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Applied Physics Letters

Issue 25 • Date Jun 2003

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Displaying Results 1 - 25 of 71
  • 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
  • Very-long wave ternary antimonide superlattice photodiode with 21 μm cutoff

    Page(s): 4411 - 4413
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    We describe a ternary antimonide superlattice photodiode with a 21 μm cutoff wavelength. The active region consists of 150 periods of 10 monolayers (MLs) of In0.07Ga0.93Sb and 19 MLs of InAs with InSb-like interfacial bonds. The device has a detectivity of 3×109 cm√Hz/W, dynamic impedance-area product of 0.18 Ω cm2, and peak external quantum efficiency of 3% at 40 K. X-ray diffraction and cross-sectional scanning tunneling microscopy show the structure to have a high degree of order with abrupt interfaces. A simulation of the absorption spectrum effectively reproduces the observed spectrum. © 2003 American Institute of Physics. View full abstract»

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  • Effects due to disorder on photonic crystal-based waveguides

    Page(s): 4414 - 4416
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    Using the multiple-scattering method, we have studied the effects of various types of disorders on the performance of two-dimensional photonic crystal-based waveguides with cylindrical inclusions. The following three types of disorders are considered: (a) all cylinders are disordered; (b) only those cylinders in the boundary layer of the waveguide are disordered; and (c) all cylinders except those in the boundary layer of the waveguide are disordered. Our results show that, for both the cases of position and size randomness, the quality of the waveguide is insensitive to the type-(c) disorder, but very sensitive to type-(a) and type-(b) disorder. We thus conclude that the uniformity of the microstructures in the boundary layer of the waveguide is vital in ensuring the functionality of the waveguide. © 2003 American Institute of Physics. View full abstract»

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  • Thermal property of tunnel-regenerated multiactive-region light-emitting diodes

    Page(s): 4417 - 4419
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    The thermal property of tunnel-regenerated multiactive-region (TRMAR) light-emitting diodes (LEDs) is studied in detail in this letter. These devices have the advantages of high quantum efficiency and high output optical power. To obtain the same output optical power, it has been shown that the thermal performance for TRMAR LEDs is much better than that of conventional ones. The heat generated from the reverse-biased tunneling junction in TRMAR LEDs is small and can be neglected as compared with heat produced from the active region as illustrated in scanning thermal microscopy result. An experimental comparison shows that the improved input power dependence on the luminescence intensity proves that TRMAR LEDs have better thermal properties than those of conventional ones. © 2003 American Institute of Physics. View full abstract»

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  • Ultrafast nonresonant third-order optical nonlinearity of a conjugated 3,3-bipyridine derivative from 1150 to 1600 nm

    Page(s): 4420 - 4422
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    A conjugated 3,3-bipyridine derivative, an apolar structure of donor–acceptor–acceptor–donor (D–A–A–D) type was designed and characterized for third-order optical nonlinearity using Z-scan technique in the wavelength range of 1150–1600 nm. Z-scan spectra reveal a positive Kerr coefficient across this wavelength range with n2=(4.6±0.7)×10-6cm2/GW at 1550 nm accompanied by negligible nonlinear absorption for wavelength around 1550 nm, indicating ideal figures of merit for applications in ultrafast all-optical switching. © 2003 American Institute of Physics. View full abstract»

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  • Third-harmonic generation of a continuous-wave Ti:Sapphire laser in external resonant cavities

    Page(s): 4423 - 4425
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    An all-solid-state tunable continuous-wave (cw) laser operating near 272 nm with a bandwidth Γ≈3 MHz has been developed. The third harmonic of light from a single-cw Ti:Sapphire laser has been generated using two external enhancement cavities. An output power of 175 mW has been produced, corresponding to an overall conversion efficiency of 8%. © 2003 American Institute of Physics. View full abstract»

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  • Highly reflective distributed Bragg reflectors using a deeply etched semiconductor/air grating for InGaN/GaN laser diodes

    Page(s): 4426 - 4428
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    High reflectivity is achieved by deeply etched InGaN/GaN distributed Bragg reflector (DBR) mirrors with tilted sidewalls, which are appropriately designed by using the finite-difference time-domain method. The predicted optimal structure is different from the simple design consisting of a λ/(4n) semiconductor and λ/4 air. If the sidewall of the grating is tilted by 4°, the reflectivity of the DBR mirrors decreases to less than 40%. However, any degradation in the reflectivity of a perfectly vertical sidewall can be suppressed to just a few percent even with a sidewall tilt of 4°, if the DBR structure is properly designed. We fabricated InGaN/GaN multiple-quantum well lasers based on the optimal design. The devices operate as lasers with optical pumping at a lower threshold than devices without DBR mirrors. The DBR mirror reflectivity is characterized by the relation between the threshold pump intensity and the inverse of the cavity length, resulting in a high reflectivity of 62%. © 2003 American Institute of Physics. View full abstract»

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  • Direct measurements of large near-band edge nonlinear index change from 1.48 to 1.55 μm in InGaAs/InAlGaAs multiquantum wells

    Page(s): 4429 - 4431
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    Direct picosecond measurements of nonlinear refractive index change and nonlinear absorption in In0.530Al0.141Ga0.329As/In0.530Ga0.470As multiquantum wells in the range 1480–1550 nm are reported. Large low-threshold nonlinear index changes are found: Δn of up to 0.14 with figure of merit of 1.38 at a fluence of 116 μJ/cm2. The index-change-over-absorption figure of merit, F, is greater than unity over much of the spectrum, pointing to the prospective applicability of the materials studied to nonlinear switching devices. © 2003 American Institute of Physics. View full abstract»

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  • Flexible low-voltage electro-optic polymer modulators

    Page(s): 4432 - 4434
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    A high-performance electro-optic (EO) polymer modulator on a flexible substrate was fabricated using a polymer substrate layer lift-off method. The SU-8 polymer has widely different adhesion properties on Si and gold substrates that makes selective lift-off possible. The flexible EO polymer modulators on a 100-μm polymer substrate layer have a Vπ of 2.6 V and extinction ratio better than 20 dB at 1550 nm. The bending loss of the flexible waveguide was unchanged at bending radii as small as 1.5 mm, and no effect on Vπ was observed for a 5 mm bending radius. © 2003 American Institute of Physics. View full abstract»

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  • Designs of terahertz waveguides for efficient parametric terahertz generation

    Page(s): 4435 - 4437
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    We show that for a slab waveguide, while pump and idler waves are weakly affected by the waveguide, their parametrically generated terahertz (THz) wave propagates in the form of multimodes. These waves may destructively interfere with one another in terms of their phases, resulting in inefficient THz parametric conversion. To avoid this problem, we designed a THz slab or rib waveguide that supports a quasi-single or single mode. Using these waveguides, the threshold powers for achieving oscillations can be significantly reduced due to the waveguide confinement of the THz waves. In addition, modal indices of refraction can be tailored for achieving phase matching without complicated periodic poling. © 2003 American Institute of Physics. View full abstract»

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  • Polarization superprism effect in surface polaritonic crystals

    Page(s): 4438 - 4440
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    Surface plasmon polariton waveguide modes excited in mutually orthogonal line defects of a surface polaritonic crystal (two-dimensional photonic crystal on a metal surface) are observed to be extremely sensitive to the polarization state of excitation light. Full switching between orthogonal waveguides can be achieved with less than 10° variation of the polarization angle. For oblique incidence, the polarization sensitivity of switching is even higher but full switching cannot be realized. This effect can be considered as a polarization-domain analog of the photonic crystal superprism effect. It suggests the possibility of building actively controlled photonic crystal devices for optical signal processing. © 2003 American Institute of Physics. View full abstract»

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  • Ultraviolet AlGaN multiple-quantum-well laser diodes

    Page(s): 4441 - 4443
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    We demonstrate ultraviolet emission from current-injection AlGaN multiple-quantum-well laser diodes grown on sapphire substrates by metalorganic chemical vapor deposition. Lasing was obtained in gain-guided laser diode test structures with uncoated facets and cavity length ranging from 400 to 1500 μm. Under pulsed bias conditions, threshold current densities as low as 23 kA/cm2 have been achieved for laser diodes with emission wavelengths between 359.7 and 361.6 nm. The maximum output power was 45 mW per facet with differential quantum efficiencies of 1.3%. © 2003 American Institute of Physics. View full abstract»

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  • Large pure refractive nonlinearity of nanostructure silica aerogel

    Page(s): 4444 - 4446
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    The nonlinear refraction coefficient of silica aerogel was estimated to be ∼-1.5×10-15m2/W (∼-3.67×10-9esu) with a signal-beam z-scan spectroscopy. The third-order nonlinear refraction coefficient of nanostructure silica aerogel was almost five orders larger than the nonlinear refraction 3) of bulk material. The large nonlinear refraction with high nonlinear figure of merit is an ideal optical property for nonlinear optical applications. © 2003 American Institute of Physics. View full abstract»

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  • Linear, segmented microdischarge array with an active length of ∼1 cm: cw and pulsed operation in the rare gases and evidence of gain on the 460.30 nm transition of Xe+

    Page(s): 4447 - 4449
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    A linear, segmented channel, microdischarge array having an ∼80×380 μm2 aperture and an active length of ∼1 cm, has been fabricated in a ceramic multilayer structure and characterized in Ne, Ar, and Xe. The length of this seven-section device is more than an order of magnitude larger than those for previous arrays (2–3 elements) of coaxial microdischarge devices, and the discharge segments are individually ballasted with integrated thick-film resistors. Pulsed and cw operation of the array for Xe pressures as large as 700 Torr has been demonstrated and experimental indications of gain on the Xe+ 6p 4D3/20→6s 4P3/2 transition at 460.30 nm are presented. This device is well suited for the excitation of microlasers, either by electron impact pumping of gases and vapors, or by photoexcitation of solid state lasers in a slab geometry. © 2003 American Institute of Physics. View full abstract»

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  • Liquid crystal alignment surface with two easy axes induced by unidirectional rubbing

    Page(s): 4450 - 4452
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    We report the liquid crystal (LC) alignment surface which has two orthogonal easy axes induced by a unidirectional rubbing treatment. When the photoreactive polymer with chalconyl sidechains is irradiated with nonpolarized UV light and subsequently rubbed with a cloth, LCs align parallel and perpendicular to the rubbing direction on the UV irradiated and nonirradiated surfaces, respectively. The polarized UV absorption of the polymer and the sign of the dichroism are measured to explain the alignment mechanism. The micropatterning of the LC alignment is successfully demonstrated through the simple process using a photomask and nonpolarized UV irradiation technique. © 2003 American Institute of Physics. View full abstract»

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  • Evolution of the electron localization in a nonconventional alloy system GaAs1-xNx probed by high-magnetic-field photoluminescence

    Page(s): 4453 - 4455
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    We demonstrate that a high magnetic field can be used effectively not only to probe the nature of the photoluminescence (PL) in a semiconductor, but also to reveal emission peaks that are unobservable at zero field since the magnetic field can alter energy relaxation processes and the statistical distribution of the photocarriers. Our systematic magneto-PL study of GaAs1-xNx (0.1%≤x≪2.5%) in fields up to 30 T indicates that the character of the low-temperature PL in this system changes drastically with varying nitrogen composition x and exhibits transitions with applying strong magnetic fields. For x≪0.7%, the PL spectrum shows many discrete features whose energies remain nearly stationary up to the highest applied field. However, the magnetic confinement gives rise to a feature emerging on the higher energy side of the zero-field spectrum. This feature does show a diamagnetic shift, but it is much slower that that of the GaAs band-edge transition. For x≫1%, the PL spectrum evolves into a broad band, and its diamagnetic shift resembles the band-edge transition in a conventional semiconductor, and the rate of shift is comparable to that of GaAs. From the diamagnetic shift of the band, the reduced effective masses for different composition of nitrogen have been derived for this system using the standard theory for the magneto-exciton in a three dimensional semiconductor. © 2003 American Institute of Physics. View full abstract»

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  • Strong ultraviolet emission from SiO2/LiNbO3(:Fe)/SiO2 structures

    Page(s): 4456 - 4458
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    SiO2/LiNbO3(LN)/SiO2 sandwich structures were fabricated for exploring efficient light emission. After annealing at 1000 °C in O2 for 30 min, this kind of sandwich structure shows a strong ultraviolet photoluminescence (PL) with an asymmetric spectral shape. This PL spectrum may be Gaussian divided into two bands peaked at 310 (α-band) and 346 nm (β-band). If the layer of LN film is replaced by an Fe-doped LN (LN:Fe) one, the β-band vanishes and the α-band redshifts. The α-band is greatly enhanced and simultaneously becomes asymmetrical after this kind of SiO2/LN:Fe/SiO2 structure is annealed for 60 min. Spectral analysis suggests that the α-band arises from an optical transition in positively charged E centers at the interfaces between the LN(:Fe) film and the two SiO2 layers, while the β-band arises from intrinsic defects in the LN(:Fe) films. The mechanism for the PL enhancement is discussed in terms of a photorefractive effect in the LN(:Fe) films. © 2003 American Institute of Physics. View full abstract»

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  • Nonuniform current distribution in metal/diamond/metal vertical structures

    Page(s): 4459 - 4461
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    The role of grain boundaries (GBs) in undoped polycrystalline diamond films has been investigated by dc and ac electrical measurements in a wide temperature range. Hopping transport along GB percolating paths and field-assisted thermal ionization of trapped charges are observed at low and high electric field strength, respectively. The temperature dependence of the ac conductivity, which reduces to a universal curve according to a random free-energy barrier model, suggests that, at low field strengths, current flow is mainly confined into GB domains in a wide temperature range. Only in the high-temperature and high-field ranges, do crystalline diamond grains become involved in current transport. © 2003 American Institute of Physics. View full abstract»

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  • Subwavelength ripple formation on the surfaces of compound semiconductors irradiated with femtosecond laser pulses

    Page(s): 4462 - 4464
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    High-spatial-frequency periodic structures on the surfaces of InP, GaP, and GaAs have been observed after multiple-pulse femtosecond laser irradiation at wavelengths in the transparency regions of the respective solids. The periods of the structures are substantially shorter than the wavelengths of the incident laser fields in the bulk materials. In contrast, high-frequency structures were not observed for laser photon energies above the band gaps of the target materials. © 2003 American Institute of Physics. View full abstract»

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  • Shortest intersubband transition wavelength (1.68 μm) achieved in AlN/GaN multiple quantum wells by metalorganic vapor phase epitaxy

    Page(s): 4465 - 4467
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    Two-hundred-period high-quality AlN/GaN multiple quantum wells (MQWs) grown by metalorganic vapor phase epitaxy are studied using high-resolution x-ray diffraction, transmission electron microscopy, and optical transmission spectroscopy. Excellent interfaces of the MQWs are confirmed by these measurements. The strong intersubband absorption peak at a wavelength of 1.68 μm is achieved for AlN (1.6 nm)/GaN(1.7 nm) MQW. The full width at half-maximum of the absorption peak is estimated to be 27 meV. © 2003 American Institute of Physics. View full abstract»

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  • Interface energy of Au7Si grown in the interfacial layer of truncated hexagonal dipyramidal Au nanoislands on polycrystalline-silicon

    Page(s): 4468 - 4470
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    Growth of truncated hexagonal dipyramidal Au nanoislands is reported by annealing Au/amorphous-Si/crystalline-Si at 1030 °C in oxygen and nitrogen ambient. Metastable gold silicide phase of Au7Si is observed to form at the interface of Au and polycrystalline Si, which was transformed from amorphous Si. Oxygen, acting as an impurity, inhibits outdiffusion of Si at the interface and thus controls the growth of Si deficient metastable phase of Au7Si in a diffusion-limited growth process. Interface energies of Au7Si (0.623–0.672 N/m) and Au–Au7Si (1.438–1.471 N/m) are derived from the contact angle measurements of the island structure involving Au and Au7Si. © 2003 American Institute of Physics. View full abstract»

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  • Inversion domains and pinholes in GaN grown over Si(111)

    Page(s): 4471 - 4473
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    High-resolution transmission electron microscopy is used to analyze the connection between pinholes and inversion domains at the AlN/GaN interface. From some pinholes on top of the AlN buffer layer, the subsequent growth of GaN was observed to lead to the formation of inversion domains. In addition, the pinhole area which was originally the termination of defects from the buffer layer is highly strained and its boundary facets in {112¯2} and {112¯3} atomic planes. Inside the GaN the inversion domain boundary quickly settles to the usual {101¯0} planes. © 2003 American Institute of Physics. View full abstract»

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  • Early manifestation of localization effects in diluted Ga(AsN)

    Page(s): 4474 - 4476
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    The electron effective mass, me, and extent of exciton wave function, rexc, were derived in GaAs1-yNy (y=0.043%–0.5%) from magnetophotoluminescence measurements. With an increase in nitrogen concentration, we find that me and rexc undergo a rapid increase and squeezing, respectively, even for y≈0.1%. This quite early manifestation of nitrogen-induced localization effects imposes important constraints on existing theoretical models. © 2003 American Institute of Physics. View full abstract»

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  • Effect of InGaAs capping layer on the properties of InAs/InGaAs quantum dots and lasers

    Page(s): 4477 - 4479
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    We report the effects of In0.33Ga0.67As capping layers on the structural and optical properties of InAs self-organized quantum dots grown by gas-source molecular-beam epitaxy. With different deposition methods for the InGaAs capping layer, the quantum-dot density can be adjusted from 2.3×1010 to 1.7×1011cm-2. As-cleaved 3.98-mm-long diode laser using triple stacks of InAs quantum dots with the capping layer grown by GaAs/InAs sequential binary growth demonstrates an emission wavelength of 1305 nm and a threshold current density of 360 A/cm2. A ground-state saturation gain of 16.6 cm-1 is achieved due to the high dot density. © 2003 American Institute of Physics. View full abstract»

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Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics.

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Nghi Q. Lam
Argonne National Laboratory