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28 Feb 2005

Volume 86, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 093101 (2005); http://dx.doi.org/10.1063/1.1870108 (3 pages)

G. S. Paraoanu and A. M. Halvari
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Numerical modeling of the induced grating autocorrelation for studying optical fiber nonlinearities in the picosecond regime

F. A. Oguama, A. Tchouassi, A. M. Johnson, and Hernando Garcia

Appl. Phys. Lett. 86, 091101 (2005); http://dx.doi.org/10.1063/1.1868069 (3 pages)

Online Publication Date: 23 February 2005

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We report a direct numerical model of the induced grating autocorrelation (IGA) based on the numerical solution of the nonlinear Schrödinger equation for an intense optical pulse that has experienced nonlinear distortion [notably, self-phase modulation (SPM) and stimulated Raman scattering (SRS)] after propagating through an optical fiber. Our numerical simulations are in good agreement with experiments. A significant advantage of the numerical approach over the well-known analytical models is its capability to predict IGA traces in the presence of pump depletion. In the light of this, IGA can now be used to study the combined effects of SPM and SRS in optical fibers in the regime where pump depletion is important, and both the nonlinear refractive index and the Raman gain coefficient of the fiber can be extracted.
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42.81.Dp Propagation, scattering, and losses; solitons
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.79.Dj Gratings
42.30.Lr Modulation and optical transfer functions

Add-drop filters utilizing vertically coupled microdisk resonators in silicon

Prakash Koonath, Tejaswi Indukuri, and Bahram Jalali

Appl. Phys. Lett. 86, 091102 (2005); http://dx.doi.org/10.1063/1.1873064 (3 pages) | Cited 14 times

Online Publication Date: 23 February 2005

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Add-drop filters, based on vertically coupled microdisk resonators, have been realized in silicon, using a modified separation by implantation of oxygen process. Buried rib waveguides in the bottom-layer silicon, of a two-layer structure, are coupled to microdisk resonators in the top-layer silicon through a silicon dioxide layer formed by oxygen implantation. The radii of the microdisk structures were varied suitably to obtain resonators with slightly shifted resonance wavelengths. The average adjacent channel crosstalk suppression of these filters exhibits an upper limit of 12.11 dB and a lower limit of 6.2 dB over the wavelength band under consideration.
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42.79.Ci Filters, zone plates, and polarizers
42.79.Gn Optical waveguides and couplers
81.16.Pr Micro- and nano-oxidation

Large plasma-edge broadened magneto-optic-polar-Kerr-effect-based broadband incoherent detection of terahertz spectral frequencies

A. De and A. Puri

Appl. Phys. Lett. 86, 091103 (2005); http://dx.doi.org/10.1063/1.1865345 (3 pages) | Cited 2 times

Online Publication Date: 23 February 2005

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A magneto-optic Kerr effect (MOKE)-based spectroscopic technique is proposed in the terahertz regime. This method relies on very large reflection edge splitting effects, which occur when the cyclotron frequency (CF) is of the same order of magnitude or greater than the plasma frequency. In the event of a very large reflection edge split, the Kerr rotation (KR) no longer occurs at the plasma edge, but instead occurs at Re(ε+ε−) ≈ 1, within the macroscopic framework of the Drude model. This implies that one can control the spectral occurrence of the MOKE resonance, simply by tuning the magnetic field strength. This phenomenon is unheard of for much shorter wavelengths, due to practical limitations on required magnetic field strengths and hence, can only be realized in the THz regime. A 3 T magnet can easily cover the proposed 0.5–5 THz spectral range for an InSb substrate. Our calculations show that in order to achieve good spectral resolution, the InSb substrate needs to be cooled to 77 K. The Kerr rotation obtained at 77 K for a CF of 1 THz is about 6.28°, which can be increased to about 18.35° by coating a thin low refractive index material on the InSb substrate. A well established ellipsometric technique, which uses four incoherent detectors, is proposed, for fast-simultaneous measurement of KR, Kerr ellipticity and reflectivity.
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78.20.Ls Magneto-optical effects
78.70.Gq Microwave and radio-frequency interactions
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
52.77.-j Plasma applications
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.50.Dn Low-field transport and mobility; piezoresistance

Triplet exciton diffusion in fac-tris(2-phenylpyridine) iridium(III)-cored electroluminescent dendrimers

Ebinazar B. Namdas, Arvydas Ruseckas, Ifor D. W. Samuel, Shih-Chun Lo, and Paul L. Burn

Appl. Phys. Lett. 86, 091104 (2005); http://dx.doi.org/10.1063/1.1867571 (3 pages) | Cited 42 times

Online Publication Date: 24 February 2005

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We have studied triplet-triplet annihilation in neat films of electrophosphorescent fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)3]-cored dendrimers containing phenylene- and carbazole-based dendrons with 2-ethylhexyloxy surface groups using time-resolved photoluminescence. From measured annihilation rates, the limiting current densities above which annihilation would dominate in dendrimer light-emitting devices are found to be >1 A/cm2. The triplet exciton diffusion length varies in the range of 2–10 nm depending on the dendron size. The distance dependence of the nearest-neighbor hopping rate shows that energy transfer is dominated by the exchange mechanism.
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85.60.Jb Light-emitting devices
78.55.Kz Solid organic materials
78.60.Fi Electroluminescence
71.70.Gm Exchange interactions
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.50.Dn Low-field transport and mobility; piezoresistance
78.66.Qn Polymers; organic compounds
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.47.-p Spectroscopy of solid state dynamics

Spectroscopic studies of molecular-beam epitaxially grown Cr2+-doped ZnSe thin films

A. Gallian, V. V. Fedorov, J. Kernal, J. Allman, S. B. Mirov, E. M. Dianov, A. O. Zabezhaylov, and I. P. Kazakov

Appl. Phys. Lett. 86, 091105 (2005); http://dx.doi.org/10.1063/1.1861952 (3 pages) | Cited 6 times

Online Publication Date: 24 February 2005

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Cr:ZnSe thin films were grown by molecular-beam epitaxy with the long-term goal of demonstrating a route for the development of transitional-metal-doped semiconductor lasers. Photoluminescence (PL) and PL lifetime measurements of doped thin films and bulk crystals indicate that Cr is incorporated in the optically active Cr2+ state up to levels of 5×1019 cm−3. The shape of PL spectra and lifetime measurements of doped thin films compares favorably with that reported for bulk samples. A microcavity formed by film interfaces is responsible for differences in spontaneous emission observed between films and bulk crystals.
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81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Et II-VI semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Ab initio study of the gas phase nucleation mechanism of GaN

Davide Moscatelli, Pierpaolo Caccioppoli, and Carlo Cavallotti

Appl. Phys. Lett. 86, 091106 (2005); http://dx.doi.org/10.1063/1.1870129 (3 pages) | Cited 3 times

Online Publication Date: 25 February 2005

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The mechanism of formation of gas phase adducts in a Ga(CH3)3–NH3 atmosphere was investigated using density functional theory and fluid dynamic simulations. We found that the GaN gas phase chemistry is dominated by a radical chain mechanism, started by the CH3· radicals originated by the decomposition of Ga(CH3)3, and resulting in the fast formation of linear covalently bonded R(GaN)x adducts. As the number of GaN units in the adduct reaches three, the molecule cyclises. A kinetic mechanism suitable to study the formation of GaN adducts was then proposed and used to simulate the chemistry in a GaN metalorganic chemical vapor deposition reactor. It was found that GaNH2 is among the most important precursors to the film growth.
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64.60.Q- Nucleation
82.60.Nh Thermodynamics of nucleation
81.05.Ea III-V semiconductors
81.15.Aa Theory and models of film growth

Polarization of III-nitride blue and ultraviolet light-emitting diodes

J. Shakya, K. Knabe, K. H. Kim, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 86, 091107 (2005); http://dx.doi.org/10.1063/1.1875751 (3 pages) | Cited 30 times

Online Publication Date: 25 February 2005

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Polarization-resolved electroluminescence studies of III-nitride blue and ultraviolet (UV) light-emitting diodes (LEDs) were performed. The LEDs were fabricated on nitride materials grown by metalorganic chemical vapor deposition on sapphire substrates (0001). Transverse electric (TE) polarization dominates in the InGaN∕GaN quantum-well (QW) blue LEDs (λ′ = 458 nm), whereas transverse magnetic (TM) polarization is dominant in the AlInGaN QW UV LEDs (λ = 333 nm). For the case of edge emission in blue LEDs, a ratio (r = I⊥/I‖) of about 1.8:1 was observed between the EL intensities with polarization E⊥c (TE mode) and E‖c (TM mode), which corresponds to a degree of polarization ∼ 0.29. The UV LEDs exhibit a ratio r of about 1:2.3, corresponding to a degree of polarization ∼ 0.4. This is due to the fact that the degree of polarization of the bandedge emission of the AlxInyGa1−x−yN active layer changes with Al concentration. The low emission efficiency of nitride UV LEDs is partly related to this polarization property. Possible consequences and ways to enhance UV emitter performances related to this unique polarization property are discussed.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.De Quantum wells
78.60.Fi Electroluminescence

Efficient drift dominated photodiodes using defected materials

Yanning Sun, Aristo Yulius, and Jerry M. Woodall

Appl. Phys. Lett. 86, 091108 (2005); http://dx.doi.org/10.1063/1.1875757 (2 pages)

Online Publication Date: 25 February 2005

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Lattice-mismatched crystal growth can result in a high density of defects, which usually degrades the performance of optoelectronic devices. We demonstrate a drift dominated photodiode, which has high responsivity even with defected material. A drift dominated InP grown on GaP substrate photodiode, with the 8% lattice mismatch, has been developed for InP on Si application. Meanwhile, a conventional p-i-n InP on GaP photodiode was also made as a control sample. Results show that with the same defected material, the drift dominated device has much higher quantum efficiencies than those of the p-i-n device, especially at short wavelengths. The internal quantum efficiencies of the drift dominated InP on GaP photodiode are higher than 70% in UV and visible region.
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85.60.Dw Photodiodes; phototransistors; photoresistors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors
61.72.S- Impurities in crystals
78.66.Fd III-V semiconductors
78.40.Fy Semiconductors
68.55.-a Thin film structure and morphology

High-performance type-II InAs/GaSb superlattice photodiodes with cutoff wavelength around 7 μm

Y. Wei, A. Hood, H. Yau, V. Yazdanpanah, M. Razeghi, M. Z. Tidrow, and V. Nathan

Appl. Phys. Lett. 86, 091109 (2005); http://dx.doi.org/10.1063/1.1879113 (3 pages) | Cited 12 times

Online Publication Date: 25 February 2005

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We report the most recent result in the area of type-II InAs/GaSb superlattice photodiodes that have a cutoff wavelength around 7 μm at 77 K. Superlattice with a period of 40 Å lattice matched to GaSb was realized using GaxIn1−x type interface engineering technique. Compared with significantly longer period superlattices, we have reduced the dark current density under reverse bias dramatically. For a 3 μm thick structure, using sulfide-based passivation, the dark current density reached 2.6×10−5 A/cm2 at −3 V reverse bias at 77 K. At this temperature the photodiodes have R0A of 9300 Ω cm2 and a thermally limited zero bias detectivity of 1×1012 cm Hz1/2/W. The 90%–10% cutoff energy width was only 16.5 meV. The devices did not show significant dark current change at 77 K after three months storage in the atmosphere.
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85.60.Dw Photodiodes; phototransistors; photoresistors
72.40.+w Photoconduction and photovoltaic effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.65.Rv Passivation

Second-order optical nonlinear and luminescent properties of Ba2TiSi2O8 nanocrystallized glass

Yoshihiro Takahashi, Kenji Kitamura, Yasuhiko Benino, Takumi Fujiwara, and Takayuki Komatsu

Appl. Phys. Lett. 86, 091110 (2005); http://dx.doi.org/10.1063/1.1879114 (3 pages) | Cited 44 times

Online Publication Date: 25 February 2005

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The optical properties of Ba2TiSi2O8 nanocrystals in transparent crystallized glasses were investigated. The transparent nanocrystallized glass with Ba2TiSi2O8 crystals having a particle size of ∼ 200 nm was fabricated by crystallization (at 760 °C for 1 h) of a glass with the stoichiometric composition of Ba2TiSi2O8, i.e., 40BaO∙20TiO2∙40SiO2 glass. Both visible second-harmonic generation (green light, 532 nm) and luminescence (blue light, ∼ 470 nm) could be observed in the transparent Ba2TiSi2O8 nanocrystallized glass, demonstrating the optical multifunctional nanocrystallized material. It was suggested that the blue luminescence from the transparent Ba2TiSi2O8 nanocrystallized glass originated from the oxygen-related defects of the SiO4 unit in the Ba2TiSi2O8 nanocrystals.
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81.05.Kf Glasses (including metallic glasses)
81.07.Bc Nanocrystalline materials
42.70.Ce Glasses, quartz
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.55.Qr Amorphous materials; glasses and other disordered solids
81.16.-c Methods of micro- and nanofabrication and processing
64.70.D- Solid-liquid transitions
81.40.Gh Other heat and thermomechanical treatments

Optical amplification in two-dimensional photonic crystals

F. Raineri, G. Vecchi, C. Cojocaru, A. M. Yacomotti, C. Seassal, X. Letartre, P. Viktorovitch, R. Raj, and A. Levenson

Appl. Phys. Lett. 86, 091111 (2005); http://dx.doi.org/10.1063/1.1879094 (3 pages) | Cited 5 times

Online Publication Date: 25 February 2005

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Optical amplification is demonstrated in a two-dimensional photonic crystal. Amplification at 1575 nm is observed in the direction normal to the plane of periodicity, by pumping the device at 810 nm. A gain up to 27 dB is measured with moderate pump fluence (50 μJ/cm2). Gain is shown to clamp as laser threshold is attained.
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42.55.Tv Photonic crystal lasers and coherent effects
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Yj Optical parametric oscillators and amplifiers
42.70.Qs Photonic bandgap materials
42.70.Hj Laser materials
42.82.Gw Other integrated-optical elements and systems

Effective plasma frequency in one-dimensional metallic-dielectric photonic crystals

Xiaochuang Xu, Yonggang Xi, Dezhuan Han, Xiaohan Liu, Jian Zi, and Ziqiang Zhu

Appl. Phys. Lett. 86, 091112 (2005); http://dx.doi.org/10.1063/1.1879101 (3 pages) | Cited 20 times

Online Publication Date: 25 February 2005

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Photonic band structures of one-dimensional (1D) metallic-dielectric photonic crystals (MDPCs) are studied theoretically. We show that a 1D MDPC can be considered as an effective metallic medium with a well-defined effective plasma frequency. This effective plasma frequency is found to be inversely proportional to the optical thickness of the dielectric layer and is independent of either the constituent metal or the thickness of the metallic layer. By increasing the optical thickness of the dielectric layer, the effective plasma frequency of a 1D MDPC can be depressed into extremely low frequencies such as far infrared or even below.
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42.70.Qs Photonic bandgap materials
77.22.Ch Permittivity (dielectric function)

Ultrafast resonant optical switching in isolated polyfluorenes chains

Tersilla Virgili, Daniele Marinotto, Guglielmo Lanzani, and Donal D.C. Bradley

Appl. Phys. Lett. 86, 091113 (2005); http://dx.doi.org/10.1063/1.1879085 (3 pages) | Cited 38 times

Online Publication Date: 25 February 2005

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Using ultrafast spectroscopy, we report evidence of monodimensional photophysics coming from isolated chains of poly(9,9-dioctylfluorene) dispersed in a polymethylmethacrylate matrix. We identify intrachain charge carriers dynamics, the decay taking place in about 1 ps. Using a three-pulse experiment we bring evidence for charges generation from higher lying states and we report an ultrafast optical gain switching in the stimulated emission region over a broad wavelength range (around 100 nm). Our experiments suggest that the expected maximum rate of on–off switching in such a molecular device can be as high as 300 GHz.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.70.Jk Polymers and organics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Erbium-doped and Raman microlasers on a silicon chip fabricated by the sol–gel process

Lan Yang, Tal Carmon, Bumki Min, Sean M. Spillane, and Kerry J. Vahala

Appl. Phys. Lett. 86, 091114 (2005); http://dx.doi.org/10.1063/1.1873043 (3 pages) | Cited 30 times

Online Publication Date: 25 February 2005

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We report high-Q sol–gel microresonators on silicon chips, fabricated directly from a sol–gel layer deposited onto a silicon substrate. Quality factors as high as 2.5×107 at 1561 nm were obtained in toroidal microcavities formed of silica sol–gel, which allowed Raman lasing at absorbed pump powers below 1 mW. Additionally, Er3+-doped microlasers were fabricated from Er3+-doped sol–gel layers with control of the laser dynamics possible by varying the erbium concentration of the starting sol–gel material. Continuous lasing with a threshold of 660 nW for erbium-doped microlaser was also obtained.
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42.55.Sa Microcavity and microdisk lasers
42.55.Ye Raman lasers
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
71.55.-i Impurity and defect levels

Interference effects in electromodulation spectroscopy applied to GaAs-based structures: A comparison of photoreflectance and contactless electroreflectance

R. Kudrawiec, P. Sitarek, J. Misiewicz, S. R. Bank, H. B. Yuen, M. A. Wistey, and James S. Harris

Appl. Phys. Lett. 86, 091115 (2005); http://dx.doi.org/10.1063/1.1873052 (3 pages) | Cited 23 times

Online Publication Date: 25 February 2005

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In this letter, we show that the oscillation features (OFs) usually observed in photoreflectance (PR) spectra of GaAs-based structures grown on the n-type GaAs substrate below the GaAs fundamental gap could be eliminated completely by applying the contactless electroreflectance (CER) instead of PR. This finding confirms that the origin of OFs is the modulation of the refractive index in the sample due to the generation of additional carriers by the modulated pump beam. In the case of CER spectroscopy, any additional carriers are not generated during the modulation hence CER spectra are free of OFs. This advantage of CER spectroscopy is very important in investigations of all structures for which OFs are present in PR spectra. In order to illustrate this advantage of CER spectroscopy we show PR and CER spectra measured first for the GaAs epilayer and next for more complicated steplike GaInNAsSb/GaNAs/GaAs quantum well structures.
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78.66.Fd III-V semiconductors
78.67.De Quantum wells
78.20.Jq Electro-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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