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1 Dec 2008

Volume 93, Issue 22, Articles (22xxxx)

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Appl. Phys. Lett. 93, 221101 (2008); http://dx.doi.org/10.1063/1.3036234 (3 pages)

Soon Moon Jeong, Na Young Ha, Mu Guen Chee, Fumito Araoka, Ken Ishikawa, Hideo Takezoe, Suzushi Nishimura, and Goro Suzaki
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Enhanced linearly polarized lasing emission from nanoimprinted surface-emitting distributed feedback laser based on polymeric liquid crystals

Soon Moon Jeong, Na Young Ha, Mu Guen Chee, Fumito Araoka, Ken Ishikawa, Hideo Takezoe, Suzushi Nishimura, and Goro Suzaki

Appl. Phys. Lett. 93, 221101 (2008); http://dx.doi.org/10.1063/1.3036234 (3 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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The authors have demonstrated the enhancement of linearly polarized lasing emission intensity using a structure made by a simple fabrication process. The enhanced lasing is achieved using a nanoimprinted distributed feedback structure together with spin-coated polymeric liquid crystals. The backward linearly TE-polarized lasing emission is transformed to left-handed circularly polarized light (L-CPL) by employing a dye-doped polymeric nematic liquid crystal (PNLC) film as a (−1/4)λ[ = (3/4)λ] plate. The L-CPL is effectively reflected by a L-polymeric cholesteric liquid crystal film as a reflector and transformed back to TE-polarized light by the PNLC film; as a result one-directional emission intensity is enhanced.
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42.55.Mv Dye lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Ultrahigh-brightness 850 nm GaAs/AlGaAs photonic crystal laser diodes

K. Posilovic, T. Kettler, V. A. Shchukin, N. N. Ledentsov, U. W. Pohl, D. Bimberg, J. Fricke, A. Ginolas, G. Erbert, G. Tränkle, J. Jönsson, and M. Weyers

Appl. Phys. Lett. 93, 221102 (2008); http://dx.doi.org/10.1063/1.3040322 (3 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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One-dimensional photonic crystal lasers emitting in the 850 nm range show high internal quantum efficiencies of 93% and very narrow vertical beam divergence of 7.1° (full width at half maximum). 50 μm broad area lasers with unpassivated facets exhibit a high total output power of nearly 20 W in pulsed mode with a divergence of 9.5°×11.3° leading to a record brightness of 3×108 W cm−2 sr−1, being presently the best value ever reported for a single broad area laser diode. 100 μm broad devices with unpassivated facets show continuous wave operation with an output power of 1.9 W.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Tv Photonic crystal lasers and coherent effects
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.70.Qs Photonic bandgap materials

Twisted liquid crystal pi cell stabilized by polymer-sustained alignment

Tien-Jung Chen, Yuan-Hsin Cheng, and Sheng-Ming Wu

Appl. Phys. Lett. 93, 221103 (2008); http://dx.doi.org/10.1063/1.3040325 (3 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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A uniform π-twist liquid crystal (LC) alignment was stabilized in a pi cell by photopolymerization of a minute amount of monomers without using any chiral material. Controlling UV exposure time can vary the LC pretilt angle to achieve a stabilized π-twist state. This type of π-twisted LC cell made using the polymer-sustained alignment has a pretilt angle estimated to be ∼ 20°. This cell can quickly transform into a bend state at a low driving voltage and shows excellent brightness and optical contrast, as compared with a conventional pi cell and a chiral-doped cell.
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42.79.Kr Display devices, liquid-crystal devices
82.35.-x Polymers: properties; reactions; polymerization
82.50.-m Photochemistry
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures

GaN nanostructured p-i-n photodiodes

J. L. Pau, C. Bayram, P. Giedraitis, R. McClintock, and M. Razeghi

Appl. Phys. Lett. 93, 221104 (2008); http://dx.doi.org/10.1063/1.3041641 (3 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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We report the fabrication of nanostructured p-i-n photodiodes based on GaN. Each device comprises arrays of ∼ 200 nm diameter and 520 nm tall nanopillars on a 1 μm period, fabricated by e-beam lithography. Strong rectifying behavior was obtained with an average reverse current per nanopillar of 5 fA at −5 V. In contrast to conventional GaN diodes, nanostructured devices reproducibly show ideality factors lower than 2. Enhanced tunneling through sidewall surface states is proposed as the responsible mechanism for this behavior. Under backillumination, the quantum efficiency in nanostructured devices is partly limited by the collection efficiency of holes into the nanopillars.
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85.60.Dw Photodiodes; phototransistors; photoresistors
81.16.Nd Micro- and nanolithography

Demonstration of enhanced absorption in thin film Si solar cells with textured photonic crystal back reflector

L. Zeng, P. Bermel, Y. Yi, B. A. Alamariu, K. A. Broderick, J. Liu, C. Hong, X. Duan, J. Joannopoulos, and L. C. Kimerling

Appl. Phys. Lett. 93, 221105 (2008); http://dx.doi.org/10.1063/1.3039787 (3 pages) | Cited 49 times

Online Publication Date: 1 December 2008

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Herein the authors report the experimental application of a powerful light trapping scheme, the textured photonic crystal (TPC) backside reflector, to thin film Si solar cells. TPC combines a one-dimensional photonic crystal as a distributed Bragg reflector with a diffraction grating. Light absorption is strongly enhanced by high reflectivity and large angle diffraction, as designed with scattering matrix analysis. 5 μm thick monocrystalline thin film Si solar cells integrated with TPC were fabricated through an active layer transfer technique. Measured short circuit current density Jsc was increased by 19%, compared to a theoretical prediction of 28%.
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84.60.Jt Photoelectric conversion
42.70.Qs Photonic bandgap materials
42.79.Dj Gratings

Midinfrared quantum cascade detector with a spectrally broad response

Daniel Hofstetter, Fabrizio R. Giorgetta, Esther Baumann, Quankui Yang, Christian Manz, and Klaus Köhler

Appl. Phys. Lett. 93, 221106 (2008); http://dx.doi.org/10.1063/1.3036897 (3 pages) | Cited 9 times

Online Publication Date: 3 December 2008

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A midinfrared quantum cascade detector with a spectrally broad (ΔE/E = 27.3%) response is designed, fabricated, and tested. This detector consists of 26 differently designed active region stages in order to cover a wavelength region from 4.7 to 7.4 μm. The device could be operated above room temperature and showed peak responsivities of 13 mA/W at 10 K and 1.25 mA/W at room temperature. A background limited detectivity of 1.55×1010 Jones was seen up to a temperature TBLIP of 110 K.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.15.Eq Optical system design
42.86.+b Optical workshop techniques
42.87.-d Optical testing techniques
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

An inverted organic solar cell employing a sol-gel derived ZnO electron selective layer and thermal evaporated MoO3 hole selective layer

A. K. K. Kyaw, X. W. Sun, C. Y. Jiang, G. Q. Lo, D. W. Zhao, and D. L. Kwong

Appl. Phys. Lett. 93, 221107 (2008); http://dx.doi.org/10.1063/1.3039076 (3 pages) | Cited 122 times

Online Publication Date: 3 December 2008

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We reported an efficient inverted bulk-heterojunction [regioregular of poly(3-hexylthiophene): (6,6)-phenyl C61 butyric acid methyl ester] solar cell with a highly transparent sol-gel derived ZnO film as electron selective layer and MoO3 as hole selective layer. By modifying the precursor concentration of sol from 0.75 to 0.1M, the optical transmittance of ZnO film increases from 75% to 95%. This improvement in transmittance increases the short-circuit density of inverted solar cell from 5.986 to 8.858 mA/cm2 without sacrificing the open-circuit voltage and fill factor of the device. We also demonstrated that the device incorporated with MoO3 has a larger open-circuit voltage and fill factor than the device without MoO3. Power conversion efficiency of 3.09% was achieved under simulated AM 1.5G illumination of 100 mW/cm2.
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84.60.Jt Photoelectric conversion

Microstructural and optical analysis of superresolution phenomena due to Ge2Sb2Te5 thin films at blue light regime

Hyun Seok Lee, Taek Sung Lee, Yongwoon Lee, Jooho Kim, Suyoun Lee, Joo-Youl Huh, Donghwan Kim, and Byung-ki Cheong

Appl. Phys. Lett. 93, 221108 (2008); http://dx.doi.org/10.1063/1.3040695 (3 pages) | Cited 3 times

Online Publication Date: 3 December 2008

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Superresolution (SR) phenomena due to Ge2Sb2Te5 films were examined by combined analysis of the transmission electron microscopy (TEM) microstructures of the laser-irradiated films and the results from dynamic and static tests using blue lasers. A new finding was made that comprises a complementary case of the classical SR readout by Ge2Sb2Te5 film; an amorphous band instead of a closed aperture of melt in the crystalline background forms behind a moving laser but still produces a high SR signal. A complete carrier-to-noise-ratio curve of a SR-read-only memory employing Ge2Sb2Te5 may be derived from a nonlinear optical effect, specifically thermally assisted saturable absorption.
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68.55.-a Thin film structure and morphology
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
78.66.-w Optical properties of specific thin films

Optical hyperspace for plasmons: Dyakonov states in metamaterials

Zubin Jacob and Evgenii E. Narimanov

Appl. Phys. Lett. 93, 221109 (2008); http://dx.doi.org/10.1063/1.3037208 (3 pages) | Cited 10 times

Online Publication Date: 4 December 2008

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We show that the subdiffraction imaging behavior observed in the magnifying superlens experiment, [ Smolyaninov et al., Science 317, 1699 (2007) ] is due to the hyperbolic dispersion of Dyakonov plasmons supported by the device. These states which are a special case of Dyakonov surface waves [ Dyakonov, Sov. Phys. JETP 67, 714 (1988) ] exist at the interface of a metal and an anisotropic dielectric giving rise to plasmon beams on resonance. Furthermore, we describe how the unique properties of metamaterial Dyakonov plasmons can be tailored for plasmonic devices.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Continuous optoelectrowetting for picoliter droplet manipulation

P. Y. Chiou, Sung-Yong Park, and Ming C. Wu

Appl. Phys. Lett. 93, 221110 (2008); http://dx.doi.org/10.1063/1.3039070 (3 pages) | Cited 14 times

Online Publication Date: 4 December 2008

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We report on a continuous optoelectrowetting mechanism enabling continuous high spatial resolution optical modulation of electrowetting effect on a featureless planar photoconductive amorphous silicon surface. Dynamically patterned “virtual electrode” switches voltage between the amorphous silicon layer and the dielectric layer for contact angle modulation. This device is particularly attractive for manipulating picoliter droplets. We have experimentally demonstrated trapping and moving of 10 and 50 pl droplets at a speed of 1 mm/s using a light beam.
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68.08.Bc Wetting
72.40.+w Photoconduction and photovoltaic effects
68.03.Cd Surface tension and related phenomena
81.16.Ta Atom manipulation
77.55.-g Dielectric thin films

Elimination of total internal reflection in GaInN light-emitting diodes by graded-refractive-index micropillars

Jong Kyu Kim, Ahmed N. Noemaun, Frank W. Mont, David Meyaard, E. Fred Schubert, David J. Poxson, Hyunsoo Kim, Cheolsoo Sone, and Yongjo Park

Appl. Phys. Lett. 93, 221111 (2008); http://dx.doi.org/10.1063/1.3041644 (3 pages) | Cited 16 times

Online Publication Date: 4 December 2008

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A method for enhancing the light-extraction efficiency of GaInN light-emitting diodes (LEDs) by complete elimination of total internal reflection is reported. Analytical calculations show that GaInN LEDs with multilayer graded-refractive-index pillars, in which the thickness and refractive index of each layer are optimized, have no total internal reflection. This results in a remarkable improvement in light-extraction efficiency. GaInN LEDs with five-layer graded-refractive-index pillars, fabricated by cosputtering TiO2 and SiO2, show a light-output power enhanced by 73% and a strong side emission, consistent with analytical calculations and ray-tracing simulations.
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85.60.Jb Light-emitting devices
85.60.Bt Optoelectronic device characterization, design, and modeling
81.15.Cd Deposition by sputtering
68.65.Ac Multilayers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

All-optical routing by light storage in a Pr3+:Y2SiO5 crystal

Hai-Hua Wang, Ai-Jun Li, Dun-Mao Du, Yun-Fei Fan, Lei Wang, Zhi-Hui Kang, Yun Jiang, Jin-Hui Wu, and Jin-Yue Gao

Appl. Phys. Lett. 93, 221112 (2008); http://dx.doi.org/10.1063/1.3041645 (3 pages) | Cited 9 times

Online Publication Date: 5 December 2008

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We experimentally demonstrate an all-optical routing based on light storage in a Pr3+:Y2SiO5 crystal. Under electromagnetically induced transparency, the optical information of the probe light pulse can be stored in the crystal. By simultaneously switching on two retrieve control fields in the release process, the stored optical information from one light channel can be distributed into two light channels. Such an all-optical routing in solids may have practical applications in quantum information and all-optical network.
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42.79.Vb Optical storage systems, optical disks
42.70.Mp Nonlinear optical crystals
03.67.Hk Quantum communication
42.81.Uv Fiber networks
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption

Terahertz emission from silicon and magnesium doped indium nitride

Ingrid Wilke, Ricardo Ascazubi, Hai Lu, and William J. Schaff

Appl. Phys. Lett. 93, 221113 (2008); http://dx.doi.org/10.1063/1.3043450 (3 pages) | Cited 12 times

Online Publication Date: 5 December 2008

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We report an experimental study of femtosecond optically excited emission of terahertz frequency electromagnetic radiation from as-grown n-type InN, silicon doped InN, and magnesium doped InN. We have measured the terahertz emission from these materials as function of dc Hall mobility and carrier concentrations. Terahertz emission from InN:Si and native n-type InN increases with mobility as expected for transient photocurrents as primary mechanism of terahertz emission from InN. InN:Mg exhibits enhanced terahertz emission compared to InN:Si. This is experimental evidence for Mg being electrically active as an acceptor in InN. Terahertz emission from InN:Si is less strong than terahertz emission from native n-type InN because of an increased electron concentration due to silicon being an electrically active donor in InN.
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78.47.J- Ultrafast spectroscopy (<1 psec)

Cone-beam tomography of propagation-based imaging

T. T. Li, H. Li, and L. H. Diao

Appl. Phys. Lett. 93, 221114 (2008); http://dx.doi.org/10.1063/1.3043452 (3 pages)

Online Publication Date: 5 December 2008

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A tomography algorithm is proposed for the reconstruction of the three-dimensional (3D) distribution of the real refractive index of a pure phase sample from the projections of cone-beam propagation-based imaging (PBI). The algorithm first retrieves the integral of the real refractive index based on the formula described in this letter, and then a conventional computed tomography algorithm is performed to reconstruct the 3D distribution of the real refractive index of the sample. The computer simulations show that this method is effective for PBI tomography.
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42.30.Wb Image reconstruction; tomography
42.25.Bs Wave propagation, transmission and absorption
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