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Applied Physics Letters

Issue 4 • Date Jul 2005

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Displaying Results 1 - 25 of 83
  • Issue Cover

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

    Page(s): toc1
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  • Light-induced resonant transmittance through a gold film

    Page(s): 041101 - 041101-2
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    We report the experimental observation of photoinduced resonant transmission of light through a gold film deposited on a chalcogenide glass surface. This effect is caused by the formation of a photoinduced diffraction grating in the chalcogenide glass near the gold film surface by an optical pump beam. The transmittance of a probe beam is resonantly enhanced due to grating-induced coupling to surface electromagnetic excitations on the gold film surface. This observation demonstrates the feasibility of all-optical signal processing using the extraordinary light transmission of thin metal films. View full abstract»

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  • Mechanism of the temperature sensitivity of mid-infrared GaSb-based semiconductor lasers

    Page(s): 041102 - 041102-3
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    The sources of temperature sensitivity of the threshold current in type-I and type-II mid-infrared semiconductor lasers are investigated. Measurements of the interband optical absorption allow direct comparison of the optical matrix elements in laser structures with type-I and type-II band alignments and prove that the difference in the optical matrix elements is insignificant for these two groups of structures. We show that thermally-induced hole escape from the active quantum wells strongly deteriorates the optical emission in both type heterostructures. Experiments show that the temperature decay of PL is generally stronger for type-II samples. View full abstract»

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  • Achieving 280 fs resolution with a streak camera by reducing the deflection dispersion

    Page(s): 041103 - 041103-3
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    The factors that limit the temporal resolution in a streak camera operating in an accumulative mode were studied. By controlling the timing jitter, the transit-time dispersion and the technical resolution of the camera on the order of 100 fs, the role of the deflection dispersion was investigated experimentally. It was done by changing the electron beam size in the deflection plates with a variable slit in front of the plates. The temporal resolution of the camera reached 280 fs when the slit width was a 5 μm slit. View full abstract»

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  • High-power, room-temperature, and continuous-wave operation of distributed-feedback quantum-cascade lasers at λ∼4.8 μm

    Page(s): 041104 - 041104-3
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    A high-power continuous-wave (CW) operation of distributed-feedback quantum-cascade lasers using a buried grating with epitaxial regrowth up to temperatures of above 60 °C is demonstrated. For a high-reflectivity-coated 13 μm-wide and 3 mm-long cavity, CW output powers of 135 mW at 25 °C and still 37 mW at 60 °C are obtained. The device exhibits a CW threshold current density of 1.1 kA/cm2, a maximum CW wall-plug efficiency of 1.48% at 25 °C, and a characteristic temperature of 177 K in pulsed mode. Single-mode emission near 4.8 μm with a side-mode suppression ratio of ≫30 dB and a tuning range of ∼8.1 cm-1 (i.e., tunability of 0.18 cm-1/K) in the temperature range from 15 to 60 °C is observed. View full abstract»

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  • Infrared (3.8 μm) interband cascade light-emitting diode array with record high efficiency

    Page(s): 041105 - 041105-3
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    We report here the light emission from IR interband-cascade (IC) type-II-superlattice light-emitting diode (LED) structures. We employed two different IC epitaxial structures consisting of 9 or 18 periods of active superlattice gain regions separated by multilayer injection regions. The light output (and the voltage drop) of the LEDs is observed to increase as expected with increase in the number of IC active regions. The 18-period LEDs are found to have 0.65% and 2.8% external efficiency at room temperature and liquid nitrogen temperature respectively. An increase of light intensity by 6 times is observed by thinning the GaSb substrates from 500 μm to 25 μm. Another 10% increase is observed using a linear grating on the top surface of the device. View full abstract»

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  • Photomixers fabricated on nitrogen-ion-implanted GaAs

    Page(s): 041106 - 041106-3
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    We report on fabrication and measurement of photomixers based on nitrogen-ion-implanted GaAs. We used energies of 500 keV, 700 keV, and 880 keV to implant N+ ions into GaAs substrates with an ion concentration of ∼3×1012 cm-2. The resulting material exhibited 110 fs carrier lifetime due to implantation-induced defects. Our photomixers were fabricated as metal-semiconductor-metal devices, placed at the feed point of a broadband antenna. Optoelectronic measurements were performed in the wavelength range between 350 nm and 950 nm. In comparison to their counterparts (photomixers fabricated on low-temperature-grown GaAs) the N+-implanted GaAs photomixers exhibit improvements on both the output power and responsivity. A maximal responsivity of above 100 mA/W was achieved and we did not observe any dependence of the mixer cut-off frequency on the bias voltage. These characteristics make N+-implanted GaAs the material of choice for efficient optoelectronic photomixers. View full abstract»

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  • Highly sensitive ultrafast all-optical light modulation by complex refractive-index changes in guided mode geometry composed of a photoresponsive polymer and a low-refractive-index polymer

    Page(s): 041107 - 041107-3
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    Highly sensitive ultrafast all-optical light modulation is proposed on the basis of photoinduced complex refractive-index changes in composite guided wave mode (GWM) geometry composed of a low-refractive-index polymer and a photoresponsive polymer. Both calculated and observed results indicated that reflectance, which was unity at an extinction coefficient k=0, decreased rapidly with increasing k until a certain value (kc), and increased again after that. The kc-value and the GWM dip width decreased with increasing the thickness of both polymer layers. The real-part changes shifted the GWM dip very sensitively. The low-refractive polymer contributed great improvements, such as high sensitivity and durability against a repeated femtosecond laser. The present device can give highly enhanced changes of probe light as compared with simple transmission-type devices or the GWM geometry on a metal thin film. A photoelectrochromic polymer was employed in this geometry to demonstrate ultrafast reflectance control upon femtosecond laser excitation. View full abstract»

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  • Photonic crystals for biochemical sensing in the terahertz region

    Page(s): 041108 - 041108-3
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    The propagation of terahertz waves in two-dimensional photonic-crystal waveguides was studied computationally to investigate the effects of introducing small quantities of molecules, such as deoxyribonucleic acid, into selected air holes for sensor applications. Comparison with bulk systems shows that photonic-crystal waveguides are promising for biochemical sensing. View full abstract»

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  • Fully-screened polarization-induced electric fields in blue/violet InGaN/GaN light-emitting devices grown on bulk GaN

    Page(s): 041109 - 041109-3
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    Photocurrent spectroscopy and hydrostatic-pressure-dependent electroluminescence are used to show that heavy 1×1019 cm-3 Si doping of quantum barriers is sufficient to achieve full screening of polarization-induced electric fields (PIEFs) in nitride light emitting diodes (LEDs) and laser diodes (LDs) with InGaN quantum wells. Furthermore, it is shown that at currents close to lasing threshold in nitride LDs injected charge alone is sufficient to achieve full screening of PIEFs. In contrast, full screening at low currents can only be accomplished via Si doping of quantum barriers. View full abstract»

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  • Optical enhancement of diode laser-photoacoustic trace gas detection by means of external Fabry-Perot cavity

    Page(s): 041110 - 041110-3
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    An optical enhancement method applied to a diode laser photoacoustic trace gas detector is presented. In order to improve the detection sensitivity, the light intensity inside the acoustic resonator is amplified using a Fabry-Perot cavity. A feedback signal stabilizes the laser frequency to the optical cavity length, in order to maintain the light amplification constant during the probe frequency scan. The usefulness of the optical amplifier is demonstrated by showing two ethylene spectra obtained at 1.624 μm with and without the optical enhancement. Tens to hundreds ppb (part per billion) sensibility for molecules absorbing in the region between 1.5–1.7 μm can be obtained. View full abstract»

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  • Feature of electron energy distribution in a low-pressure capacitive discharge

    Page(s): 041501 - 041501-3
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    The evolution of the electron energy distribution function is investigated in the low-pressure capacitive discharge under the collisionless electron heating regime, where the electron mean-free path is comparable to or larger than the system length. As the gas pressure decreases from 50 to 10 mTorr, a different feature of electron energy distribution with a plateau in the low-energy electron range, indicating the strong electron heating in that energy range, is found. This observed result can be explained in terms of collisionless heating from the interaction between the electron bouncing motion and the oscillating sheath [Y. M. Aliev, I. D. Kaganovich, and H. Schuter, Phys. Plasmas 4, 2413 (1997)]. A simple calculation of the electron energy distribution with the energy diffusion coefficient, including the electron bounce effect, is in good agreement with the experiment. View full abstract»

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  • Extraction of a nearly monoenergetic ion beam using a pulsed plasma

    Page(s): 041502 - 041502-3
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    A nearly monoenergetic ion beam was extracted from a capacitively coupled pulsed Ar plasma. The electron temperature decayed rapidly in the afterglow, resulting in uniform plasma potential, and minimal energy spread for ions extracted in the afterglow. Ion energy was controlled by a dc bias on a ring electrode surrounding the plasma. Langmuir probe measurements indicated that this bias simply raised the plasma potential without heating the electrons in the afterglow. A rejection grid downstream of the plasma allowed ions to pass only during a selected time window in the afterglow. The energy spread was 3.4 eV full width at half maximum for a peak ion beam energy of 102.0 eV. This energy spread is about an order of magnitude narrower than the beam extracted from the continuous plasma. View full abstract»

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  • Comparative study on emission characteristics of extreme ultraviolet radiation from CO2 and Nd:YAG laser-produced tin plasmas

    Page(s): 041503 - 041503-3
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    The direct comparison of the emission characteristics of an extreme ultraviolet (EUV) light between the CO2 and the Nd:YAG laser-produced plasmas (LPP) with a solid tin target is reported. In the case of the Nd:YAG LPP, the conversion efficiency (C.E.) peaked at a laser intensity of about 5×1010 W/cm2 and decreased at higher laser intensity. In the case of the CO2 LPP, the C.E. monotonically increased up to 2×1010 W/cm2, where the C.E. is comparable to the maximum C.E. of the Nd:YAG LPP. The spectral efficiency of the Nd:YAG LPP within the 2% bandwidth around 13.5 nm decreased with laser intensity. The corresponding spectral efficiency of the CO2 LPP was almost constant. This observation indicates the potential of the CO2 laser-produced LPP as the EUV light source for the EUV lithographic systems. View full abstract»

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  • Buckling properties of carbon nanotube bundles

    Page(s): 041901 - 041901-3
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    In the study described herein, we observed the buckling behavior of carbon nanotube (CNT) bundles under axial compression using molecular dynamics (MD) simulations. We found that the critical buckling loads of CNT bundles are much higher than that of an individual single-walled carbon nanotube (SWCNT). The addition of SWCNTs into a CNT bundle results in as much as a fivefold increase in its buckling load. The long-range van der Waals interactions also improve the overall rigidity of the CNT bundles. The larger the CNT bundle, the greater the significance of the van der Waals interactions. We also found that the buckling load of a CNT bundle is directly proportional to that of a SWCNT. View full abstract»

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  • Correlation between interfacial electronic structure and mechanical properties of ZrN–Me (MeAg, Au, or Pd) nanocomposite films

    Page(s): 041902 - 041902-3
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    Nanocomposite films of ZrN–Me (MeAg, Au, or Pd) were prepared using reactive unbalanced magnetron sputtering. The hardness and elastic modulus were measured by nanoindention and were found to vary differently with composition for the three nanocomposite structures. Young’s modulus was found to decrease much more dramatically with the increase in Me content for the ZrN–Ag system. These findings were attributed to the weaker bonding mechanism at the interface between the ceramic and the metallic phases, which is more prone to grain-boundary sliding as shown using first-principles calculations of the electronic structure at the interface for the three systems. View full abstract»

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  • Segregation of nearest-neighbor donor-pair defects to Si/SiO2 interfaces

    Page(s): 041903 - 041903-3
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    We perform first-principles density-functional calculations to study the stability of donor-pair defects at Si/SiO2 interfaces. For P dopants, individual dopant atoms energetically favor Si lattice sites in the interface region, as compared to bulk Si. When dopant atoms aggregate to the interface region at very high dopant concentrations, dopant segregation occurs in form of electrically deactivating nearest-neighbor donor pairs that comprise two threefold coordinated dopant atoms. Our defect model explains both the redistribution and deactivation of dopant atoms observed at Si/SiO2 interfaces. View full abstract»

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  • Combined synchrotron x-ray diffraction and wafer curvature measurements during Ni–Si reactive film formation

    Page(s): 041904 - 041904-3
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    Combined x-ray diffraction and wafer curvature measurements during annealing of Ni thin films (13 nm) deposited on Si (001) reveal distinct stages in stress development and silicide growth. Thanks to this unique experimental setup, a clear correlation is established between force extrema at distinct temperatures and the appearance of new silicides. It is shown that the transient formation of Ni3Si2 has a strong influence on the overall stress development. View full abstract»

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  • Raman studies of Ge-promoted stress modulation in 3C–SiC grown on Si(111)

    Page(s): 041905 - 041905-3
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    We present a study of the stress state in cubic silicon carbide (3C–SiC) thin films (120 and 300 nm) grown by solid-source molecular-beam epitaxy (SSMBE) on Si(111) substrates modified by the deposition of germanium prior to the carbonization of Si. μ-Raman measurements were used to determine the residual stress existing in the 3C–SiC layers. The stress is found to decrease linearly with increasing Ge quantity but with different strength depending on the 3C–SiC thickness deposited after the introduction of Ge. Based on secondary ions mass spectroscopy (SIMS) and transmission electron microscopy (TEM) analyses it is suggested that the Ge introduced prior to the carbonization step remains in the near-interface region and reduces the Si outdiffusion, which further reduces the stress state of the 3C–SiC layers. View full abstract»

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  • Electronic structure of wurtzite quantum dots with cylindrical symmetry

    Page(s): 041906 - 041906-3
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    This paper presents a six-band kp theory for wurtzite semiconductor nanostructures with cylindrical symmetry. Our work extends the formulation of Vahala and Sercel [Phys. Rev. Lett. 65 239 (1990)] to the Rashba-Sheka-Pikus Hamiltonian for wurtzite semiconductors, without the need for the axial approximation. Comparisons of our formulation for studying the electronic structure of wurzite quantum dots with the conventional formulation are given. View full abstract»

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  • Cross-sectional Raman spectra of InN epifilms

    Page(s): 041907 - 041907-3
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    Cross-sectional Raman spectroscopy was performed on InN epifilms. We found direct evidence for the existence of residual strain along the growth direction of the InN films. This result is very useful for the understanding of the depth dependence of the physical properties. We also found that cross-sectional Raman spectroscopy can be used to study certain vibration modes that are normally not observable in the normal surface Raman configuration. View full abstract»

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  • Frequency-dependent optical constants and conductivities of hydrogen-functionalized single-walled carbon nanotubes

    Page(s): 041908 - 041908-3
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    The frequency-dependent optical constants and electrical conductivities of hydrogen-functionalized single-walled carbon nanotubes (SWNTs) have been measured from the 0.2 to 1.5 THz region using a terahertz time domain spectroscopy. The indices of refraction and electrical conductivities of the sample after hydrogen functionalization were smaller than those of the sample before hydrogen functionalization. The experimental results were fitted using the Maxwell–Garnett model, and a reduction of plasma frequency was observed. This can be attributed to the fact that the hydrogen functionalization has reduced the number of free carriers with the bonding change from sp2 to sp3. View full abstract»

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  • Optical properties and carrier dynamics of two-dimensional electrons in AlGaN/GaN single heterostructures

    Page(s): 041909 - 041909-3
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    We have investigated the optical properties and carrier dynamics of the two-dimensional electron gas (2DEG) in Al0.4Ga0.6N/GaN single heterostructures grown by metalorganic chemical vapor deposition by means of photoluminescence (PL), PL excitation, and time-resolved PL spectroscopy. Shubnikov-de Haas oscillations were clearly observed at 1.5 K, confirming the existence of a 2DEG. An additional 2DEG PL emission appeared at about 40 meV below the GaN band-edge emission and persisted up to about 100 K, while this peak disappeared when the top Al0.4Ga0.6N layer was removed by reactive ion etching. We observed abrupt PLE absorption at GaN band edge energy and approximately 50-ps delayed risetime compared to GaN and AlGaN emissions, indicating effective carrier transfer from the GaN flatband and AlGaN regions to the heterointerface. Even though the 2DEG emission is a spatially-indirect (slow) recombination, a fast decay component of ∼0.2 ns is found to be dominant in 2DEG emission because of the fast exhaustion of photogenerated holes in GaN flatband region via spatially-direct (fast) GaN recombination. From the results, we explain the carrier generation, transfer, and recombination dynamics and the relationships between 2DEG, GaN, and Al0.4Ga0.6N emissions in undoped Al0.4Ga0.6N/GaN single heterostructures. View full abstract»

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  • Ab initio study of the structural stability of TiSi2 compounds

    Page(s): 041910 - 041910-3
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    In order to clarify the allotropic structural properties of TiSi2 we calculated by means of an ab initio density functional approach the total energies of the C49, C54, and C40 crystal structures of the bulk compound. We found that at T=0 K the C49 structure of TiSi2 is its most stable phase whereas the C54 structure, which experimentally is considered to be the ground state, is less favorable. Furthermore, by calculating the vibrational properties and the corresponding temperature dependent free energies of the three structures we predict a structural transition from C49 to C54 at about 1100 K. We also demonstrate that point defects as well as stacking faults, which are known to be present in the C49 phase, have no significant influence on the structural stability. 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