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10 Jan 2005

Volume 86, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 021101 (2005); http://dx.doi.org/10.1063/1.1849439 (3 pages)

H. W. Choi, C. W. Jeon, C. Liu, I. M. Watson, M. D. Dawson, P. R. Edwards, R. W. Martin, S. Tripathy, and S. J. Chua
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InGaN nano-ring structures for high-efficiency light emitting diodes

H. W. Choi, C. W. Jeon, C. Liu, I. M. Watson, M. D. Dawson, P. R. Edwards, R. W. Martin, S. Tripathy, and S. J. Chua

Appl. Phys. Lett. 86, 021101 (2005); http://dx.doi.org/10.1063/1.1849439 (3 pages) | Cited 18 times

Online Publication Date: 30 December 2004

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A technique based on the Fresnel diffraction effect for the fabrication of nano-scale site-controlled ring structures in InGaN/GaN multi-quantum well structures has been demonstrated. The ring structures have an internal diameter of 500 nm and a wall width of 300 nm. A 1 cm−1 Raman shift has been measured, signifying substantial strain relaxation from the fabricated structure. The 9 nm blueshift observed in the cathodoluminescence spectra can be attributed to band filling and/or screening of the piezoelectric field. A light emitting diode based on this geometry has been demonstrated.
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81.07.Bc Nanocrystalline materials
81.05.Ea III-V semiconductors
81.16.Nd Micro- and nanolithography
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Rf Micro- and nanoscale pattern formation
78.60.Hk Cathodoluminescence, ionoluminescence
62.25.-g Mechanical properties of nanoscale systems
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Fs III-V and II-VI semiconductors

AlGaInP laser diodes incorporating a 3λ/4 multiple quantum barrier

A. Sobiesierski, I. C. Sandall, P. M. Smowton, P. Blood, A. B. Krysa, M. R. Brown, K. S. Teng, and S. P. Wilks

Appl. Phys. Lett. 86, 021102 (2005); http://dx.doi.org/10.1063/1.1849847 (3 pages) | Cited 4 times

Online Publication Date: 30 December 2004

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Using segmented contact measurements to determine gain versus quasi-Fermi level separation and nonradiative recombination we demonstrate that placing a multiquantum barrier (MQB) within the p-type cladding of 670 nm AlGaInP laser diodes reduces electron leakage current as a function of quasi-Fermi level separation compared to otherwise identical reference devices. At 300 K, where thermally activated leakage is absent, devices with and without a MQB have the same threshold current density whereas at 375 K the threshold current density of a 320 μm laser is reduced by 1735±113 A cm−2 for the device containing the MQB.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

High-Q whispering-gallery modes in GaAs/AlOx microdisks

E. Peter, I. Sagnes, G. Guirleo, S. Varoutsis, J. Bloch, A. Lemaître, and P. Senellart

Appl. Phys. Lett. 86, 021103 (2005); http://dx.doi.org/10.1063/1.1844033 (3 pages) | Cited 10 times

Online Publication Date: 30 December 2004

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We report on the fabrication of microdisks on an AlOx pedestal. We develop a process using electron beam lithography, a chemical etching, and selective oxidation. InAs self-assembled quantum dots are used as a broad band source to probe the optical modes of the microdisks. With this process, we observe whispering-gallery modes, with quality factors as large as 12 500 for 2-μm-diam microdisks.
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81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials
81.16.Nd Micro- and nanolithography
78.55.Cr III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
81.65.Mq Oxidation
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Y1-xEuxCa4O(BO3)3 thin film as a luminescent material screened by the combinatorial method

Hiroyuki Sano, Takahiro Matsumoto, Yuji Matsumoto, and Hideomi Koinuma

Appl. Phys. Lett. 86, 021104 (2005); http://dx.doi.org/10.1063/1.1844044 (3 pages) | Cited 3 times

Online Publication Date: 30 December 2004

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A phosphor material, Y1-xEuxCa4O(BO3)3 (0 ⩽ x ⩽ 1) film, was fabricated on SiO2 substrates by the combinatorial laser molecular-beam epitaxy method. Photoluminescence (PL) and PL decay were measured for this film library to identify the optimum composition as well as to determine the luminescence mechanism. Results showed that the observed intense emission peak at 615 nm originated from the electric dipole math→math transition of Eu3+. This strong emission makes this red phosphor particularly applicable in devices such as plasma display panels and Xe lamps.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials

Coherent array of white-light continuum filaments produced by diffractive microlenses

K. Cook, R. McGeorge, A. K. Kar, M. R. Taghizadeh, and R. A. Lamb

Appl. Phys. Lett. 86, 021105 (2005); http://dx.doi.org/10.1063/1.1848180 (3 pages) | Cited 7 times

Online Publication Date: 30 December 2004

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The generation of a regular arrangement of stable, coherent white-light continuum filaments in B270 crown glass is observed by using an array of diffractive microlenses. Each lens allows the formation of between one and four filaments originating from aberrations induced by the focusing geometry. These filament groups generate very stable interference fringes in the far field.
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42.79.Bh Lenses, prisms and mirrors
42.70.Ce Glasses, quartz

All-epitaxial, lithographically defined, current- and mode-confined vertical-cavity surface-emitting laser based on selective interfacial fermi-level pinning

J. Ahn, D. Lu, and D. G. Deppe

Appl. Phys. Lett. 86, 021106 (2005); http://dx.doi.org/10.1063/1.1849417 (3 pages) | Cited 5 times

Online Publication Date: 3 January 2005

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An approach is presented to fabricate a current- and mode-confined vertical-cavity surface-emitting laser that is all-epitaxial and lithographically defined. The device uses selective Fermi level pinning to self-align the electrical injection to a mode-confining intracavity phase-shifting mesa.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.40.Hp Lithography, masks and pattern transfer
73.21.Fg Quantum wells

Stable and efficient electrophosphorescent organic light-emitting devices grown by organic vapor phase deposition

Theodore X. Zhou, Tan Ngo, Julie J. Brown, Max Shtein, and Stephen R. Forrest

Appl. Phys. Lett. 86, 021107 (2005); http://dx.doi.org/10.1063/1.1849841 (3 pages) | Cited 15 times

Online Publication Date: 3 January 2005

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An electrophosphorescent organic light-emitting device (PHOLED™) employing fac-tris(2-phenylpyridine)iridium [Ir(ppy)3] as the green emitting phosphor has been fabricated using a pilot-production organic vapor phase deposition (OVPD™) system. Highly controlled mass transport of the organic vapor to the substrate results in deposition rates of over 10 Å/s and spatial uniformity better than ±2% across a 150 mm×150 mm substrate with less than ±2% run-to-run variations. The device current–voltage, luminous efficiency, and operational lifetime performances are compared to those of a similar device grown by conventional vacuum thermal evaporation (VTE). The green OVPD-grown PHOLED exhibits a maximum external quantum efficiency of (7.0±0.1)% at a luminance of 1000 cd/m2, comparable to the VTE device performance. The operational lifetime of the OVPD-grown devices was found to be comparable to or even somewhat longer than the lifetime achieved by VTE. Furthermore, PHOLEDs with emissive layers deposited at 4.8 and 10.8 Å/s are compared, and demonstrate equivalent performance.
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85.60.Jb Light-emitting devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.66.Qn Polymers; organic compounds
73.61.Ph Polymers; organic compounds

Lasing characteristics of InGaAs/InGaAsP multiple-quantum-well waveguide-type depleted optical thyristor with vertical window

Woon Kyung Choi, Doo Gun Kim, Young Wan Choi, Seok Lee, Deok Ha Woo, and Sun Ho Kim

Appl. Phys. Lett. 86, 021108 (2005); http://dx.doi.org/10.1063/1.1850184 (3 pages)

Online Publication Date: 3 January 2005

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This study demonstrates the lasing characteristics of InGaAs/InGaAsP multiple-quantum-well waveguide-type depleted optical thyristor using the vertical window. The measured switching voltage and current are 3.36 V and 10 μA, respectively. The lasing threshold current is 131 mA at 25 °C. The output peak wavelength is 1570 nm at a bias current of 1.22 Ith and there is no input signal. The vertically injected depleted optical thyristor shows very good isolation between input and output signals.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.-q Optoelectronic devices
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Magnetic field tunable circularly polarized stimulated emission from midinfrared IV-VI vertical emitting lasers

J. Fürst, H. Pascher, T. Schwarzl, G. Springholz, M. Böberl, G. Bauer, and W. Heiss

Appl. Phys. Lett. 86, 021109 (2005); http://dx.doi.org/10.1063/1.1851609 (3 pages)

Online Publication Date: 4 January 2005

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Optically pumped laser emission from a midinfrared PbSe vertically emitting microcavity structure in a magnetic field applied in Faraday geometry is presented. It is shown that the emission line at a wavelength of about 7.9 μm splits into two circularly polarized components with opposite helicity. The splitting of the emission line in the magnetic field is caused by different refractive indices of the material inside the microcavity for left- and right-hand circularly polarized light, yielding two resonator modes. Thereby the emission wavelength can be fine tuned by, e.g., 2 cm−1 at 30 kG. At higher fields the laser emission is 100% circularly polarized. This indicates that lasing in this case originates from completely spin polarized carriers.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics

Nd:Ta2O5 rib waveguide lasers

Bayram Unal, Chao-Yi Tai, David P. Shepherd, James S. Wilkinson, Nicolas M. B. Perney, M. Caterina Netti, and Gregory J. Parker

Appl. Phys. Lett. 86, 021110 (2005); http://dx.doi.org/10.1063/1.1849419 (3 pages) | Cited 8 times

Online Publication Date: 5 January 2005

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Ta2O5 waveguides offer great potential for high-density active photonic crystal circuits and their combination with rare-earth dopants for active devices is of interest for increasing their potential functionality. To this end, neodymium-doped Ta2O5 rib waveguide lasers have been fabricated on an oxidized silicon wafer by rf sputtering and argon ion-beam milling and laser action in this material has been demonstrated. Lasing was observed at wavelenghts between 1060 and 1080 nm and an absorbed pump power threshold of 87 mW was obtained.
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42.60.By Design of specific laser systems
42.55.Tv Photonic crystal lasers and coherent effects
42.55.Rz Doped-insulator lasers and other solid state lasers
42.79.Gn Optical waveguides and couplers
81.15.Cd Deposition by sputtering
81.15.Jj Ion and electron beam-assisted deposition; ion plating

Synthesis and optical properties of germanium nanorod array fabricated on porous anodic alumina and Si-based templates

Y. F. Mei, Z. M. Li, R. M. Chu, Z. K. Tang, G. G. Siu, Ricky K. Y. Fu, Paul K. Chu, W. W. Wu, and K. W. Cheah

Appl. Phys. Lett. 86, 021111 (2005); http://dx.doi.org/10.1063/1.1849854 (3 pages) | Cited 16 times

Online Publication Date: 5 January 2005

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A large quantity of monocrystalline germanium nanorods and their arrays were produced on a porous anodic alumina (PAA) template utilizing saturated vapor adsorption, during which the Ge gas pressure was saturated at a high temperature in an airtight quartz tube. Raman scattering and photoluminescence (PL) results were acquired from the Ge nanorod array and discussed in details. Using Si-based PAA template with 25 nm nanopores, Si-based Ge nanorod array with a large area (larger than 1×1 cm2) was obtained and the quantum confinement effect is demonstrated in Raman spectrum.
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81.07.Bc Nanocrystalline materials
81.05.Cy Elemental semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.46.-w Structure of nanoscale materials
68.43.Mn Adsorption kinetics

Coincidence fractional Fourier transform with entangled photon pairs and incoherent light

Yangjian Cai, Qiang Lin, and Shi-Yao Zhu

Appl. Phys. Lett. 86, 021112 (2005); http://dx.doi.org/10.1063/1.1852090 (3 pages) | Cited 19 times

Online Publication Date: 5 January 2005

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The coincidence fractional Fourier transforms with entangled photon pairs and with incoherent light are introduced. Optical systems for implementing the two coincidence fractional Fourier transforms are designed. The difference between the two coincidence fractional Fourier transforms is discussed.
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42.30.Kq Fourier optics
42.50.Dv Quantum state engineering and measurements
42.25.Kb Coherence

Multifocal flat lens with left-handed metamaterial

Jeffrey D. Wilson and Zachary D. Schwartz

Appl. Phys. Lett. 86, 021113 (2005); http://dx.doi.org/10.1063/1.1850590 (3 pages) | Cited 8 times

Online Publication Date: 5 January 2005

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We show experimental results demonstrating multiple focal lengths at microwave frequencies in a flat lens constructed of left-handed metamaterial (LHM). In contrast to conventional lenses, which are constructed of materials with positive index and require a curved surface or inhomogeneous structures to focus light or other electromagnetic radiation, no curvature is needed with a LHM because of a negative effective index of refraction. Such a flat lens has the advantage of being capable of changing the focal length by simply changing the distance between the electromagnetic source and the lens.
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42.79.Bh Lenses, prisms and mirrors
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Laser bending for high-precision curvature adjustment of microcantilevers

X. Richard Zhang and Xianfan Xu

Appl. Phys. Lett. 86, 021114 (2005); http://dx.doi.org/10.1063/1.1851617 (3 pages) | Cited 9 times

Online Publication Date: 6 January 2005

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This work describes a laser based technique to adjust curvatures of silicon microcantilevers used for chemical and biological detection. In batch fabricated silicon cantilever arrays used for parallel sensing, it is often desirable that all cantilevers have nearly identical curvatures or flatness. We demonstrate that using the laser technique, it is possible to adjust curvatures by an amount as small as 3.5 μrad, for cantilevers with a typical dimension of 110×13×0.6 μm (length×width×thickness). Different laser parameters can be applied in order to achieve the required curvature adjustment. A two-dimensional finite element model of laser curvature adjustment is presented which enables the prediction of the laser processing parameters.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.62.-b Laser applications
81.40.Lm Deformation, plasticity, and creep
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
62.20.F- Deformation and plasticity
61.82.Fk Semiconductors

Laser emission from unprocessed cleavage microchip

Y. J. Chen, Y. D. Huang, X. Q. Lin, Q. G. Tan, Z. D. Luo, and Y. F. Lin

Appl. Phys. Lett. 86, 021115 (2005); http://dx.doi.org/10.1063/1.1852096 (3 pages) | Cited 6 times

Online Publication Date: 6 January 2005

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A method utilizing an unprocessed cleavage microchip as the solid-state laser gain medium is proposed. Pumped by a Ti:sapphire laser at 871 nm, 1060 nm continuous-wave laser emission with slope efficiency of 23% has been achieved in an unprocessed microchip directly obtained from a cleavage Nd3+:LaB3O6 crystal. Based on this method, it is possible to avoid the difficulty of the microchip gain medium processing and largely lower the cost of solid-state lasers.
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42.55.Rz Doped-insulator lasers and other solid state lasers
78.55.Hx Other solid inorganic materials
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Optical bistability and stationary patterns in photonic-crystal vertical-cavity surface-emitting lasers

Maurizio Dabbicco, Tommaso Maggipinto, and Massimo Brambilla

Appl. Phys. Lett. 86, 021116 (2005); http://dx.doi.org/10.1063/1.1853509 (3 pages) | Cited 4 times

Online Publication Date: 6 January 2005

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We report the experimental observation of optical bistability and coherent transverse pattern formation in optically injected, photonic-crystal vertical-cavity surface-emitting lasers, electrically biased below threshold. For injected frequency blueshifted with respect to the cavity resonance, the system exhibits optical bistability and the injected uniform plane-wave breaks up, giving rise to honeycomb- and rolls-like transverse patterns. By comparison with numerical simulations we associate the observed phenomena with the onset of a modulational instability, and discuss the application of this device as an optical memory based on the cavity soliton concept.
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42.55.Tv Photonic crystal lasers and coherent effects
42.65.Sf Dynamics of nonlinear optical systems; optical instabilities, optical chaos and complexity, and optical spatio-temporal dynamics
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Ion energy uniformity in high-frequency capacitive discharges

A. Perret, P. Chabert, J. Jolly, and J.-P. Booth

Appl. Phys. Lett. 86, 021501 (2005); http://dx.doi.org/10.1063/1.1848183 (3 pages) | Cited 20 times

Online Publication Date: 30 December 2004

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Ion energy distribution functions and ion fluxes in low-pressure, high-frequency (13.56–80 MHz) capacitive discharges were investigated both theoretically and experimentally. In most of the conditions explored, the ion energy distribution function was a single peak centered at the time-averaged plasma potential. Lower energy ions with higher fluxes are obtained as the frequency increases. The uniformity of the ion energy across large-area electrodes (40 cm2) was also studied in conditions under which the standing wave effect is important, i.e., conditions such that the rf voltage and the ion flux are strongly nonuniform. Unlike the latter quantities, the ion energy was uniform across the reactor at all frequencies, due to dc current flowing radially in the plasma and in the electrodes.
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52.25.Fi Transport properties
52.80.Pi High-frequency and RF discharges
52.65.-y Plasma simulation
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.30.-q Plasma dynamics and flow

Collective effects on the symmetric resonant charge transfer in partially ionized hydrogen plasma

Young-Dae Jung

Appl. Phys. Lett. 86, 021502 (2005); http://dx.doi.org/10.1063/1.1848178 (3 pages) | Cited 2 times

Online Publication Date: 3 January 2005

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The collective nonideal effects on the symmetric resonant charge transfer process in the intermediate velocity region are investigated in partially ionized hydrogen plasmas. The effective pseudopotential model taking into account the plasma screening and collective effects is applied to describe the interaction potential in nonideal plasmas. The electron transfer probability and cross section are obtained as functions of the energies of the symmetric and antisymmetric stationary states, nonideality plasma parameter, Debye length, and collision velocity. The results show that the collective effects enhance the symmetric resonant electron transfer probability as well as the electron transfer cross section in nonideal plasmas. It is also found that the collective effects on the symmetric resonant charge transfer process are more significant than the screening effects in nonideal plasmas.
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52.25.Fi Transport properties
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.40.Mj Particle beam interactions in plasmas
52.65.-y Plasma simulation
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Combination of time of flight direct recoiled spectroscopy and ion scattering trajectory simulations of (Ga,Mn)N growth by chemical beam epitaxy

Luz Angela Carreño and Abdelhak Bensaoula

Appl. Phys. Lett. 86, 021901 (2005); http://dx.doi.org/10.1063/1.1841478 (3 pages)

Online Publication Date: 30 December 2004

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In situ direct recoiled spectroscopy combined with scattering-recoiling trajectory simulations were applied to characterization of (Ga,Mn)N thin films grown by chemical beam epitaxy. Relative intensities of the scattering and recoiling signals recorded as a function of the sample azimuthal rotation allowed determination of the surface composition and periodicity. Models locating the Mn atoms at Ga sites and interstitial positions and the presence of N vacancies at percent levels were simulated. We find that most Mn atoms are located at Ga sites with a nonnegligible level going to interstitial positions; inclusion of N vacancies is also necessary to duplicate some experimental features. This agrees with the samples free carrier concentrations and photoluminescence measurements.
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68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.55.A- Nucleation and growth
81.05.Hd Other semiconductors
68.55.Nq Composition and phase identification
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.J- Point defects and defect clusters
68.35.Dv Composition, segregation; defects and impurities
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.S- Impurities in crystals
75.50.Pp Magnetic semiconductors

Lowered dislocation densities in uniform GaN layers grown on step-free (0001) 4H-SiC mesa surfaces

N. D. Bassim, M. E. Twigg, C. R. Eddy, J. C. Culbertson, M. A. Mastro, R. L. Henry, R. T. Holm, P. G. Neudeck, A. J. Trunek, and J. A. Powell

Appl. Phys. Lett. 86, 021902 (2005); http://dx.doi.org/10.1063/1.1849834 (3 pages) | Cited 6 times

Online Publication Date: 3 January 2005

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We report that very low threading dislocation densities (8×107/cm2) were achieved in uniform GaN layers grown by metalorganic chemical vapor deposition on (0001) 4H-SiC mesa surfaces 50 μm×50 μm in area that were completely free of steps. Transmission electron microscopy (TEM) indicated that all observable GaN film threading dislocations were of edge type. TEM analysis of the defect structure of the nucleation layer (aluminum nitride, AlN) revealed a lack of c-component dislocations, and the clean annihilation of lateral, a-type dislocations within the first 200 nm of growth, with no lateral dislocations developing threading arms. These results indicate that the elimination of steps on the initial (0001) 4H-SiC growth surface may play an important role in the removal of mixed and c-type dislocations in subsequently grown AlN and GaN heteroepitaxial layers.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Lp Transmission electron microscopy (TEM)

Effect of Cu deficiency on the defect levels of Cu0.86In1.09Se2.05 determined by spectroscopic ellipsometry

Sung-Ho Han, Falah S. Hasoon, Hamda A. Al-Thani, Allen M. Hermann, and Dean H. Levi

Appl. Phys. Lett. 86, 021903 (2005); http://dx.doi.org/10.1063/1.1849840 (3 pages) | Cited 4 times

Online Publication Date: 3 January 2005

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Room temperature spectroscopic ellipsometry measurement of Cu0.86In1.09Se2.05 reveals that shallow defect states are found in the sub-band-gap region. The energies of these defect levels are in quantitative agreement with those calculated and measured by photoluminescence, electrical conductivity, optical absorption, and deep level transient spectroscopy at low temperatures. The results can be explained in terms of the defect physics of this material and suggest that the defect levels are due to Cu deficiency. This work opens up the possibility of measuring defect levels of off-stoichiometric or heavily doped semiconductors by spectroscopic ellipsometry at room temperature.
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71.55.Ht Other nonmetals
78.66.Li Other semiconductors

Enhanced terahertz emission from porous InP (111) membranes

M. Reid, I. V. Cravetchi, R. Fedosejevs, I. M. Tiginyanu, and L. Sirbu

Appl. Phys. Lett. 86, 021904 (2005); http://dx.doi.org/10.1063/1.1849813 (3 pages) | Cited 12 times

Online Publication Date: 3 January 2005

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Bulk n-InP wafers and porous membrances with (111) crystallographic orientation have been illuminated with 120 fs pulses of 800 nm radiation from a Ti:Sapphire amplified laser system. Terahertz (THz) emission from samples was measured as a function of excitation fluence in the reflection geometry. It was established that the THz emission from both bulk and porous InP (111) saturates at high excitation fluence, emitting comparable levels of far-infrared radiation. Below saturation, however, the emission from the porous InP (111) membrane was found to be approximately an order of magnitude greater in radiated electric field or approximately two orders of magnitude in power relative to the bulk sample. The observed increase in efficiency from the porous, relative to the bulk samples, can be attributed either to the local field enhancement in the porous network for the nonlinear contribution to the radiated THz fields, or to modifications of the transient currents resulting in enhanced THz radiation.
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78.70.Gq Microwave and radio-frequency interactions
78.47.-p Spectroscopy of solid state dynamics

Structure of the carrot defect in 4H-SiC epitaxial layers

M. Benamara, X. Zhang, M. Skowronski, P. Ruterana, G. Nouet, J. J. Sumakeris, M. J. Paisley, and M. J. O’Loughlin

Appl. Phys. Lett. 86, 021905 (2005); http://dx.doi.org/10.1063/1.1849416 (3 pages) | Cited 18 times

Online Publication Date: 4 January 2005

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Transmission electron microscopy and KOH etching were used to determine the structure of the carrot defect in 4H-SiC epilayers. The defect consists of two intersecting planar faults on prismatic {1math00} and basal {0001} planes. Both faults are connected by a stair-rod dislocation with Burgers vector 1/n [10math0] with n>3 at the crossover. A Frank-partial dislocation with b = 1/12[4math03] terminates the basal fault.
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61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Formation of binary phase gratings in photopolymer-liquid crystal composites by a surface-controlled anisotropic phase separation

Jae-Hong Park, Iam Choon Khoo, Chang-Jae Yu, Min-Sik Jung, and Sin-Doo Lee

Appl. Phys. Lett. 86, 021906 (2005); http://dx.doi.org/10.1063/1.1851008 (3 pages) | Cited 8 times

Online Publication Date: 4 January 2005

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We report on formation of binary phase gratings in photopolymer-liquid crystal (PLC) composites using a surface-controlled phase separation method. The binary nature of the PLC phase gratings is produced by employing a single step photo-ablation through an amplitude photomask which precisely controls the interfacial interactions between the LC and the photopolymer on the alignment layer. A subsequent illumination of the ultraviolet light onto the whole PLC promotes an anisotropic phase separation resulting in the formation of distinct binary patterns for the PLC structure. The electrically tunable diffraction properties of the binary phase gratings are presented.
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42.70.Df Liquid crystals
42.70.Jk Polymers and organics
42.79.Dj Gratings
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
42.82.Cr Fabrication techniques; lithography, pattern transfer
61.82.Pv Polymers, organic compounds

Reversible change of birefringence sign by optical and thermal processes in an azobenzene polymethacrylate

F. J. Rodríguez, C. Sánchez, B. Villacampa, R. Alcalá, R. Cases, M. Millaruelo, and L. Oriol

Appl. Phys. Lett. 86, 021907 (2005); http://dx.doi.org/10.1063/1.1851012 (3 pages) | Cited 5 times

Online Publication Date: 4 January 2005

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Birefringence (Δn) induced in an azobenzene polymethacrylate by combination of biphotonic and thermotropic processes has subsequently been changed in sign by room temperature illumination with linearly polarized blue light. The sign of Δn can be reversed again, by simply heating up the film to 100 °C. This change of Δn between positive and negative values can be repeated several times. Besides, by appropriate choice of film thickness and blue light irradiation conditions the same absolute value for positive and negative Δn values can be obtained.
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42.70.Jk Polymers and organics
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
78.20.Fm Birefringence
61.82.Pv Polymers, organic compounds
78.66.Qn Polymers; organic compounds
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.40.Gh Other heat and thermomechanical treatments
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