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Applied Physics Letters

Issue 7 • Date Feb 1999

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Displaying Results 1 - 25 of 54
  • Issue Cover

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

    Page(s): toc1
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    Freely Available from IEEE
  • Differential carrier lifetime in oxide-confined vertical cavity lasers obtained from electrical impedance measurements

    Page(s): 899 - 901
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    Differential carrier lifetime measurements were performed on index-guided oxide-confined vertical cavity surface emitting lasers operating at 980 nm. Lifetimes were extracted from laser impedance measurements at subthreshold currents, with device size as a parameter, using a simple small-signal model. The carrier lifetimes ranged from 21 ns at 9 μA, to about 1 ns at a bias close to threshold. For a 6×6 μm2 oxide aperture device the threshold carrier density was nth∼2×1018cm-3. The effect of carrier diffusion was also considered. An ambipolar diffusion coefficient of D∼11 cm2 s-1 was obtained. © 1999 American Institute of Physics. View full abstract»

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  • Multiphoton detection using visible light photon counter

    Page(s): 902 - 904
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    Visible light photon counters feature noise-free avalanche multiplication and narrow pulse height distribution for single photon detection events. Such a well-defined pulse height distribution for a single photon detection event, combined with the fact that the avalanche multiplication is confined to a small area of the whole detector, opens up the possibility for the simultaneous detection of two photons. In this letter, we investigated this capability using twin photons generated by parametric down conversion, and present a high quantum efficiency (∼47%) detection of two photons with good time resolution (∼2 ns), which can be distinguished from a single-photon incidence with a small bit-error rate (∼0.63%). © 1999 American Institute of Physics. View full abstract»

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  • Power rise in broad-waveguide diode laser with inclined facet

    Page(s): 905 - 907
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    A method of transverse mode selection in high-power broad-waveguide separate confinement heterostructure quantum-well lasers by placing the front mirror at the angle other than the normal to the radiation propagation direction is proposed. Optimal values of facet inclination angles and widths and the refractive indices of the dielectric coating at which the fundamental guided mode dominates are found. The possibility of increasing the output power 1.2 times of a broad-waveguide separate confinement heterostructure quantum-well diode laser with inclined facet is shown. © 1999 American Institute of Physics. View full abstract»

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  • On the observation of 2.8 μm emission from diode-pumped Er3+- and Yb3+-doped low silica calcium aluminate glasses

    Page(s): 908 - 910
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    In this letter, we investigate the midinfrared photoluminescence of a series of diode-pumped Er3+-doped and Er3+, Yb3+-codoped low-silica content aluminosilicate glasses. Emission at 2.8 μm was observed in both single doped and codoped samples. The effect of Yb3+ codoping of the Er3+-doped samples was such that, for example, for a 2 wt % Er3+-doped, the photoluminescence yield at 2.8 μm was found to be roughly three times larger than that of the single 2 wt % Er3+-doped sample. This behavior was attributed to the efficient sensitization of Er3+ by Yb3+ in our oxide based host glasses. The results reported in this letter, together with the outstanding mechanical, chemical, and thermal properties of these glasses, suggest that rare-earth doped calcium aluminate glasses may become an attractive host for the development of solid state lasers operating in the midinfrared. © 1999 American Institute of Physics. View full abstract»

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  • Optical losses in plasma-etched AlGaAs microresonators using reflection spectroscopy

    Page(s): 911 - 913
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    The optical losses in dry-etched monolithic microresonators have been studied as a function of their lateral dimensions. Cylindrical microresonators with various radii have been etched from a planar GaAlAs/GaAs microcavity with a very high quality factor (Q≅11 700). Measurements of the resonance linewidth, using Ti-sapphire laser spectroscopy allowed to study the degradation of the Q factor at small radii. The Q factor is four times smaller in 1.1 μm radius microresonators, compared to the unprocessed cavity. This degradation is attributed to optical scattering from sidewalls, whose efficiency is shown to scale with the guided mode intensity at the microresonator edge. © 1999 American Institute of Physics. View full abstract»

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  • Tunable midinfrared source by difference frequency generation in bulk periodically poled KTiOPO4

    Page(s): 914 - 916
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    We demonstrate quasi-phase-matched difference frequency generation in periodically poled KTiOPO4. A midinfrared (3.2–3.4 μm) idler with a power level of 0.17 μW is generated by mixing a Nd:YAG laser and tunable external cavity laser near 1550 nm which is amplified by an erbium-doped fiber amplifier. The wavelength, temperature, and angle tuning characteristics of this device are determined. The experimental results are used to derive a Sellmeier equation with improved accuracy in the midinfrared range for the extraordinary refractive index of flux-grown KTiOPO4. © 1999 American Institute of Physics. View full abstract»

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  • Theoretical modeling of carrier and lattice heating effects for frequency chirping in semiconductor lasers

    Page(s): 917 - 919
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    A theoretical model is presented that is capable of simultaneously simulating the frequency response of the photon density, carrier density, electron temperature, hole temperature, populations of nonequilibrium longitudinal optical (LO) and transverse optical (TO) phonons at different wave vectors, and lattice temperature under the modulation of small-signal current. Our results not only provide a more consistent theoretical model for frequency chirping but also illustrate the different roles of carrier and lattice heating in the frequency response of semiconductor lasers. © 1999 American Institute of Physics. View full abstract»

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  • Unusual picosecond dynamics of a semiconductor vertical-cavity-surface-emitting laser under resonant perturbation

    Page(s): 920 - 922
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    A stationary electrically pumped semiconductor vertical cavity surface emitting laser held at T=300 K is perturbed by a femtosecond optical pulse, which is resonant with its cavity mode. For low to moderate intensities, the semiconductor laser reacts with a switch-off. Surprisingly, for yet higher pulse energies, this behavior disappears and a direct recovery of the original emission level is observed. Such behavior cannot be understood within standard or extended rate equations. We speculate that Rabi flops are important under these conditions. © 1999 American Institute of Physics. View full abstract»

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  • Ultraviolet-light-enhanced luminescence in SiC thin films grown on Si by hot filament chemical vapor deposition and ultraviolet-light-induced luminescence in anodized SiC

    Page(s): 923 - 925
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    Intense wide-band photoluminescence (PL) was observed at room temperature from both SiC thin films grown on silicon substrates by hot-filament chemical vapor deposition and anodized SiC thin films formed by electrochemical anodization in HF–ethanol solution. It was found that prolonged irradiation with ultraviolet light from a He–Cd laser (325 nm, 10 mW) generally enhanced the PL intensity of as-grown SiC but induced a new PL band in anodized SiC at room temperature. The light-induced PL emission in anodized SiC was centered at the energy between 2.1 and 2.2 eV in comparison with the initial peak position of about 1.9 eV. These effects were also temperature dependent. © 1999 American Institute of Physics. View full abstract»

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  • Tunnel contact junction native-oxide aperture and mirror vertical-cavity surface-emitting lasers and resonant-cavity light-emitting diodes

    Page(s): 926 - 928
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    Vertical-cavity surface-emitting lasers (VCSELs) and resonant-cavity light-emitting diodes (RCLEDs) are demonstrated with high index contrast distributed Bragg reflectors (DBRs) on either side of a λ-thickness cavity (λ∼980 nm). The devices, with tunnel contact junctions making possible lateral electron current excitation, have a lower 6.5 period native-oxide-based AlxOy/GaAs DBR and an upper reflector that is either a 2–4 period AlxOy/GaAs DBR, a 1–2 period SiO2/ZnSe DBR, a λ/4-thickness layer of AlxOy (antireflecting), or no mirror at all. The AlxOy/GaAs DBRs and a buried-oxide-defined current aperture are formed by selective oxidation of the high Al composition AlxGa1-xAs layers. Device characteristics are observed as a function of the upper DBR periodicity (reflectivity). Devices with upper reflectivities of R≳99% operate as VCSELs while those with less reflectivity R>~96% operate as RCLEDs, some with external differential quantum efficiencies as high as η∼27% and narrow spectral emission (Δλ∼50 Å). © 1999 American Institute of Physics. View full abstract»

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  • Diagnostics of laser ablated plasmas using fast photography

    Page(s): 929 - 931
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    We report on dynamics of the laser ablated plumes in an ambient atmosphere using fast photography. The expanding plasma is studied at different delay times with respect to the ablating pulse. Dependence of plasma parameters such as velocity, temperature, density, and pressure on time and ambient atmosphere is presented. The images of the expanding plume are used to estimate the size of the particles in the plume. © 1999 American Institute of Physics. View full abstract»

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  • Charging damage during residual metal overetching

    Page(s): 932 - 934
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    The influence of electron and ion temperatures on charging damage during residual metal (latent antenna) overetching in high-density plasmas is investigated by Monte Carlo simulations. The tunneling current through a thin gate oxide, electrically connected to the antenna, increases significantly with electron temperature, mainly as a result of changes in plasma current and ion energy distribution. However, the current decreases with ion temperature as ion shading: (a) directly decreases the ion flux to the antenna and (b) neutralizes the negative charge at the upper mask sidewalls, thus allowing more electrons to enter the pattern. The role of exposed antenna areas (trench bottoms and perimeter) is examined from the perspective of current imbalance. © 1999 American Institute of Physics. View full abstract»

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  • Photoinduced alignment control of photoreactive side-chain polymer liquid crystal by linearly polarized ultraviolet light

    Page(s): 935 - 937
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    Alignment control of mesogenic groups in a photocrosslinkable polymer liquid crystalline film was achieved by linearly polarized (LP) ultraviolet (UV) irradiation followed by heating. The alignment direction was parallel to the electric vector of the incident LPUV light and the tilt angle of the mesogenic groups could be controlled by a one-step slantwise LPUV irradiation. The photoinduced birefringence dn was 0.07 and the order parameter of the mesogenic group was 0.28. © 1999 American Institute of Physics. View full abstract»

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  • Optical anisotropy of uniaxially drawn and silver-dispersed polyimide films

    Page(s): 938 - 940
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    Distinct anisotropy in optical transmittance in the visible and near-infrared region for uniaxially drawn and silver-dispersed polyimide films was observed. The films were prepared in a one-step operation that involves thermal curing and simultaneous uniaxial drawing of poly(amic acid) (PAA) films, which were made by dissolving silver nitrate in the PAA solution at a 1:4 mol ratio. The polyimide molecular chains with a rod-like structure were oriented along the drawing direction during curing, and this orientation accompanied the generation of silver nanoparticles with elongated shapes. An anisotropy in the optical transmittance of 5:1 was obtained for a 22-μm-thick film at 850 nm with transmittance of 68% perpendicular to the drawing direction. The optical and mechanical properties of this film were retained after annealing at 300 °C for 1 h. © 1999 American Institute of Physics. View full abstract»

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  • Selective epitaxial growth of organic molecules on patterned alkali halide substrates

    Page(s): 941 - 943
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    Selective epitaxial growth of organic materials is found and analyzed. It is observed during the molecular beam epitaxy of organic molecules and charge transfer complexes on ionic surfaces. The selectivity comes from lattice matching condition on critical nuclei formation in contrast to compound semiconductors for which covalent chemical bonding plays essential roles. It can be utilized to fabricate micropatterns of crystalline organic materials accompanied by lithography processes of alkali halides using NH3 plasma. Feasibility of building three-dimensional microstructures has also been shown, which is readily applicable to make photonic crystals from optically functional organic materials. © 1999 American Institute of Physics. View full abstract»

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  • Thermomechanical properties and moisture uptake characteristics of hydrogen silsesquioxane submicron films

    Page(s): 944 - 946
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    This letter describes measurement of the biaxial modulus, coefficient of thermal expansion (CTE), and moisture uptake characteristics of hydrogen silsesquioxane (HSQ) thin films. The biaxial modulus and CTE were determined using a bending beam method, and moisture uptake was studied using a quartz crystal microbalance method. The biaxial modulus and CTE of a 0.5 μm HSQ film were measured on Si and Ge substrates and found to be 7.07 GPa and 20.5 ppm/°C, respectively. The value determined for the diffusion constant of water in a 0.7-μm-thick HSQ films is 3.61×10-10cm2/s at room temperature. © 1999 American Institute of Physics. View full abstract»

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  • Evidence for multiple atomic structure for the {101¯0} inversion domain boundaries in GaN layers

    Page(s): 947 - 949
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    Atomic structure investigation has been carried out on {101¯0} inversion domain boundaries in GaN layers grown by molecular beam epitaxy. A method based on the comparison of the stacking sequences of GaN on both sides of the boundary is proposed in order to distinguish between different models. Experimental evidence is shown for two atomic configurations of the boundary plane. Depending probably on the growth conditions, the Holt model, which has been theoretically characterized as highly energetic, can also exist for the {101¯0} inversion domain boundaries in GaN epitaxial layers. © 1999 American Institute of Physics. View full abstract»

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  • Selective area oxide desorption by electron irradiation in a H2 ambient on GaAs (100)

    Page(s): 950 - 952
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    The selective area removal of oxides from the surface of exposed GaAs (100) has been achieved by irradiating the sample with a broad, low energy electron beam in a H2 ambient. It is proposed that electrons dissociate the molecular hydrogen to create ionized species which react with the surface. The surfaces of samples decontaminated at 365 °C, up to electron energies of 200 eV, were undamaged as revealed by atomic force microscopy. Moreover, quantum well structures epitaxially grown on these surfaces exhibited luminescence. A possible reaction mechanism responsible for the oxide removal is described. © 1999 American Institute of Physics. View full abstract»

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  • Wiedemann–Franz law at boundaries

    Page(s): 953 - 954
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    The full equations are derived for the resistances to the transport of heat and electricity through boundaries of thermoelectrics. We show that the boundary resistances of heat and electricity are proportional. This relationship is a boundary form of the Wiedemann–Franz law. We also show there is a boundary Seebeck coefficient. © 1999 American Institute of Physics. View full abstract»

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  • In situ texture monitoring for growth of oriented cubic boron nitride films

    Page(s): 955 - 957
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    We report evidence for oriented growth of pure-phase cubic boron nitride on silicon (100) substrates. The films are deposited at high temperatures (up to 1200 °C) by reduced-bias ion-assisted sputtering. The growth technique produces highly textured c-BN films with relatively large grain size (∼1000 Å) and reduced residual stress as the bias voltage is decreased. We have been able to grow thick (up to 2 μm) cubic boron nitride films containing 100% of the cubic phase with the (001) crystallographic axis of c-BN oriented perpendicular to the surface of the film. We show how reflection high-energy electron diffraction applied to texture monitoring in polycrystalline films can be used as an in situ process control technique that allows texture identification and quantitative characterization of its angular spread. © 1999 American Institute of Physics. View full abstract»

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  • Morphological control and structural characteristics of crystalline Ge–C systems: Carbide nanorods, quantum dots, and epitaxial heterostructures

    Page(s): 958 - 960
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    Chemical precursors are used to grow crystalline Ge–C materials with unusual morphologies that depend on the molecular design of the precursor and the C concentration. Ge–C nanorods with overall C content of about 13–15 at. % and lattice constants close to that of pure Si grew very rapidly from the surface of a 40 nm Ge–C epitaxial film. Coherent carbide islands are formed after epitaxial growth of 20 nm Ge1-xCx (x=9 at. %) on (100)Si. Lower reaction temperatures resulted in extremely low growth rate of epitaxial Ge1-xCx (x=3–5 at. %) heterostructures with very flat surfaces implying two-dimensional layer-by-layer growth. The use of precursor chemistry as reported here to control morphology and composition in the Ge–C system may provide a simple and reliable synthetic route to a new family of Si-based heterostructures. © 1999 American Institute of Physics. View full abstract»

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  • Enhancing defect-related photoluminescence by hot implantation into SiO2 layers

    Page(s): 961 - 963
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    Visible photoluminescence around an orange band of 580 nm wavelength are observed from 300 nm thin SiO2 layers implanted by Si or Ge ions at both substrate temperatures of 25 °C [room temperature (RT)] and 400 °C (hot). Si implantations at an energy of 30 keV were performed with doses of 5×1015, 3×1016, and 1×1017cm-2 while Ge implantations were done at 100 keV with a dose of 5×1015cm-2. Samples implanted at 400 °C always show much higher intensities of luminescence than those implanted at room temperature. Electron spin resonance signals of the hot-implanted samples indicate relatively smaller amounts of nonradiative defects than those of RT-implanted samples. It is concluded that the hot-implantation effectively enhances the intensity of defect-related photoluminescence by reducing the density of the nonradiative defects and introducing the radiative defects, which contribute to the luminescence in SiO2 layers. © 1999 American Institute of Physics. View full abstract»

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  • Surface smoothing of GaAs microstructure by atomic layer epitaxy

    Page(s): 964 - 966
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    We report a method to smooth the rough surface of GaAs microstructures. This method is based on the nucleation process for atomic layer epitaxy which involves the self-limiting two-dimensional (one-monolayer) island formation. The method has been applied successfully to smooth the (111)A surfaces of chemically etched V-grooved GaAs structures as well as the (110) and (111)B side walls of selectively grown GaAs stripe structures. © 1999 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