes show uniform emission pattern across the entire surfaces and emission current with long-term stability. This room-temperature liquid-phase process is efficient and has no intrinsic limit on the deposition area. The emission characteristics of these cathodes compare favorably to those from other fabrication methods for CNT based field emission display applications. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Effect of surface NH3 anneal on the physical and electrical properties of HfO2 films on Ge substrate

    Page(s): 3741 - 3743
    Save to Project icon | PDF file iconPDF (159 KB)  

    Metal-oxide-semiconductor capacitors were fabricated on germanium substrates by using metalorganic-chemical-vapor-deposited HfO2 as the dielectric and TaN as the metal gate electrode. It is demonstrated that a surface annealing step in NH3 ambient before the HfO2 deposition could result in significant improvement in both gate leakage current and the equivalent oxide thickness (EOT). It was possible to achieve a capacitor with an EOT of 10.5 Å and a leakage current of 5.02×10-5A/cm2 at 1 V gate bias. X-ray photoelectron spectroscopy analysis indicates the formation of GeON during surface NH3 anneal. The presence of Ge was also detected within the HfO2 films. This may be due to Ge diffusion at the high temperature (∼400 °C) used in the chemical-vapor deposition process. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Toward improved and tunable polymer field-effect transistors

    Page(s): 3744 - 3746
    Save to Project icon | PDF file iconPDF (102 KB)  

    We report an electrochemical method to improve charge injection in thin-film field-effect transistors fabricated with semiconducting polymers. By having ions, which are mobile only at elevated temperatures, in the active material [a mixture of a soluble poly(para-phenylene vinylene) copolymer, a crown ether and a LiCF3SO3 salt] we create electric double layers at the drain/source Au electrode interfaces by applying a low voltage (V=2 V) at T=85 °C for a short time (t∼1–5 min). After cooling to room temperature under applied voltage, we demonstrate significantly improved transistor performance. In addition, we present evidence of reversible electrochemical doping in this active material. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Imaging phonons in a fcc Pu–Ga alloy by thermal diffuse x-ray scattering

    Page(s): 3747 - 3749
    Save to Project icon | PDF file iconPDF (290 KB)  

    X-ray thermal diffuse scattering intensity patterns from phonons in a fcc δ-Pu–Ga alloy have been recorded using an 18 keV undulator x-ray beam with a beam diameter of 25 μm. The results are consistent with patterns calculated using the Born–von Karman force constant model of lattice dynamics, and support the pronounced softening of the transverse acoustic branch along the [111] direction observed from inelastic x-ray scattering measurements. This work demonstrates the feasibility of using a “large-grain, small beam” approach to study lattice properties, such as phonon dispersion curves, of materials not readily available in the form of large single crystals. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Hybrid near-field scanning optical microscopy tips for live cell measurements

    Page(s): 3750 - 3752
    Save to Project icon | PDF file iconPDF (370 KB)  

    We report a near-field scanning optical microscopy (NSOM) probe that enables high-resolution imaging of living cells under physiological buffered conditions. The hybrid design combines a conventional fiber optic near-field probe with a standard atomic force microscopy cantilever. Imaging of fluorescent latex spheres suspended in an acetate matrix demonstrates the subdiffraction limited fluorescence and topography capabilities of the tips. The reduced spring constant of the hybrid tip is also shown to be amenable to measurements on living cells. NSOM fluorescence and topography measurements on living human arterial smooth muscle cells under buffered conditions are demonstrated. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Comparison of predicted ferromagnetic tendencies of Mn substituting the Ga site in III–V’s and in I–III–VI2 chalcopyrite semiconductors

    Page(s): 3753 - 3755
    Save to Project icon | PDF file iconPDF (63 KB)  

    We report density-functional calculations of the ferromagnetic (FM) stabilization energy δ=EFM-EAFM for differently oriented Mn pairs in III–V’s (GaN, GaP, GaAs) and chalcopyrite (CuGaS2, CuGaSe2, CuGaTe2) semiconductors. Ferromagnetism is found to be the universal ground state (δ≪0) in all cases. The order of FM stability in III–V’s is GaNGaPGaAs, whereas in chalcopyrites it is CuGaS2CuGaSe2CuGaTe2. Considering both groups, the order is GaNGaPGaAsCuGaS2CuGaSe2GaSbCuGaTe2. The stronger FM stabilization in III–V’s is attributed to the stronger covalent coupling between the Mn 3d and the anion p orbitals. In contrast to expectations based on Ruderman–Kittel–(Kasuya)–Yosida, (i) all Mn–Mn pair separations show FM, with no FM to antiferromagnetic oscillations and, (ii) FM is orientationally dependent, with <110> Mn–Mn pairs being the most FM. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • X-ray photoelectron spectroscopy study on SiO2/Si interface structures formed by three kinds of atomic oxygen at 300 °C

    Page(s): 3756 - 3758
    Save to Project icon | PDF file iconPDF (59 KB)  

    Using the high-brilliant synchrotron radiation at SPring-8 we have studied the SiO2/Si interface structures, the interface state densities, and the uniformities of ∼1-nm-thick oxide films formed by three kinds of atomic oxygen at 300 °C by measuring Si 2p photoelectron spectra at the photon energy of 1050 eV and the energy loss spectra of O 1s photoelectrons at the photon energy of 714 eV. Among silicon oxide films studied here the abrupt compositional transition at SiO2/Si interface, the smallest deviation in interface state density, the interface state density comparable to that for thermal oxide formed in dry oxygen at 950 °C, and the highest uniformity was obtained with oxide film formed in krypton-mixed oxygen (Kr:O2=97:3) plasma. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Electrodeless wet etching of GaN assisted with chopped ultraviolet light

    Page(s): 3759 - 3761
    Save to Project icon | PDF file iconPDF (437 KB)  

    Electrodeless photoelectrochemical (PEC) etching of GaN was studied in a K2S2O8/KOH solution irradiated with ultraviolet (UV) light either continuously or periodically. The rate of recombination of electrons and holes at dislocation defects is greater than for crystalline GaN, resulting in a rough etched surface with hexagonal pyramids. The shorter the interval of UV irradiation, the smoother is the etched GaN surface; a chopped UV source thus serves to improve the morphology of the etched surface. A uniform and smooth GaN surface was obtained with a root-mean-square roughness 0.37 nm through electrodeless PEC etching in a solution (KOH 0.01 M, K2S2O8 0.05 M) with a chopper frequency 2500 Hz (i.e., duration of irradiation 0.2 ms). © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Quantum key distribution over 122 km of standard telecom fiber

    Page(s): 3762 - 3764
    Save to Project icon | PDF file iconPDF (83 KB)  

    We report a demonstration of quantum key distribution over a standard telecom fiber exceeding 100 km in length. Through careful optimization of the interferometer and single photon detector, we achieve a quantum bit error ratio of 8.9% for a 122 km link, allowing a secure shared key to be formed after error correction and privacy amplification. Key formation rates of up to 1.9 kbit/s are achieved depending upon fiber length. We discuss the factors limiting the maximum fiber length in quantum cryptography. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Heteroepitaxial growth of wurtzite InN films on Si(111) exhibiting strong near-infrared photoluminescence at room temperature

    Page(s): 3765 - 3767
    Save to Project icon | PDF file iconPDF (131 KB)  

    High-quality InN epitaxial films have been grown by nitrogen-plasma-assisted molecular-beam epitaxy on Si(111) substrates using a double-buffer technique. Growth of a (0001)-oriented single crystalline wurtzite–InN layer was confirmed by reflection high-energy electron diffraction, x-ray diffraction, and Raman scattering. At room temperature, these films exhibited strong near-infrared (0.6–0.9 eV) photoluminescence (PL). In addition to the optical absorption measurement of absorption edge and direct band nature, the PL signal was found to depend linearly on the excitation laser intensity over a wide intensity range. These results indicate that the observed PL is due to the emission of direct band-to-band recombination rather than the band-to-defect (or impurity) deep emission. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Improved quantum efficiency in nonpolar (112¯0) AlGaN/GaN quantum wells grown on GaN prepared by lateral epitaxial overgrowth

    Page(s): 3768 - 3770
    Save to Project icon | PDF file iconPDF (83 KB)  

    Radiative and nonradiative excitonic transitions in nonpolar (112¯0) AlxGa1-xN/GaN multiple quantum wells (MQWs) grown on the GaN template prepared by lateral epitaxial overgrowth (LEO-GaN) were investigated. The structural advantages of using nonpolar orientations were confirmed by a moderate shift of the photoluminescence (PL) peak energy and negligible change in low-temperature PL lifetime with decreasing GaN well width, both of which are the results of eliminating quantum-confined Stark effects due to the polarization fields that exist in polar (0001) MQWs. Appearance of the correct in-plane light polarization and improved internal quantum efficiency for the PL peak in the MQWs on LEO-GaN were attributed to the reduction in densities of nonradiative defects and bound states. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Ferro- and piezoelectric properties of polar-axis-oriented CaBi4Ti4O15 films

    Page(s): 3771 - 3773
    Save to Project icon | PDF file iconPDF (251 KB)  

    Polar-axis-oriented CaBi4Ti4O15 (CBTi144) films were fabricated on Pt foils using a complex metal alkoxide solution. The 500-nm-thick film showed the columnar structure and consisted of well-developed grains. The a/b-axis orientation of the ferroelectric films is considered to be associated with the preferred orientation of Pt foil. The film showed good ferro- and piezoelectric properties. The Pr and Ec were 25 μC/cm2 and 306 kV/cm, respectively, at an applied voltage of 115 V. The d33 was characterized as 30 pm/V by piezoresponse force microscopy. The values were twice as large as those of the CBTi144 thin film with random orientation. The polar-axis-oriented CBTi144 films would open up possibilities for devices as Pb-free piezoelectric materials. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Two-dimensional computational model for electrochemical micromachining with ultrashort voltage pulses

    Page(s): 3774 - 3776
    Save to Project icon | PDF file iconPDF (127 KB)  

    We have developed a computational model to simulate electrochemical micromachining of conducting substrates with ultrashort voltage pulses. This theoretical approach integrates (i) a circuit model to describe charging and discharging of electrochemical double layers and electric field variation in electrolytes and (ii) the level set method to simulate feature profile evolution during electrochemical etching. Our simulation results of transient current responses and etch profile evolution are qualitatively in agreement with experimental observations. From our simulations, we find that the resolution of etched features is a strong function of the substrate double layer capacity which may be controlled by electrolyte concentration and pulse duration. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dynamics of polarization modes in photonic crystals based on arrays of vertical-cavity surface-emitting lasers

    Page(s): 3777 - 3779
    Save to Project icon | PDF file iconPDF (170 KB)  

    Polarization dynamics in coherent arrays of vertical-cavity surface-emitting lasers are studied experimentally. The two degenerate polarization lasing modes expected in infinitely large arrays are observed at different frequencies in finite-size structures. The frequency splitting increases with decreasing array size and reaches 60 GHz in 2×2 arrays. This splitting is attributed to the coupling of the two polarization states through depolarization and scattering effects at the boundary of the array. Small arrays lase in the two-frequency regime, whereas large ones oscillate in the single-frequency domain. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Characterization of phototransistor internal gain in metamorphic high-electron-mobility transistors

    Page(s): 3780 - 3782
    Save to Project icon | PDF file iconPDF (196 KB)  

    We characterize the phototransistor internal gain of metamorphic high-electron-mobility transistors (mHEMTs). When the mHEMT operates as a phototransistor, it has internal gain provided by the photovoltaic effect. To determine this internal gain, photoresponse characteristics dominated by the photoconductive effect as well as the photovoltaic effect are investigated. When the device is turned off, it acts as a photoconductor, and by calculating photoconductor gain, the primary photodetected power can be determined, which indicates the absorbed optical power. The ratio between this and the photodetected power due to the photovoltaic effect represents phototransistor internal gain. It is demonstrated that the phototransistor internal gain is function of optical modulation frequency. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Synthesis and characterization of two-layer-structured ZnO p-n homojunctions by ultrasonic spray pyrolysis

    Page(s): 3783 - 3785
    Save to Project icon | PDF file iconPDF (241 KB)  

    The two-layer-structured ZnO p-n homojunctions were prepared on single-crystal Si (100) substrate by depositing undoped n-type ZnO film on N–In codoped p-type ZnO film using ultrasonic spray pyrolysis. The crystal structure and morphology of the obtained ZnO homojunctions were examined by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. The two-layer structure was confirmed by secondary ion mass spectroscopy depth profile analysis. The current–voltage (I–V) characteristics derived from the undoped ZnO/N–In codoped ZnO two-layer structure clearly show the rectifying characteristics of typical p-n junctions. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Control of the spin polarization of photoelectrons/photoions using short laser pulses

    Page(s): 3786 - 3788
    Save to Project icon | PDF file iconPDF (83 KB)  

    We present a generic pump-probe scheme to control spin polarization of photoelectrons/photoions by short laser pulses. By coherently exciting fine structure manifolds of a multi-valence-electron system by the pump laser, a superposition of fine structure states is created. Since each fine structure state can be further decomposed into a superposition of various spin states of valence electrons, each spin component evolves differently in time. This means that varying the time delay between the pump and probe lasers leads to the control of spin states. Specific theoretical results are presented for two-valence-electron atoms, in particular for Mg, which demonstrate that not only the degree of spin polarization but also its sign can be manipulated through time delay. Since the underline physics is rather general and transparent, the presented idea may be potentially applied to nanostructures such as quantum wells and quantum dots. © 2004 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • High mobility of pentacene field-effect transistors with polyimide gate dielectric layers

    Page(s): 3789 - 3791
    Save to Project icon | PDF file iconPDF (155 KB)  

    Polyimide gate dielectric layers cured at 180 °C have been employed to fabricate high-quality pentacene field-effect transistors on polyethylenenaphthalate-based films. The surface roughness (root-mean square) of gate dielectric layers characterized by atomic force microscopy is only 0.2 nm, while that of the base film is 1 nm. The transistors with pentacene channel layers deposited on 990 nm polyimide gate dielectric layers attain the on/off ratio of 106 and mobility of 0.3 cm2/V s. Furthermore, by decreasing the thickness of polyimide gate dielectric layers down to 540 nm, the mobility is enhanced up to 1 cm2/V s. © 2004 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

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

Full Aims & Scope

Meet Our Editors

Editor
Nghi Q. Lam
Argonne National Laboratory