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Applied Physics Letters

Issue 1 • Date Jul 2003

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Displaying Results 1 - 25 of 73
  • Issue Cover

    Page(s): c1
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    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
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  • Wide-band-tunable photomixers using resonant laser-assisted field emission

    Page(s): 1 - 2
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    Simulations and experiments show a resonant interaction of tunneling electrons with a radiation field, and photomixing (optical heterodyning) in laser-assisted field emission can cause current oscillations from dc to 100 THz with this effect. Recent simulations by others are shown to be consistent with Fowler–Nordheim theory when the radiation is at low frequencies, and also confirm the existence of the resonance. The relationship of these simulations to photomixing is demonstrated, and estimates are given for the power of signals that could be obtained by this means. © 2003 American Institute of Physics. View full abstract»

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  • Narrow linewidth intervalence-band emission from germanium terahertz lasers

    Page(s): 3 - 5
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    We demonstrate narrow linewidth emission from p-Ge terahertz lasers at low magnetic fields where intervalence-band emission dominates. The volume of these laser crystals is 32 mm3, which is one order of magnitude smaller than the lasers for which the emission spectrum has been measured previously. The frequencies emitted are shown to be selected by the optical cavity and do not shift with the magnetic field, as has been observed for larger laser crystals. © 2003 American Institute of Physics. View full abstract»

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  • Ultrahigh-speed scanning near-field optical microscopy capable of over 100 frames per second

    Page(s): 6 - 8
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    Scanning near-field optical microscopy is a powerful technique offering subdiffraction-limit optical resolution. However, the range of applications is limited by slow image acquisition rates. In this letter we demonstrate an implementation of a near-field optical microscope capable of scan speeds of 150 mm/s producing images of an area 20 μm2 in less than 10 ms, i.e., over 100 frames/s. To achieve this, a method of measuring the optical near-field intensity with a high bandwidth of greater than 1 MHz has been developed. A second original aspect is that the scan system uses a mechanical resonance of the probe to address the sample. The presented microscope is over 1000 times faster than a conventional scanning near-field optical microscope and ∼10 times faster than any scanning probe microscope to date. © 2003 American Institute of Physics. View full abstract»

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  • Red emission from Eu-doped GaN luminescent films grown by metalorganic chemical vapor deposition

    Page(s): 9 - 11
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    Bright red emission has been obtained at room temperature from Eu-doped GaN films pumped by 325 nm HeCd laser. The luminescent films were grown by metalorganic chemical vapor deposition on GaN/Al2O3 substrates. Trimethylgallium (TMGa), ammonia (NH3), and europium 2,2,4,4-tetramethyl-3,5-heptanedionate were used as sources for Ga, N, and Eu dopant, respectively. The influence of the V/III ratio during growth on the photoluminescence (PL) intensity has been studied using a fixed TMGa flow rate of 92 μmol/min and varying the NH3 flow rate. The film growth rate (∼2 μm/h) is nearly constant with V/III ratio over the range from ∼30 to ∼1000. The Eu incorporation in GaN films was found to decrease with increasing V/III ratio. The Eu PL intensity (normalized to the Eu concentration) exhibited a maximum at a V/III ratio of ∼100. © 2003 American Institute of Physics. View full abstract»

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  • Standing-wave interferometer

    Page(s): 12 - 14
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    An interferometric position sensor was developed using the concept of sampling a standing wave. Interference of a standing wave created in front of a plane mirror can be detected by thin, partly transparent sensors based on amorphous silicon. The optical thickness of the absorption layer is thinner than the wavelength λ of the incident light. Detection of minima and maxima of the standing wave can be used to determine the relative displacement of the plane mirror and the detector. For determination of bidirectional fringe counting, two detectors with a certain phase shift were introduced into the standing wave. An integrated solution of two stacked n-i-p diodes and a phase shifter will be presented. The operation principle of the device will be demonstrated by measured Lissajous figures. © 2003 American Institute of Physics. View full abstract»

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  • Single-photon routing by time-division phase modulation in a Sagnac interferometer

    Page(s): 15 - 17
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    In this letter, we report the experimental demonstration of a single-photon router based on a time-division Sagnac interferometer, wherein differential phase shifts are applied on either the clockwise or counterclockwise quasi-single-photon pulses to determine the single photon interference and consequently output photon routing. High fidelity (≫85%) of single-photon routing was demonstrated over a long-distance Sagnac loop. Stable performance was guaranteed by passive compensation of stress and temperature dependent drifts of the fiber-optic path. Experimental data show that time-division single-photon routing can be realized by controlling the applied electric pulses on the integrated phase modulators in the Sagnac loop, which makes this setup suitable for a practical quantum cryptography system. © 2003 American Institute of Physics. View full abstract»

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  • High-performance and high-temperature continuous-wave-operation 1300 nm InGaAsN quantum well lasers by organometallic vapor phase epitaxy

    Page(s): 18 - 20
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    Comtinuous-wave (cw) operation of organometallic vapor phase epitaxy-grown In0.4Ga0.6As0.995N0.005 quantum well (QW) lasers has been realized, at a room-temperature near-threshold emission wavelength of 1.295 μm, with a threshold-current density of 220 A/cm2 for 2000 μm cavity-length (Lcav) devices. A threshold current density of only 615 A/cm2 was achieved for cw operation at a temperature of 100 °C, with an emission wavelength of 1.331 μm. A maximum cw-output power of 1.8 W was obtained for InGaAsN QW lasers with cavity lengths of 1000 and 2000 μm, at a heat-sink temperature of 20 °C. © 2003 American Institute of Physics. View full abstract»

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  • Two-dimensional terahertz photonic crystals fabricated by deep reactive ion etching in Si

    Page(s): 21 - 23
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    Two-dimensional terahertz photonic crystals were manufactured from Si using deep reactive ion etching. Arrays of square holes with widths of 80 (100) μm and lattice constants of 100 (125) μm were etched through 500-μm-thick wafers with high resistivity. Stop bands with transmittance ≪1% and widths ≫200 GHz were observed near 1 THz for light with an electric field vector in the plane of the wafers (TE polarization). The observed stop bands are close to TE photonic band gaps predicted by a two-dimensional calculation. © 2003 American Institute of Physics. View full abstract»

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  • Optimization of broadband quantum cascade lasers for continuous wave operation

    Page(s): 24 - 26
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    We have optimized the design of the broadband quantum cascade laser for cw operation. The improved design leads to a gain ripple of only about 4 cm-1 over more than a 0.5-μm spectral range. Simultaneous cw emission at several wavelengths spanning the range between 6.7 and 7.4 μm has been achieved in a temperature interval from 20 to 77 K. © 2003 American Institute of Physics. View full abstract»

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  • Dependence of soft x-ray conversion on atomic composition in laser produced plasma of gold–copper mix-Z targets

    Page(s): 27 - 29
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    A comparative experimental study of soft x-ray emission from laser-irradiated Au–Cu mix-Z targets of different atomic compositions has been performed. Plasma was produced from planar targets using second-harmonic laser pulses from an Nd:glass laser at a focused intensity of ∼1013W cm-2. Radiation intensity in the spectral region ∼15–150 Å and integrated x-ray yield for mix-Z target were observed to be higher than those for individual elements. The maximum conversion occurred for an atomic composition of Au 0.43–Cu 0.57. These observations are consistent with the variation of Rosseland mean opacity with atomic composition calculated using a screened hydrogenic average atom model. © 2003 American Institute of Physics. View full abstract»

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  • Surface plasmon polariton modified emission of erbium in a metallodielectric grating

    Page(s): 30 - 32
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    The spectral shape and bandwidth of the emission of Er3+ ions in silica glass around 1.5 μm is strongly modified by the presence of a silver grating. The metallodielectric grating was made by a sequence of ion implantation in silica glass, dry etching, and silver sputter deposition. Spectral enhancements are observed that are attributed to near-field coupling of Er3+ ions to surface plasmon polaritons that subsequently reradiate at well-defined resonance conditions. Qualitative agreement is observed between these resonance conditions and calculations based on the surface plasmon polariton dispersion relation. © 2003 American Institute of Physics. View full abstract»

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  • Investigation of V-Defects and embedded inclusions in InGaN/GaN multiple quantum wells grown by metalorganic chemical vapor deposition on (0001) sapphire

    Page(s): 33 - 35
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    We have examined the nature of V-defects and inclusions embedded within these defects by atomic force microscopy (AFM) and high-resolution scanning electron microscopy (SEM)/cathodoluminescence (CL) in InGaN/GaN multiple quantum wells (MQWs). To date, indium distribution nonuniformity in the well or GaN barrier growth temperature have been identified as the main factors responsible for the V-defect occurrence and propagation. Further complicating the matter, inclusions embedded within V-defects originating at the first InGaN-to-GaN interface have been observed under certain growth conditions. Our AFM and high-resolution SEM/CL findings provide evidence that some V-defects occur merely as direct results of barrier temperature growth, and that there are additional V-defects associated with In-rich regions, which act as sinks for further indium segregation during the MQW growth. Both types of V-defects have a tendency of promoting inclusions at low-temperature (800 °C) GaN barrier growth in an H2-free environment. Localized strain-energy variations associated with the apex of V-defects may be responsible for the inclusion occurrence. Adding H2 during the GaN barrier growth reduces V-defect formation and suppresses inclusion propagation entirely, rendering a uniform nanoscale CL signal. © 2003 American Institute of Physics. View full abstract»

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  • Controllable optical properties of Au/SiO2 nanocomposite induced by ultrasonic irradiation and thermal annealing

    Page(s): 36 - 38
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    Nanostructured gold/monolithic mesoporous silica assembly was synthesized by a sonochemical method. The optical absorption maximum of the as-prepared nanocomposite varies from the visible to near-infrared region, depending on the reduction rate of AuCl4- ions in solution. There exists a critical reduction rate of AuCl4- ions in solution. When the reduction rate is lower than the critical value, the absorption maximum redshifts from 560 up to 1130 nm with increase of the reduction rate; otherwise, it blueshifts. The subsequent step thermal annealing of the as-prepared nanocomposite with a maximum in the near-infrared results in a blueshift in a large region down to 550 nm. We can thus realize control of the optical absorption in a large region by ultrasonic irradiation and subsequent step thermal annealing. Further experiments reveal that the position of the absorption maximum depends on the aggregate degree of Au nanoparticles supported in the surface layer of silica and that subsequent step annealing induces disaggregation of Au nanoparticles. © 2003 American Institute of Physics. View full abstract»

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  • Blue and ultraviolet cathodoluminescence from Mn-doped epitaxial ZnO thin films

    Page(s): 39 - 41
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    Combinatorial laser molecular-beam epitaxy method was employed to fabricate epitaxial Zn1-xMnxO thin films in a high throughput fashion. Local structures around Mn were investigated for these c-axis-oriented epitaxial films by fluorescence x-ray absorption fine structure measurements. It was shown that Mn substitutionally replaces Zn in Zn1-xMnxO (x≪0.22) films. Well-structured blue and ultraviolet cathodoluminescence peaks corresponding to the intra-d-shell transitions of Mn2+ were observed, especially for smaller x. The luminescence is quenched rapidly as x is increased. By comparing the relative absorption strength per mole Mn2+ with the statistical probability of isolated Mn2+, it was concluded that the quick decrement of isolated Mn2+ with increasing x is responsible for the severe suppression of the blue and ultraviolet luminescence. © 2003 American Institute of Physics. View full abstract»

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  • Effect of implantation temperature on dislocation loop formation and origin of 1.55-μm photoluminescence from ion-beam-synthesized FeSi2 precipitates in silicon

    Page(s): 42 - 44
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    Iron implantation into Si using a metal vapor vacuum arc ion source has been performed at various temperatures to synthesize nanometer scale β-FeSi2 precipitates in Si. Transmission electron microscopy (TEM) results showed that for high-temperature-implanted samples, there were a large number of dislocation loops formed. For intermediate-temperature-implanted samples, only a row of dislocation loops located at the end of implantation range was observed. For low-temperature-implanted samples, however, no dislocation loops were observed at all. From the differences in the photoluminescence spectra, in conjunction with the TEM results, the origins of the photoluminescence peaks in different samples could be distinguished and identified to be from β-FeSi2 precipitates or from crystal defects in the samples. © 2003 American Institute of Physics. View full abstract»

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  • Visible luminescence of porous amorphous Si1-xCx:H due to selective dissolution of silicon

    Page(s): 45 - 47
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    Room-temperature photoluminescence of porous hydrogenated amorphous silicon-carbon alloys (a-Si1-xCx:H) has been studied for different carbon concentrations. Porous a-Si1-xCx:H luminesces at energies much higher than the bulk material. Secondary ion mass spectroscopy reveals that the carbon content is higher in the porous layer than in the starting material, which accounts for the blueshifting of the luminescence into the visible range. © 2003 American Institute of Physics. View full abstract»

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  • Generalized equation of phonon radiative transport

    Page(s): 48 - 50
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    We write the equation of phonon radiative transport (EPRT) and the Boltzmann transport equation by including an in-scattering term under a relaxation time approximation. The in-scattering term contains a phase function that is exactly analogous to the phase function in the equation of radiative transport (ERT), thereby making EPRT exactly same as ERT. This formulation of EPRT is called the generalized EPRT (GEPRT). GEPRT is totally consistent with EPRT and transport theory; however, GEPRT shows that the mean free path due to particle scattering depends on the acoustic thickness of the medium if scattering is anisotropic and asymmetrical for heat flow in the thickness direction of the medium, irrespective of the boundary condition. GEPRT can be solved using the techniques used for solving ERT. © 2003 American Institute of Physics. View full abstract»

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  • Mesoscale x-ray diffraction measurement of stress relaxation associated with buckling in compressed thin films

    Page(s): 51 - 53
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    Compressed thin films deposited on substrates may buckle depending on the geometrical and mechanical properties of the film/substrate set. Until recently, the small dimensions of the buckling have prevented measurements of their local in plane internal stress distribution. Using a scanning x-ray microdiffraction technique developed at a third generation x-ray synchrotron source, we obtained thin film internal stress maps for circular blisters and telephone chord buckling with micrometric spatial resolution. A fair agreement was found between the film delamination topology observed by optical microscopy and the measured stress maps. We evidenced residual stress relaxation associated with the film buckling: the top is essentially stress free while adherent region exhibits large compressive stresses. © 2003 American Institute of Physics. View full abstract»

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  • Origin of a pair of stacking faults in pseudomorphic ZnSe epitaxial layers on GaAs

    Page(s): 54 - 56
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    We have revealed the origin of typical extended defects in semiconductor heterostructures with heterovalent interfaces, namely pairs of stacking faults in pseudomorphic ZnSe epitaxial layers grown on a GaAs(001) substrate. We have taken structural images of the defects by means of high-resolution transmission electron microscopy. Analyzing the images combined with first-principles energy calculations, we have clarified the atomistic structure of the extended defects: An intrinsic stacking fault on (111) intersects the other one on (111¯) on the interface between the epitaxial layer and the substrate, forming an intersecting line along [11¯0]. Around the intersecting line, we have found that Ga, As, and Se atoms form the specific reconstructed structure with relatively low formation energy, which corresponds well to a reconstructed surface structure on GaAs(001) with excess As and additional Se atoms. We have therefore attributed the stability of extended defects to the reconstructed surface structure on the substrate formed before epitaxial growth. © 2003 American Institute of Physics. View full abstract»

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  • Practical doping principles

    Page(s): 57 - 59
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    Theoretical investigations of doping of several wide-gap materials suggest a number of rather general, practical “doping principles” that may help guide experimental strategies for overcoming doping bottlenecks. © 2003 American Institute of Physics. View full abstract»

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  • Photoluminescence enhancement by inductively coupled argon plasma exposure for quantum-well intermixing

    Page(s): 60 - 62
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    The exposure of InGaAs/InGaAsP quantum-well (QW) structures to argon (Ar) plasma in an inductively coupled system has been studied. An increase in photoluminescence (PL) intensity without PL peak shift was observed for 5-min Ar plasma exposure compared to the as-grown sample. The exposure creates point defects, and upon rapid thermal annealing produces intermixing between barriers and QWs, resulting in the blueshift of QWs. A selective intermixing using a 200-nm-thick of SiO2 layer as an intermixing mask exhibited a differential band-gap blueshift of 86 nm, with a differential linewidth broadening of 0.3 nm between masked and unmasked section. The improvement of PL intensity in combination with selective intermixing process can pave the way for high-quality hybrid photonic and optoelectronic integrated circuits. © 2003 American Institute of Physics. View full abstract»

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  • Realization of p-type ZnO thin films via phosphorus doping and thermal activation of the dopant

    Page(s): 63 - 65
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    A p-type ZnO was prepared on a sapphire substrate using P2O5 as a phosphorus dopant. As-grown n-type ZnO films doped with phosphorus showed electron concentrations of 1016–1017/cm3 and these films were converted to p-type ZnO by a thermal annealing process at a temperature above 800 °C under a N2 ambient. The electrical properties of the p-type ZnO showed a hole concentration of 1.0×1017–1.7×1019/cm3, a mobility of 0.53–3.51 cm2/V s, and a low resistivity of 0.59–4.4 Ω cm. The phosphorus-doped ZnO thin films showed a strong photoluminescence peak at 3.35 eV at 10 K, which is closely related to neutral acceptor bound excitons of the p-type ZnO. This thermal activation process was very reproducible and effective in producing phosphorus-doped p-type ZnO thin films, and the produced p-type ZnO was very stable. © 2003 American Institute of Physics. View full abstract»

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  • Luminescence decay in highly excited GaN grown by hydride vapor-phase epitaxy

    Page(s): 66 - 68
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    Carrier recombination dynamics in GaN grown by hydride vapor-phase epitaxy has been studied by means of transient photoluminescence under high photoexcitation conditions that are close to stimulated emission regime. The luminescence transient featured an exponential decay with the time constant of 205 ps at room temperature. The transient was shown to be in good agreement with a model of saturated centers of nonradiative recombination with the trap density of ∼1017 cm-3 and carrier recombination coefficients of ∼10-8 cm3/s. In such a regime, the lifetimes of electrons and holes have a common value of 410 ps. © 2003 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