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Journal of Applied Physics

Issue 5 • Date Sep 2002

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Displaying Results 1 - 25 of 117
  • Issue Cover

    Page(s): c1
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  • Issue Table of Contents

    Page(s): toc1
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  • Propagation losses of the fundamental mode in a single line-defect photonic crystal waveguide on an InP membrane

    Page(s): 2227 - 2234
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    We have investigated light propagation through a single line-defect photonic crystal waveguide on a InP membrane. Modal analysis was performed using the finite-difference time-domain method. The fundamental mode has been found to be very close to the fundamental mode in a “refractive” waveguide but, in this case, it is inherently leaky. The propagation losses of this mode in the complete three-dimensional structure have been computed and measured to determine if its use could be of interest for practical applications. Propagation losses in the range of 0.1 dB/μm have been found numerically and experimentally for the fundamental mode whereas stronger out-of-plane losses have been observed for the other leaky mode within the band gap. The origins of the out-of-plane losses were then investigated and have clarified the inherent lower leakage of the fundamental mode. © 2002 American Institute of Physics. View full abstract»

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  • Effect of Eu3+ concentration on the grating efficiency and ionic conductivity in sodium–magnesium–aluminosilicate glasses

    Page(s): 2235 - 2241
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    We report a systematic study of a grating formation in which the [Eu2O3] in sodium–magnesium–aluminosilicate glasses is varied from 0.76 to 8.11 mol %. The growth, decay, and erasure of the grating are reported as functions of the [Eu2O3]. The maximum persistent change in the index of refraction was 3×10-5. The persistent change in the index of refraction was initially a quadratic function of the [Eu2O3] and showed a limiting behavior at the highest [Eu2O3]. The transient change in the index of refraction Δntran was a quadratic function of [Eu2O3] throughout the range of concentrations studied here. The grating buildup rate increased linearly with Δntran. The results of this study are consistent with the model published recently by Dixon etal Ionic conductivities were also measured to help separate the effect of the Eu3+ on the glass network from its active role in transferring the optical energy into ionic motion. © 2002 American Institute of Physics. View full abstract»

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  • High-temperature operation of a third-order mode optically pumped semiconductor laser

    Page(s): 2242 - 2247
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    Semiconductor lasers with third-order waveguide mode emission are a promising route toward compact twin-photon sources. In these structures, emission on the third-order mode is required for satisfaction of the phase-matching condition between the pumping frequency and fundamental modes at half frequency and so the production of twin photons. Phase matching depends critically on sample temperature through the dependence of the effective refractive indices of the sample. The dependence of laser mode emission on the temperature of a semiconductor structure specially designed for third-order mode emission at 775 nm is studied. It is shown that the third-order mode emission is preserved up to 40 °C whereas a contribution from other modes becomes significant above that temperature. © 2002 American Institute of Physics. View full abstract»

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  • Improvement in light-output efficiency of InGaN/GaN multiple-quantum well light-emitting diodes by current blocking layer

    Page(s): 2248 - 2250
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    The fabrication and characterization of an InGaN/GaN multiple-quantum well (MQW) light-emitting diode (LED) with a SiO2 current blocking layer inserted beneath the p-pad electrode is described. The light-output power and external quantum efficiency for the InGaN/GaN MQW LED chip with a current blocking layer were significantly increased compared to those for the conventional InGaN/GaN MQW LED chip. The increase in the light-output power can be attributed to the injection of additional current into the light-emitting quantum well layer of the LED by the SiO2 current blocking layer and a reduction in parasitic optical absorption in the p-pad electrode. © 2002 American Institute of Physics. View full abstract»

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  • Thermally induced transmission variations in ZnSe/MgF2 photonic band gap structures

    Page(s): 2251 - 2255
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    We investigate thermally induced transmission variations in a 3.6-μm-thick ZnSe/MgF2 photonic band gap structure by means of a pump–probe setup, in the 600–700 nm range, under cw pump conditions. An induced temperature increase is responsible for the thermal expansion of the layers, as well as changes in the index of refraction. As a result, the band gap structure is redshifted by several nanometers. The initial transmission of the probe beam was restored following the removal of the pump laser, thus indicating the reversible nature of the process. © 2002 American Institute of Physics. View full abstract»

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  • Accurate identification of the band gap of photonic crystals from transmission spectra

    Page(s): 2256 - 2259
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    The transmission spectra of a three-dimensional photonic crystal for various incident angles was examined. When the incident angle is not normal to the surface of the crystal, the direction of the wave vector of light is sensitive to the frequency. In order to compare the experimental band edge with the theoretical band diagram, we calculated the band diagram of the frequency versus the incident angle by converting the ordinary band diagram, which is ordinarily expressed as the diagram of the frequency versus the internal wave vector. As a result of the comparison, the changes of the band edge which was obtained in the experimental transmission measurement agreed well with the theoretical changes. It became clear that the two-step attenuation of transmission which is at large incident angles is caused by the split of the first and the second band edge (also the third and the fourth band edge) at large incident angles. © 2002 American Institute of Physics. View full abstract»

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  • Synthesized rare-earth doped oxide glasses for nonlinear optics

    Page(s): 2260 - 2268
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    Photostimulated nonlinear optical effects in synthesized PbO–Ga2O3–Bi2O3–CdO (PGBC) glasses doped by Yb3+, Er3+, and Dy3+ rare-earth (RE3+) ions were discovered. Temperature-dependent measurements of optical photoinduced second-harmonic generation (PISHG) and two-photon absorption were performed in the infrared (IR) range. CO pulse laser (λ=5.5 μm, energy power density up to 3.8 GW/cm2 per pulse) was applied as a source of IR-photoinducing and probing (fundamental) light. Absolute values of the PISHG were more than 22% higher than corresponding values obtained for other glasses: As2Te3CaCl2–PbCl2 [1] or Sb2Se3–BaCl2–PbCl2 [2] type. The investigated PGBC system possesses a shorter time response (about 18 ps), compared with other IR nonlinear optical glasses. We have also established that all nonlinear optical susceptibilities are dependent on the type of RE3+ ion. A maximal value of the PISHG is achieved for the glasses doped by Yb3+. The PISHG va- lues increase significantly below 25 K. We have carried out ab initio molecular dynamics and quantum chemical simulations in order to evaluate the possible contribution of electron–phonon anharmonic interactions in the observed phenomena. We have modeled the influence of the external CO photoinduced beam through the photoinduced anharmonic electron-phonon interactions. A decrease of the delaying time response is achieved. To obtain independent confirmation of the observed dependencies, we have carried out measurements of the Є2(E) during the external IR pumping. We have also compared the measured and theoretically calculated dependencies of the IR-induced effects. © 2002 American Institute of Physics. View full abstract»

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  • Influence of the thermodynamic equilibrium state in the excitation of samples by a plasma at atmospheric pressure

    Page(s): 2269 - 2275
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    The microwave induced plasmas have been successfully used as an excitation source in atomic emission and mass spectrometry for the analytical determination of substances. In this work a study of the influence of the thermodynamic equilibrium state over the capacity of sample excitation of an argon plasma flame sustained by a surface wave at atmospheric pressure is presented. The state of the thermodynamic equilibrium in the discharge is determined by the relation between its temperatures and densities. The values of these parameters depend on the energy available in the discharge, which is also responsible for the excitation of the samples introduced into the plasma. We have compared the behavior of two characteristic parameters of plasma (electron density and temperature) and of the ArI level population with the microwave power. The results have shown that the values of these parameters and populations had a tendency to remain constant for microwave powers above a certain value. Thus, from 100 W only a part of the energy injected into the discharge is absorbed in the plasma and the plasma equilibrium state is not consequently modified. This behavior is the same as that found for atomic lines of both halogens and iron introduced as samples into the plasma and seems to show that if the plasma is close to thermodynamic equilibrium the excitation of the samples is favored. © 2002 American Institute of Physics. View full abstract»

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  • Methane conversion into acetylene in a microwave plasma: Optimization of the operating parameters

    Page(s): 2276 - 2283
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    The methane decomposition and the formation of C2 hydrocarbons, in particular acetylene, in a microwave plasma were studied. It was found that pulsing the discharge presents major advantages over the cw operation. The effect of the operating parameters, including pressure (15–65 mbar), flow rate (33–190 sccm), and discharge power (16–81 W) was investigated, with the aim to improve the efficiency for methane conversion and to reduce the energy requirement for the formation of acetylene. Maximum values of the methane conversion degree over 90% were obtained. As a function of the discharge conditions, acetylene can become the main reaction product, with 80% selectivity. The minimum energy requirement for methane conversion was approximately 7 eV/molecule and for acetylene formation 20 eV/molecule. The results show that active species generated in the plasma contribute to the methane dissociation and influence the product distribution. The correlation between the dehydrogenation and the gas temperature supports the view of thermally activated neutral–neutral reactions. © 2002 American Institute of Physics. View full abstract»

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  • Effects of magnetic field on pulse wave forms in plasma immersion ion implantation in a radio-frequency, inductively coupled plasma

    Page(s): 2284 - 2289
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    The time-dependent current wave forms measured using a pulse biased planar electrode in hydrogen radio-frequency (rf), inductively coupled plasma, plasma immersion ion implantation experiments are observed to vary in the presence of an external magnetic field B. Results further indicate that the magnitude of the pulse current is related to the strength and direction of the magnetic field, rf power, and pressure, but the pulse current curves can be primarily correlated with B. The plasma discharges are enhanced in all cases due to magnetic confinement of the electrons, enlargement of the plasma generation volume, and increase in the rf power absorbing efficiency. The plasma density diagnosed by Langmuir probe diminishes in front of the sample chuck with B, whereas the plasma is confined nearby the sidewall of the vacuum chamber at high magnetic field. The high degree of plasma density nonuniformity at high B in front of the sample chuck is not desirable for the processing of planar samples such as silicon wafers and must be compensated. The reduction in the plasma density and plasma density gradient in the sheath can be accounted for by the changes in the pulse current wave forms. © 2002 American Institute of Physics. View full abstract»

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  • Modeling of a capacitively coupled radio-frequency methane plasma: Comparison between a one-dimensional and a two-dimensional fluid model

    Page(s): 2290 - 2295
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    A comparison is made between a one-dimensional (1D) and a two-dimensional (2D) self-consistent fluid model for a methane rf plasma, used for the deposition of diamond-like carbon layers. Both fluid models consider the same species (i.e., 20 in total; neutrals, radicals, ions, and electrons) and the same electron–neutral, ion–neutral, and neutral–neutral reactions. The reaction rate coefficients of the different electron–neutral reactions depend strongly on the average electron energy, and are obtained from the simplified Boltzmann equation. All simulations are limited to the alpha regime, hence secondary electrons are not taken into account. Whereas the 1D fluid model considers only the distance between the electrodes (axial direction), the 2D fluid model takes into account the axial as well as the radial directions (i.e., distance between the electrodes and the radius of the plasma reactor, respectively). The calculation results (species densities and species fluxes towards the electrodes) obtained with the 1D and 2D fluid model are in relatively good agreement. However, the 2D fluid model can give additional information on the fluxes towards the electrodes, as a function of electrode radius. It is found that the fluxes of the plasma species towards both electrodes show a nonuniform profile, as a function of electrode radius. This will have an effect on the uniformity of the deposited layer. © 2002 American Institute of Physics. View full abstract»

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  • Spatial population distribution of laser ablation species determined by self-reversed emission line profile

    Page(s): 2296 - 2303
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    We propose a method for determining the spatial distribution of population densities for the species in laser-produced plasma. Our method relies on the parameter fittings of the experimentally observed self-reversed emission profiles to the model which is based on the calculation of one-dimensional radiative transfer. Employed parameters in the model represent spatial distribution of emitters, absorbers, and plasma free electrons. Since the density of plasma electrons has a spatial dependence, Stark shifts and broadenings are incorporated in a position-sensitive manner. After a general description of the method, we have specifically applied it to the laser-ablated Al plasma, where Al(I) 2P2S emission line is employed for the analysis. In this specific example, we find that the accuracy of the fittings is significantly improved due to the presence of two emission lines originating from the fine structure, i. e., 2P1/22S1/2 and 2P3/22S1/2. In particular, the depth of the self-reversed structure turns out to be very sensitive to the position-dependent upper and lower level populations, which enables us to accurately determine the spatial variation of the laser-ablated species in these states. Furthermore, the calculated profile is almost unchanged with temperatures employed for fittings. This means that the present method gives reliable values of the parameters for the spatial distributions, even if the temperature is not precisely known. © 2002 American Institute of Physics. View full abstract»

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  • The addition of Sb as a surfactant to GaN growth by metal organic vapor phase epitaxy

    Page(s): 2304 - 2309
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    The role and effect of the isoelectronic center Sb on the structure and properties of GaN epilayers have been investigated. The gas phase Sb concentration was varied by changing the triethyl antimony/trimethyl gallium mole ratio over a wide range of concentrations while keeping other growth parameters constant. The Sb addition slightly improved the optical and structural properties of GaN epilayer at a low level of Sb incorporation, especially for the films grown under a high group V/III ratio conditions. The addition of Sb resulted in changes in GaN surface morphology, which was further explored by the lateral epitaxy overgrowth (LEO) technique through the changes in the growth rates and the facet formation. The presence of Sb in the gas phase greatly enhanced the lateral overgrowth rate and altered the formation of the dominant facets. Vertical facets to the LEO growth appeared with the addition of Sb under conditions that normally produced sloped sidewalls. While Sb altered the growth facet present during LEO, only a small amount of Sb was incorporated into the GaN, suggesting that Sb acts as a surfactant during the GaN metal organic vapor phase epitaxy growth. Sb addition produces surface conditions characteristic of a Ga-rich surface stoichiometry indicating both a possible change in the reactivity of NH3 and/or enhanced surface diffusion of Ga adatom species in the presence of Sb. © 2002 American Institute of Physics. View full abstract»

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  • Electron irradiation induced phase decomposition in alkaline earth multi-component oxide glass

    Page(s): 2310 - 2316
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    Electron irradiation induced phase decomposition in an alkaline earth multi-component oxide glass has been observed in a scanning transmission electron microscope. Separate regions that are rich and poor in alkaline earths form rapidly during the initial irradiation. In other words, alkaline earth multi-component oxide glasses are intolerant of high-energy (∼100 kV) electrons. This could result from the characteristics of a nonbridging O atom that bound to both Si (covalent) and alkaline earths (ionic). A modified Knotek–Feibelman model has been introduced to interpret the breakaway of cations from the glass network. Driven by electrostatic forces, the cations prefer to segregate, forming a cation rich region to reduce the amount of nonbridging O. © 2002 American Institute of Physics. View full abstract»

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  • Evolution of Ar+-damaged graphite surface during annealing as investigated by scanning probe microscopy

    Page(s): 2317 - 2322
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    The surface evolution of highly oriented pyrolytic graphite irradiated with Ar+ ions of 1.0 keV at doses between 5×1011 and 1×1013ions/cm2 during annealing was investigated by scanning tunneling microscopy (STM) and atomic force microscopy (AFM) in the tapping mode. Hillocks were observed by both STM and AFM after ion irradiation, where the height of a hillock measured by STM was larger than that measured by AFM. The ion-irradiated surface was recovered in three stages during annealing: the first stage at 473–873 K, the second stage at 873–1473 K, and the third stage at 1473–1873 K. In the first stage, many of the ion-induced hillocks recovered rapidly and irregular domelike protrusions were formed due to both the recombination of the mobile interstitial clusters with the immobile vacancies and the aggregation of interstitial clusters. In the second stage, the hillocks recovered slightly and domelike protrusions aggregated to larger domelike protrusions. In the third stage, the hillocks recovered completely and domelike protrusions changed from irregular shapes to regular circles with monatomic step height of graphite due to the change from irregular carbon interstitial clusters to complete extraplane in graphite. Hexagonal hollows were also formed and became larger circular hollows above 1623 K with monatomic step height of graphite due to the vacancy clusters formed by the migration of vacancies and the following collapse of the neighboring layers in graphite. © 2002 American Institute of Physics. View full abstract»

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  • Surface photovoltage measurements in μc-Si:H: Manifestation of the bottom space charge region

    Page(s): 2323 - 2329
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    We discuss results of surface photovoltage (U) measurements for d=10 μm thick layers of undoped hydrogenated microcrystalline silicon (μc-Si:H). By applying excitation with low energetic photons (down to 1.1 eV), i.e., with small absorption coefficient α and a large penetration depth α-1, a photovoltage peak appears on a curve U=U(α). This peak is located at α≳d-1 and its occurrence depends critically on the substrate material. The peak is present in a μc-Si:H film grown on p+ crystalline silicon (c-Si), on the other hand it is missing in the μc-Si:H samples grown on n+ c-Si or ZnO film. We present a mathematical model that enables us to link this peak to photocharge separation in the bottom space charge region at the interface μc-Si:H/substrate. Besides the magnitude of the ambipolar carrier diffusion length L, a parameter particularly critical for the occurrence of the peak turns out to be the ratio n of reverse saturation current densities of the two diodes representing surface and bottom space charge regions. The peak can be observed only when |n| is below a certain threshold value |nth|. In the simplified case when d/L≫1 and when the thicknesses of the upper and lower depletion layers can be neglected, we have found |nth|≈0.135 or 1, depending on the orientation of the top and bottom barriers to each other. However, the magnitude of the peak increases exponentially with further lowering of |n|. Therefore, the surface photovoltage method is suitable not only for evaluating the minority carrier diffusion- length L, but also for detecting the occurrence and properties of the bottom space charge region in thin film solar cells. © 2002 American Institute of Physics. View full abstract»

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  • Passivation of GaAs(110) with Ga2O3 thin films deposited by electron cyclotron resonance plasma reactive molecular beam epitaxy

    Page(s): 2330 - 2334
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    Gallium oxide thin films deposited by electron cyclotron resonance plasma molecular beam epitaxy on GaAs(110) surfaces are reported. Room temperature photoluminescence spectra show an enhancement over as-is surfaces by greater than an order of magnitude for semi-insulating wafers. This enhancement is corroborated by low temperature photoluminescence spectra, showing a reduction in AsGa, OAs, and carbon-related emissions. The bonding configuration at the interface to GaAs was investigated by x-ray photoelectron spectroscopy depth profiling and secondary ion mass spectroscopy: Arsenic oxide related compounds were below the sensitivity limits of the former technique, while carbon (both in the film and in the vicinity of the interface) was below the sensitivity limit of the latter technique. Photoluminescence enhancement is also attributed to hydrogen passivation of EL2 defects, which is found to be stable following deposition at temperatures of 400 °C on semi-insulating and p-type wafers. © 2002 American Institute of Physics. View full abstract»

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  • Physical mechanisms behind the ion-cut in hydrogen implanted silicon

    Page(s): 2335 - 2342
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    Hydrogen implanted silicon has been shown to cleave upon annealing, thus facilitating the transfer of thin silicon slices to other substrates, a process known as “ion-cut.” In our experiments <100> silicon wafers were implanted with 40 keV protons to a variety of ion doses ranging from 1×1016 to 1×1017 cm-2 and subsequently annealed at 600 °C. The samples were studied before and after annealing by a combination of Rutherford backscattering spectroscopy in channeling mode, elastic recoil detection analysis, atomic force microscopy, and electron microscopy. Mechanical stresses in the material, caused by proton irradiation, were determined by measuring changes in curvature of the silicon samples utilizing a laser scanning setup. For H doses of ≥5×1016 cm-2 ion cutting in the form of “popping off” discrete blisters was obtained. Our analyses of the cleavage mechanisms had shown that the ion-cut location in silicon is largely controlled by the lattice damage that is generated by the H implantation process. At lower H doses, the location of the cut correlates well with the damage peak and can be explained by damage induced in-plane stress and the corresponding elastic out-of-plane strain. However, at higher implantation doses the ion-cut location shifts toward a deeper region, which contains lower damage and a sufficient concentration of H. This effect can be explained by a rapid decrease of the elastic out-of-plane strain coinciding with changing fracture mechanics at high H concentrations in heavily damaged silicon. © 2002 American Institute of Physics. View full abstract»

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  • On the nature of the low-field electromagneto-plastic effect

    Page(s): 2343 - 2345
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    In the present study, reduction in the linear density of twinning dislocations resulting from the simultaneous application of high-density electric current pulses (40 A/mm2 for 400 μs) and constant magnetic field (with induction in 0.2 T) to bismuth crystals has been found. Current pulses and constant magnetic field were applied to the specimen after the deformation was introduced by a concentrated load and pileups of twinning dislocations were created. It has been clearly shown that the decrease in the linear density of twinning dislocations results in the elongation of the deformation twins. This effect occurs despite the increase of the number of twinning dislocations with an increase in the concentrated load. The experimental facts are in good accord with the modern concept of the electroplastic effect. © 2002 American Institute of Physics. View full abstract»

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  • Thermal diffusivity of porous cordierite ceramic burners

    Page(s): 2346 - 2349
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    The applicability of the laser flash method for measuring the thermal diffusivity of highly porous cordierite materials is investigated. Due to the surface roughness of the samples, some indetermination in the sample thickness measurement is produced, which induces errors in the thermal diffusivity calculation. This problem was partially overcome by attaching two thin Cu layers to both surfaces of the samples. The thermal diffusivity and conductivity values of two porous cordierite materials (40 and 50 vol % of porosity) are reported using this procedure and results are discussed comparing with data for three-layer models. © 2002 American Institute of Physics. View full abstract»

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  • Angle-dependent differential-photovoltage spectroscopy for the characterization of a GaAs/GaAlAs based vertical-cavity surface-emitting laser structure

    Page(s): 2350 - 2353
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    An angle-dependent wavelength-modulated differential-photovoltage spectroscopy (DPVS) investigation has been performed at room temperature on a bare as-grown wafer of GaAs/GaAlAs-based vertical-cavity surface-emitting laser (VCSEL) structure, designed for emitting at a wavelength near 850 nm. The differential-photovoltage (DPV) spectra exhibit both the fundamental conduction to heavy-hole excitonic transition and cavity mode plus an interference pattern related to the mirror stacks. By changing the angle of incidence in the DPV measurements the energy positions of the cavity mode and distributed Bragg reflector features show a blueshift while the excitonic transition remains unchanged. The energies of the excitonic transition and cavity mode are accurately determined from the DPV spectra. The advantages of DPVS in relation to other methods of characterizing VCSEL structures, such as surface photovoltage, photoreflectance, photocurrent, and differential photocurrent spectroscopy, are discussed. The results demonstrate considerable potential of DPVS for the nondestructive characterization of these structures at room temperature. © 2002 American Institute of Physics. View full abstract»

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  • Photonic breakdown in up-conversion imaging devices based on the integration of quantum-well infrared photodetector and light-emitting diode

    Page(s): 2354 - 2358
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    We analyze the effect of photon recycling on up-conversion in a heterostructure device including a quantum well infrared photodetector (QWIP) integrated with a light emitting diode (LED). Such a QWIP-LED device converts middle infrared radiation into near infrared (NIR) or visible radiation (VIR) utilizing intersubband transitions in the QWIP and interband transitions in the LED. We show that the reabsorption of NIR/VIR photons in the QWIP can substantially affect the up-conversion of both uniform illuminations and infrared images. As demonstrated, this effect can cause a photonic breakdown associated with a positive feedback between the emission of NIR/VIR photons from the LED and the resulting photocurrent in the QWIP. © 2002 American Institute of Physics. View full abstract»

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  • Comparison of models of electroluminescence in organic double-layer light-emitting diodes

    Page(s): 2359 - 2367
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    A theoretical model of leakage and barrier-limited recombination of charge carriers at the interface separating two disordered organic materials in organic light-emitting diodes is formulated. Spatial disorder of molecular materials is reflected in the model by differentiating the hopping distances associated with jumps leading to recombination from those leading to leakage. The former and the latter are determined by the mean intersite distance and by the shortest hopping distance, respectively. It is shown that the effect of the difference between the two hopping distances on the current and recombination efficiencies depends on a barrier height and electric field strength at the organic–organic interface. The results of the models with barrier-limited recombination and Langevin recombination are compared. It is shown that both models yield comparable results for the steady-state recombination efficiency and current, if at least one of the interfacial energy barriers is small enough and the leakage is modeled in the same way. Thus broad applicability of the Langevin model is shown, when a suggested leakage model is used. The importance of microscopic correlations in the relative positions of electrons and holes at the organic–organic interface is discussed. © 2002 American Institute of Physics. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory