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Applied Physics Letters

Issue 19 • Date Nov 1996

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Displaying Results 1 - 25 of 51
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Metal‐grating‐outcoupled, surface‐emitting distributed‐feedback diode lasers

    Page(s): 2795 - 2797
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    The theoretical analysis of antiphase, surface‐emitting, complex‐coupled, distributed feedback (SE‐CC‐DFB) lasers is presented. The specific configuration chosen for analysis is relatively simple: a metallic second order grating placed atop a diode‐laser structure. This type of SE‐CC‐DFB structure can be fabricated by a lift‐off and evaporation process; can operate in a single‐lobed, orthonormal beam with a rather uniform near‐field intensity pattern, and external differential quantum efficiency, ηd, values in excess of 30%. The dependence of the gain threshold on grating duty cycle for both the symmetric and antisymmetric (longitudinal) modes is presented and discussed. The external differential quantum efficiency for the symmetric mode is found to steadily increase with grating length at the expense of the degree of near‐field‐pattern uniformity. © 1996 American Institute of Physics. View full abstract»

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  • Si/SiO2 resonant cavity photodetector

    Page(s): 2798 - 2800
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    It has been shown earlier that GeSi/Si resonant‐cavity photodiodes can achieve high speed without sacrificing quantum efficiency. In this letter, we report a Si‐based resonant‐cavity photodiode that utilizes a Si/SiO2 Bragg reflector. This structure is more compatible with standard Si processing technology than the GeSi/Si resonant‐cavity photodiodes. The absorbing region is a 1‐μm‐thick polysilicon layer that has been annealed to enhance secondary grain growth and the bottom mirror consists of three quarter‐wavelength pairs of Si and SiO2. After annealing the dark current was 9 μA at 1 V, the peak quantum efficiency was 44%, and the bandwidth was ≳1.4 GHz. © 1996 American Institute of Physics. View full abstract»

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  • The origin of blue and ultraviolet emission from porous GaP

    Page(s): 2801 - 2803
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    The luminescence properties of porous n‐type GaP are reported. Apart from the orange emission of bulk GaP, emissions in the blue and ultraviolet are observed. Evidence is presented to show that this blueshifted emission is not due to quantum confinement effects, as previously suggested, but to gallium oxide on the surface of the porous material. © 1996 American Institute of Physics. View full abstract»

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  • Broad wavelength tunability of grating‐coupled external cavity midinfrared semiconductor lasers

    Page(s): 2804 - 2806
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    Midinfrared InAs‐based and GaSb‐based semiconductor lasers with wavelengths from 3.3 to 4 μm have been used in a grating‐tuned external cavity configuration. At 80 K, a tuning range up to ∼8% of the center wavelength has been obtained. Power of 0.2 W peak, 20 mW average has been demonstrated for multimode operation with ∼1–2 nm linewidth. © 1996 American Institute of Physics. View full abstract»

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  • A gratingless wavelength stabilized semiconductor laser

    Page(s): 2807 - 2809
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    A single frequency laser structure is obtained by coupling a high order mode of a semiconductor waveguide to a low index polymer waveguide. The device does not require a grating or regrowth, emits in a mode compatible with optical fibers, and may be immune to catastrophic mirror damage. The epilayers of the semiconductor waveguide use quarterwave reflectors to support a mode with a low enough effective index to phase match to the polymer waveguide. The coupling between the two waveguides is highly frequency selective and therefore stabilizes the wavelength. Preliminary structures emit in a single longitudinal and spatial mode, have 30 dB of sidemode suppression, and emit about 6 mW into a fiber compatible mode. © 1996 American Institute of Physics. View full abstract»

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  • Long wavelength infrared (λ≂11 μm) quantum cascade lasers

    Page(s): 2810 - 2812
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    AlInAs/GaInAs quantum cascade (QC) lasers operating at λ=11.2 μm wavelength are reported. In pulsed operation the peak power is in excess of 50 mW at 110 K heat sink temperature and the devices have been operated at temperatures as high as 200 K. Continuous wave single‐mode operation with powers ≂7 mW at 10 K has been achieved. This work, combined with our previous reports on QC lasers, demonstrates that these new light sources can be tailored, by suitable quantum design, over a wide wavelength range (4–11 μm) using the same heterostructure material. © 1996 American Institute of Physics. View full abstract»

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  • Second‐order nonlinearity of nonpoled polymeric thin films doped with pyrylium salts with blue window characteristics

    Page(s): 2813 - 2815
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    A novel nonlinear organic ionic material, or pyrylium salt dye, is synthesized and doped in the polymer matrix. These guest‐host‐type polymer films, which have no absorption in the blue‐wavelength region, have second harmonic generation (SHG) activities without the electric‐field poling process. The nonlinear optical coefficient d33 is estimated as 1.10 pm/V at a 15 wt % of dye concentration. The nonlinearity is stable at room temperature and at 120 °C. The SHG device is fabricated using the nonpoled polymer film, and Cerenkov‐type phase‐matched SHG is observed. © 1996 American Institute of Physics. View full abstract»

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  • Lateral self‐limitation in the laser‐induced oxidation of ultrathin metal films

    Page(s): 2816 - 2818
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    cw‐laser‐induced local oxidation of ultrathin (3–60 nm) titanium films on glass in air is studied. It is shown, that the brightening of the films upon through‐oxidation forms a negative feedback to this highly nonlinear process. It offers the possibility of stable writing of oxide line structures narrower than the diffraction limited focused laser spot. The optimum metal film thickness is of the order of the light absorption length in the metal. Transparent isolated oxide lines and gratings with periods down to 250 nm and line width down to 165 nm were recorded in 6–15 nm thick Ti films on glass by using the radiation of the Ar ion laser (λ=488, 514 nm). © 1996 American Institute of Physics. View full abstract»

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  • Diffusion and aggregation of size‐selected silver clusters on a graphite surface

    Page(s): 2819 - 2821
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    We have investigated the early stages of film growth via deposition of size‐selected silver clusters on graphite, as a function of incident cluster size. For all sizes from 50 to 250 atoms per cluster, the deposited clusters are mobile and coalesce into three‐dimensional particles with a ‘‘universal’’ diameter of ≊14 nm, possibly a consequence of lattice strain between the silver and graphite. The 14 nm particles are found mainly in small aggregates, indicating that they themselves are to some degree mobile. We have also found evidence that the particle mobility is influenced by the cluster impact angle. © 1996 American Institute of Physics. View full abstract»

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  • Spiral growth and threading dislocations for molecular beam epitaxy of PbTe on BaF2 (111) studied by scanning tunneling microscopy

    Page(s): 2822 - 2824
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    Molecular beam epitaxy of PbTe on BaF2 (111) is studied using UHV–scanning tunneling microscopy and atomic force microscopy. It is shown that PbTe growth is totally dominated by growth spirals formed around threading dislocations (TD) that originate from the growth on the 4.2% lattice‐mismatched substrate. Due to dislocation annihilation, the TD density rapidly decreases with layer thickness, which results in a dramatic increase of the electron mobilities in the layers. © 1996 American Institute of Physics. View full abstract»

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  • Growth and field emission properties of multiply twinned diamond films with quintuplet wedges

    Page(s): 2825 - 2827
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    A unique microwave plasma chemical vapor deposition (MPCVD) technique was employed to produce multiply twinned diamond films with quintuplet wedges. Biased nucleation, nonbiased growth, and high methane/hydrogen ratio (≳5%) were used to prepare the multiply twinned diamond films. The growth parameter α was carefully controlled to be close but larger than 3/2 to allow the multiply twinned particles with quintuplets to outgrow the parent face to form the secondary crystals with uniformly distributed particle sizes and smooth surface. Since there is no need to suppress the natural growth of twins in vapor‐grown diamond, higher growth rate was achieved. Excellent field emission properties of such films compared to the normal MPCVD diamond films were also obtained. © 1996 American Institute of Physics. View full abstract»

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  • Irradiation‐induced improvement of crystalline quality of epitaxially grown Ag thin films on Si substrates

    Page(s): 2828 - 2830
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    We report the Rutherford backscattering spectroscopy/channeling studies of epitaxial grown Ag films on Si(100) substrates irradiated with fast ions (12C++, 19F++, 28Si++) in the energy range between 0.5 and 4 MeV at 200 and -150 °C. The quality of the Ag films is improved considerably by ion irradiation. Irradiation with 0.5 MeV 28Si ions to 2×1016/cm2 at 200 °C, for example, reduces the channeling minimum yield from 55% to 6% at the Ag surface. The improvement of crystalline quality is brought about by a decrease in mosaic spread in the Ag film. Also, it is found that the higher the crystallinity, the more radiation‐induced defects are produced. The mechanism involved in the irradiation‐induced improvement is discussed. © 1996 American Institute of Physics. View full abstract»

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  • Tapping mode atomic force microscopy using electrostatic force modulation

    Page(s): 2831 - 2833
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    We have developed a simple tapping mode in atomic force microscopy using a capacitive electrostatic force. In this technique, the probe‐to‐sample distance is modulated by the capacitive force between tip and sample induced by a sinusoidal bias applied to the conductive probe instead of a conventional mechanical vibration. The electrostatic force versus distance curve of the probe indicates that it is necessary to use a rather stiff cantilever to prevent the snapping of the tip into the surface due to the adhesive force at the surface. We have succeeded in obtaining topographic images of a conductive surface as well as a soft polystyrene sample with a low tracking and lateral force through this method. © 1996 American Institute of Physics. View full abstract»

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  • Frequency shifts of cantilevers vibrating in various media

    Page(s): 2834 - 2836
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    A simple model is presented for rectangular cantilevers when vibrating in various media. The mass of the surrounding medium affected by the motion of the lever is calculated. It depends on the dimensions of the lever, on the excited mode, and on the density of the medium. Although the viscosity of the media is not taken into account, the resulting predictions for the resonance frequencies agree well with experimental data obtained for levers in air and water up to the seventh harmonic. © 1996 American Institute of Physics. View full abstract»

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  • Time‐resolved photoluminescence studies of InGaN epilayers

    Page(s): 2837 - 2839
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    Time‐resolved photoluminescence (PL) has been employed to study the optical transitions and their dynamic processes and to evaluate materials quality of InGaN epilayers grown by metalorganic chemical vapor deposition. Our results suggest that the PL emissions in InGaN epilayers result primarily from localized exciton recombination. The localization energies of these localized excitons have been obtained. In relatively lower quality epilayers, the localized exciton recombination lifetime τ, decreases monotonically with an increase of temperature. In high quality epilayers, τ increases with temperature at low temperatures, which is a well‐known indication of radiative exciton recombination. Our results demonstrate that time‐resolved PL measurements uniquely provide opportunities for the understanding of basic optical processes as well as for identifying high quality materials. © 1996 American Institute of Physics. View full abstract»

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  • Atomic configurations of group V acceptors in ZnSe, ZnTe, and CdTe

    Page(s): 2840 - 2842
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    The formation of donor–acceptor pairs was detected by perturbed γγ angular correlation spectroscopy. In ZnSe, ZnTe, and CdTe crystals doped with the donor 111In and one of the acceptors N, P, As, or Sb the strength of the electric field gradient shows a systematic correlation of the bond length between the respective acceptor and the neighboring cation. For N acceptors, an inward relaxation of the neighboring cations is concluded to occur. © 1996 American Institute of Physics. View full abstract»

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  • Influence of strain conditions on exciton dynamics and on thermal stability of photoluminescence of ZnCdSe/ZnSe quantum wells

    Page(s): 2843 - 2845
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    Distinctly different exciton properties in pseudomorphic and strain relaxed ZnCdSe/ZnSe structures grown on GaAs are demonstrated. For pseudomorphic or partly strained structures temperature stability of photoluminescence depends on the distance from the ZnCdSe quantum well to GaAs/ZnSe interface and less on confinement energies. Densities of two‐dimensional localized states and averaged localization energies, as seen by excitons, are determined from the photoluminescence kinetics measurements. These values are compared with the ones reported for contemporary GaAs/AlGaAs structures. © 1996 American Institute of Physics. View full abstract»

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  • Fabrication of GaAs and InAs wires in nanochannel glass

    Page(s): 2846 - 2848
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    A newly developed porous glass, nanochannel glass, was used to fabricate uniform, high‐density GaAs and InAs micro‐ and nanowires with high aspect ratios. The fabrication process utilized reactions between organogallium and organoindium compounds with arsine to produce polycrystalline GaAs and InAs with crystallite sizes of approximately 50–130 Å when annealed at 400–500 °C. At the higher annealing temperatures, the InAs wires exhibited an increase in surface porosity and grain size, whereas the GaAs wires maintained a uniform, smooth texture. © 1996 American Institute of Physics. View full abstract»

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  • Dislocations and related traps in p‐InGaAs/GaAs lattice‐mismatched heterostructures

    Page(s): 2849 - 2851
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    Dislocations and traps in p‐InGaAs/GaAs lattice‐mismatched heterostructures are investigated by cross‐section transmission electron microscopy (XTEM) and deep level transient spectroscopy (DLTS). The misfit dislocations and threading dislocations observed by XTEM in different samples with different In mole fractions and different InGaAs layer thicknesses over all satisfy the Dodson–Tsao plastic flow critical layer thickness curve. By comparing the XTEM and DLTS results, we identify that the threading dislocations in bulk layers introduce three hole trap levels H1, H2, and H5 with DLTS activation energies of 0.32, 0.40, and 0.88 eV, respectively, and one electron trap level E1 with a DLTS activation energy of 0.54 eV. The misfit dislocations in the relaxed InGaAs/GaAs interface induce a hole trap level H4 with a DLTS activation energy of 0.67–0.73 eV. © 1996 American Institute of Physics. View full abstract»

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  • Effects of vacuum annealing on the optical properties of porous silicon

    Page(s): 2852 - 2854
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    The effects of vacuum annealing on the optical absorption spectra in the visible and infrared ranges, photoluminescence intensity, and concentration of paramagnetic centers in free‐standing porous silicon films were investigated in a temperature range of 100–600 °C. It was found that heat‐induced hydrogen desorption decreased the porous silicon band gap, which suggests that band‐gap energy depends on hydrogen coverage of nanoparticles. The annealing also leads to increasing concentration of defects that were identified as silicon dangling bonds. The energy distribution of the dangling‐bond states was estimated from the absorption spectrum. © 1996 American Institute of Physics. View full abstract»

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  • Photoluminescence of copper‐doped porous silicon

    Page(s): 2855 - 2857
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    In this letter, we report the results of copper‐doped porous silicon. In the photoluminescence spectrum of porous silicon without Cu doping, only one red luminescence band appears with a peak at 676.5 nm; while in the photoluminescence spectrum of Cu‐doped porous silicon, red and near infrared luminescence bands appear with peaks at 660.6 and 802.2 nm, respectively. Energy dispersive x‐ray spectroscopy and Fourier transform infrared spectroscopy indicate the near infrared luminescence band is related to copper impurity in porous silicon. We assign the red luminescence band to band‐to‐band emission, and the near infrared luminescence band to band‐to‐acceptor emission. © 1996 American Institute of Physics. View full abstract»

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  • Effective generation‐recombination parameters in high‐energy proton irradiated silicon diodes

    Page(s): 2858 - 2860
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    The degradation of the generation and the recombination lifetime of silicon junction diodes by 10 MeV proton irradiation is compared with the introduction of the radiation‐induced deep levels. It is shown that for the fluence range studied, both the reverse current and the reciprocal lifetime increase linearly with 10 MeV H+ fluence. From this study it follows that n‐type Si is more prone to high‐energy proton irradiation damage than p‐type material. From the electrical diode characteristics, it is derived that the dominant generation center in both n‐ and p‐type Float‐Zone Si is approximately 0.12 eV from the midgap position. This strongly suggests that in both types of material, the divacancy level at Ec-0.42 eV is the dominant generation center. © 1996 American Institute of Physics. View full abstract»

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  • Group velocities in coplanar strip transmission lines on Si and Si/SiO2/Si substrates measured using differential electro‐optic sampling

    Page(s): 2861 - 2863
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    The group velocities in coplanar strip transmission lines on Si and Si/SiO2/Si substrates were compared experimentally and theoretically. To ensure the experimental accuracy, a differential electro‐optic sampling system with a delay‐time resolution of 30 fs and a spatial resolution of 1 μm has been developed. Compared with the group velocity on a Si substrate, the group velocity on a Si/SiO2/Si substrate with a 2.2 μm SiO2 layer was found to be 10% faster, which agrees well with the theoretical prediction. © 1996 American Institute of Physics. View full abstract»

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  • Sequential lateral solidification of thin silicon films on SiO2

    Page(s): 2864 - 2866
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    We report on a low‐temperature excimer‐laser‐crystallization process that produces a previously unattainable directionally solidified microstructure in thin Si films. The process involves (1) inducing complete melting of selected regions of the film via irradiation through a patterned mask, and (2) precisely controlled between‐pulse microtranslation of the sample with respect to the mask over a distance shorter than the single‐pulse lateral solidification distance, so that lateral growth can be extended over a number of iterative steps. Grains up to 200 μm in length were demonstrated; in principle, grains of unlimited length can be produced. We discuss how the technique can be extended to produce large single‐crystal regions on glass substrates. © 1996 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