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28 Nov 2011

Volume 99, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 221902 (2011); http://dx.doi.org/10.1063/1.3663578 (3 pages)

Aparna Deshpande, Kai Felix Braun, and Saw-Wai Hla
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Solar blind metal-semiconductor-metal ultraviolet photodetectors using quasi-alloy of BGaN/GaN superlattices

H. Srour, J. P. Salvestrini, A. Ahaitouf, S. Gautier, T. Moudakir, B. Assouar, M. Abarkan, S. Hamady, and A. Ougazzaden

Appl. Phys. Lett. 99, 221101 (2011); http://dx.doi.org/10.1063/1.3662974 (3 pages)

Online Publication Date: 28 November 2011

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Large internal gains that can be obtained in wide band gap semiconductors-based (GaN and ZnO types) Schottky and/or metal-semiconductor-metal photodetectors are generally accompanied by large dark current and time response. We show that, using quasi-alloy of BGaN/GaN superlattices as the active layer, the dark current can be lowered while maintaining high internal gain (up to 3 × 104) for optical power in the nW range and low time response (few tens of ns) for optical power in the W range. Furthermore, the boron incorporation allows the tuning of the cutoff wavelength.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
68.65.Cd Superlattices
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Sx Metal-semiconductor-metal structures
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Polarization dependent state to polarization independent state change in THz metamaterials

W. M. Zhu, A. Q. Liu, W. Zhang, J. F. Tao, T. Bourouina, J. H. Teng, X. H. Zhang, Q. Y. Wu, H. Tanoto, H. C. Guo, G. Q. Lo, and D. L. Kwong

Appl. Phys. Lett. 99, 221102 (2011); http://dx.doi.org/10.1063/1.3664131 (3 pages) | Cited 2 times

Online Publication Date: 28 November 2011

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We experimentally demonstrated a polarization dependent state to polarization independent state change in terahertz (THz) metamaterials. This is accomplished by reconfiguring the lattice structure of metamaterials from 2-fold to 4-fold rotational symmetry by using micromachined actuators. In experiment, it measures resonance frequency shift of 25.8% and 12.1% for TE and TM polarized incidence, respectively. Furthermore, single-band to dual-band switching is also demonstrated. Compared with the previous reported tunable metamaterials, lattice reconfiguration promises not only large tuning range but also changing of polarization dependent states, which can be used in photonic devices such as sensors, optical switches, and filters.
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42.70.-a Optical materials
42.79.Ci Filters, zone plates, and polarizers
42.65.Pc Optical bistability, multistability, and switching, including local field effects
81.20.Wk Machining, milling
07.10.Cm Micromechanical devices and systems
81.05.Xj Metamaterials for chiral, bianisotropic and other complex media

Performance enhancement of blue light-emitting diodes with a special designed AlGaN/GaN superlattice electron-blocking layer

Yun Yan Zhang and Yi An Yin

Appl. Phys. Lett. 99, 221103 (2011); http://dx.doi.org/10.1063/1.3653390 (3 pages) | Cited 6 times

Online Publication Date: 28 November 2011

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The characteristics of the nitride-based blue light-emitting diode (LED) with an AlGaN/GaN superlattice (SL) electron-blocking layer (EBL) of gradual Al mole fraction are analyzed numerically and experimentally. The emission spectra, carrier concentrations in the quantum wells, energy band diagrams, electrostatic fields, and internal quantum efficiency are investigated. The results indicate that the LED with an AlGaN/GaN SL EBL of gradual Al mole fraction has a better hole injection efficiency, lower electron leakage, and smaller electrostatic fields in its active region over the LED with a conventional rectangular AlGaN EBL or with a normal AlGaN/GaN SL EBL. The results also show that the efficiency droop is markedly improved when the SL EBL of gradual Al mole fraction is used.
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85.60.Jb Light-emitting devices

At-wavelength characterization of refractive x-ray lenses using a two-dimensional grating interferometer

Simon Rutishauser, Irene Zanette, Timm Weitkamp, Tilman Donath, and Christian David

Appl. Phys. Lett. 99, 221104 (2011); http://dx.doi.org/10.1063/1.3665063 (3 pages) | Cited 9 times

Online Publication Date: 29 November 2011

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We report on the application of a two-dimensional hard x-ray grating interferometer to x-ray optics metrology. The interferometer is sensitive to refraction angles in two perpendicular directions with a precision of 10 nrad. It is used to observe the wavefront changes induced by a single parabolic beryllium focusing lens of large radius of curvature. The lens shape is reconstructed and its residual aberrations are analyzed. Its profile differs from an ideal parabolic shape by less than 2 μm or λ/50 at λ = 0.54 Å wavelength.
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42.79.Bh Lenses, prisms and mirrors
07.85.-m X- and γ-ray instruments

GaN-based photonic crystal surface emitting lasers with central defects

Tzeng-Tsong Wu, Peng-Hsiang Weng, Yen-Ju Hou, and Tien-Chang Lu

Appl. Phys. Lett. 99, 221105 (2011); http://dx.doi.org/10.1063/1.3665251 (3 pages) | Cited 1 time

Online Publication Date: 29 November 2011

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The GaN-based photonic crystal surface emitting lasers (PCSELs) with different central defects were fabricated and investigated. The threshold energy densities increased from 3.23 to 3.51 mJ/cm2 when the central defect size increased. In addition, lasing wavelengths decreased from 400 nm to 390 nm due to the guided mode shifting phenomenon for the PCSEL cavities with larger central defects. The tendency of threshold gain and resonance wavelength for PCSELs with different central defects were calculated by the multiple scattering method and well matched to the experimental results.
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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
42.70.Qs Photonic bandgap materials

Experimental realization and modeling of a subwavelength frequency-selective plasmonic metasurface

Ping-Chun Li, Yang Zhao, Andrea Alù, and Edward T. Yu

Appl. Phys. Lett. 99, 221106 (2011); http://dx.doi.org/10.1063/1.3664634 (3 pages) | Cited 5 times

Online Publication Date: 29 November 2011

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We have modeled, fabricated, and characterized a plasmonic metasurface with subwavelength features, whose dominant resonance is the independent of incident angle and polarization, and sensitive only to the material composition and geometry of a single element. Higher-order resonances, associated with surface plasmon polariton (SPP) coupling and higher diffraction orders, are sensitive to the incident angle and the array periodicity and less pronounced compared with the metasurface resonance. Numerical simulations and theoretical analysis highlight a clear physical difference between the SPP resonances and the dominant metasurface collective resonance, whose properties may be of great interest for plasmonic solar cells and subwavelength color filters.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.86.+b Optical workshop techniques
42.79.-e Optical elements, devices, and systems

Gain assisted nanocomposite multilayers with near zero permittivity modulus at visible frequencies

Carlo Rizza, Andrea Di Falco, and Alessandro Ciattoni

Appl. Phys. Lett. 99, 221107 (2011); http://dx.doi.org/10.1063/1.3665414 (3 pages) | Cited 4 times

Online Publication Date: 30 November 2011

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We have fabricated a nano-laminate by alternating metal and gain medium layers, the gain dielectric consisting of a polymer incorporating optically pumped dye molecules. From standard reflection-transmission experiments, we show that, at a visible wavelength, both the real and the imaginary parts of the permittivity ε∥ attain very small values and we measure, at λ = 604 nm, |ε∥| = 0.04 which is 21.5% smaller than its value in the absence of optical pumping. Our investigation thus proves that a medium with a permittivity with very small modulus, a key condition promising efficient subwavelength optical steering, can be actually synthesized.
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81.16.-c Methods of micro- and nanofabrication and processing
77.22.Ch Permittivity (dielectric function)

Homeotropically aligning phase separated columnar structures for fabrication of flexible electrooptical devices

Bharat R. Acharya, Hyunchul Choi, Mohan Srinivasarao, and Satyendra Kumar

Appl. Phys. Lett. 99, 221108 (2011); http://dx.doi.org/10.1063/1.3663966 (3 pages)

Online Publication Date: 30 November 2011

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A method of achieving homeotropic alignment of liquid crystals (LCs) by ultraviolet light induced phase separation of LC from its mixture with photo-curable pre-polymer is reported. Vertical polymer columns and micro-fibrils developed during the phase separation promote homeotropic alignment of the LC director (i.e., alignment perpendicular to the LC-substrate interface), suitable for devices based on LCs possessing negative dielectric anisotropy. These vertical structures extend between two substrates and permit the fabrication of highly flexible electro-optical devices with high contrast coupled with fast response times. This simple single-step technique eliminates the need for the traditional polymer alignment layer pre-deposited on substrates.
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85.60.Pg Display systems

Up to 3 μm light emission on InP substrate using GaInAs/GaAsSb type-II quantum wells

Stephan Sprengel, Christian Grasse, Kristijonas Vizbaras, Tobias Gruendl, and Markus-Christian Amann

Appl. Phys. Lett. 99, 221109 (2011); http://dx.doi.org/10.1063/1.3665256 (3 pages) | Cited 6 times

Online Publication Date: 1 December 2011

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We present 3 μm photoluminescence at room temperature, which is achieved with GaInAs/GaAsSb type-II quantum wells on InP substrate. This long-wavelength emission became feasible by using highly compressive strained Ga0.25In0.75As and GaAs0.4Sb0.6 layers. Furthermore, a comparison between standard superlattice and so called “W” shaped quantum wells revealed that the emission linewidth can be drastically reduced by using the latter design, which is necessary for low threshold laser operation.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors

Room temperature mid-infrared surface-emitting photonic crystal laser on silicon

Binbin Weng, Jiangang Ma, Lai Wei, Lin Li, Jijun Qiu, Jian Xu, and Zhisheng Shi

Appl. Phys. Lett. 99, 221110 (2011); http://dx.doi.org/10.1063/1.3665402 (3 pages) | Cited 5 times

Online Publication Date: 1 December 2011

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We demonstrate a mid-infrared surface-emitting photonic crystal laser on silicon substrate operating at room temperature. The active region consisting of PbSe/PbSrSe multiple quantum wells was grown by molecular beam epitaxy on Si(111) substrate patterned with a photonic crystal (PC) array. The PC array forms a transverse magnetic polarized photonic bandgap at around 2840 cm−1. Under pulsed optical pumping, room temperature multimode lasing emissions were observed at wavelength ∼3.5 μm with estimated threshold peak pumping intensity of 24 kW/cm2. Angular-dependent measurement indicates the lasing is of a Gaussian-like profile with full width at half maximum of 4.66°.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.55.Tv Photonic crystal lasers and coherent effects

Continuous-wave cascaded-harmonic generation and multi-photon Raman lasing in lithium niobate whispering-gallery resonators

Jeremy Moore, Matthew Tomes, Tal Carmon, and Mona Jarrahi

Appl. Phys. Lett. 99, 221111 (2011); http://dx.doi.org/10.1063/1.3665947 (3 pages)

Online Publication Date: 1 December 2011

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We report experimental demonstration of continuous-wave cascaded-harmonic generation and Raman lasing in a millimeter-scale lithium niobate whispering-gallery resonator pumped at a telecommunication-compatible infrared wavelength. Intensity enhancement through multiple recirculations in the whispering-gallery resonator and quasi phase-matching through a nonuniform crystal poling enable simultaneous cascaded-harmonic generation up to the fourth-harmonic accompanied by stimulated Raman, two-photon, three-photon, and four-photon Raman scattering corresponding the molecular vibrational wavenumbers 632 and 255 cm−1 in z-cut lithium niobate at pump power levels as low as 200 mW. We demonstrate simultaneous cascaded-harmonic generation and Raman lasing by observing the spectrum of the scattered light from the resonator and by capturing the image of the decoupled light from the resonator on a camera.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering

Induced terahertz emission as a probe for semiconductor devices

Patrick Hoyer, Gabor Matthäus, Ulrike Blumröder, Kevin Füchsel, and Stefan Nolte

Appl. Phys. Lett. 99, 221112 (2011); http://dx.doi.org/10.1063/1.3664769 (3 pages)

Online Publication Date: 2 December 2011

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A nondestructive and contact free method for the characterization of semiconductor devices is presented using stimulated terahertz (THz) emission. For demonstration purposes, nanostructured semiconductor-insulator-semiconductor solar cells are investigated. These solar cells are based on indium tin oxide (ITO) upon black silicon (BS). During illumination with fs laser pulses, free charge carriers are generated at the junction between ITO and BS yielding the emission of broadband THz radiation. Since the THz field strength depends on the acceleration characteristics of the photoinduced charge carriers, phase sensitive detection of the emitted THz signal reflects the existing electric field distribution at the boundary zone. In contrast to existing methods where the sample is illuminated by an additional THz generator, here, the THz emission itself characterizes the sample. Moreover, only the region of THz generation is probed yielding a depth-resolved measurement setup that can be applied for the investigation of semiconductor multilayer systems in general as far as THz generation is supported.
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88.40.hj Efficiency and performance of solar cells
88.40.J- Types of solar cells
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