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2 Jul 2012

Volume 101, Issue 1, Articles (01xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 013701 (2012); http://dx.doi.org/10.1063/1.4730945 (5 pages)

Frederick Gertz, Rustam Azimov, and Alexander Khitun
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Extremely high extinction ratio terahertz broadband polarizer using bilayer subwavelength metal wire-grid structure

L. Y. Deng, J. H. Teng, L. Zhang, Q. Y. Wu, H. Liu, X. H. Zhang, and S. J. Chua

Appl. Phys. Lett. 101, 011101 (2012); http://dx.doi.org/10.1063/1.4729826 (4 pages) | Cited 2 times

Online Publication Date: 2 July 2012

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We report a broadband terahertz (THz) polarizer exhibiting extremely high polarization extinction ratio and the method to fabricate it. The polarizer consists of a bilayer subwavelength Au wire-grid structure fabricated on Si substrate by one step etching and metal formation. The THz time domain spectroscopy (THz-TDS) measurement reveals an extremely high extinction ratio of 84.9 dB at 1.67 THz, close to the detection limit of THz-TDS system, and an average extinction ratio of 69.9 dB in 0.6–3 THz frequency range. The fabricated bilayer wire-grid polarizer shows greatly enhanced performance over conventional single layer wire-grid THz polarizer.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
81.65.Cf Surface cleaning, etching, patterning

Optical tweezers with enhanced efficiency based on laser-structured substrates

D. G. Kotsifaki, M. Kandyla, I. Zergioti, M. Makropoulou, E. Chatzitheodoridis, and A. A. Serafetinides

Appl. Phys. Lett. 101, 011102 (2012); http://dx.doi.org/10.1063/1.4728992 (3 pages)

Online Publication Date: 3 July 2012

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We present an optical nanotrapping setup that exhibits enhanced efficiency, based on localized plasmonic fields around sharp metallic features. The substrates consist of laser-structured silicon wafers with quasi-ordered microspikes on the surface, coated with a thin silver layer. The resulting optical traps show orders of magnitude enhancement of the trapping force and the effective quality factor.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles

Laser ablation dynamics in metals: The thermal regime

F. P. Mezzapesa, L. L. Columbo, M. Brambilla, M. Dabbicco, A. Ancona, T. Sibillano, and G. Scamarcio

Appl. Phys. Lett. 101, 011103 (2012); http://dx.doi.org/10.1063/1.4732507 (3 pages) | Cited 2 times

Online Publication Date: 3 July 2012

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We studied the laser ablation dynamics of steel in the thermal regime both experimentally and theoretically. The real-time monitoring of the process shows that the ablation rate depends on laser energy density and ambient pressure during the exposure time. We demonstrated that the ablation efficiency can be enhanced when the pressure is reduced with respect to the atmospheric pressure for a given laser fluence, reaching an upper limit despite of high-vacuum conditions. An analytical model based on the Hertz-Knudsen law reproduces all the experimental results.
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42.62.-b Laser applications
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Eb Laser ablation

Electrical properties of GaAs photonic crystal cavity lateral p-i-n diodes

Jan Petykiewicz, Gary Shambat, Bryan Ellis, and Jelena Vučković

Appl. Phys. Lett. 101, 011104 (2012); http://dx.doi.org/10.1063/1.4732782 (5 pages) | Cited 1 time

Online Publication Date: 3 July 2012

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We investigate conduction and free-carrier injection in laterally doped GaAs p-i-n diodes formed in one and two-dimensional photonic crystal (PC) nanocavities. Finite element simulations show that the lateral geometry exhibits high conductivity for a wide range of PC parameters and allows for precise control over current flow, enabling efficient carrier injection despite fast surface recombination. Thermal simulations indicate that the temperature increase during steady-state operation is only 3.3 K in nanobeams and 0.29 K in L3 defect nanocavities. The results affirm the suitability of lateral doping in PC devices and indicate criteria for further design optimization.
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85.30.Kk Junction diodes
02.70.Dh Finite-element and Galerkin methods
42.70.Qs Photonic bandgap materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Ultrabroadband coherent electric field from far infrared to 200 THz using air plasma induced by 10 fs pulses

Eiichi Matsubara, Masaya Nagai, and Masaaki Ashida

Appl. Phys. Lett. 101, 011105 (2012); http://dx.doi.org/10.1063/1.4732524 (4 pages) | Cited 2 times

Online Publication Date: 5 July 2012

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We generated an ultrabroadband infrared pulse ranging from far infrared to 200 THz through a plasma by focusing a hollow-fiber compressed intense 10-fs pulse and its second harmonic in air. We coherently detected the signal up to 100 THz with electro-optic sampling and clarified its drastic dependence on the orientation of the second harmonic crystal in a range of 100–200 THz with an HgCdTe detector. From these, we confirmed the whole frequency components originated from the AC biased plasma and were phase locked. This result opens the possibility of a pump-probe spectroscopy which covers the whole infrared range.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques

ZnO light-emitting devices with a lifetime of 6.8 hours

J. S. Liu, C. X. Shan, H. Shen, B. H. Li, Z. Z. Zhang, L. Liu, L. G. Zhang, and D. Z. Shen

Appl. Phys. Lett. 101, 011106 (2012); http://dx.doi.org/10.1063/1.4733298 (4 pages) | Cited 2 times

Online Publication Date: 5 July 2012

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Lithium-nitrogen doped p-type Mg0.25Zn0.75O films have been realized, and p-Mg0.25Zn0.75O/n-ZnO single-heterostructured light-emitting devices (LEDs) have been constructed. Obvious emission at around 392 nm has been observed from the LEDs under the injection of continuous current, which can be attributed to the near-band-edge emission of ZnO. The LED can work continuously for 6.8 h under a continuous current of 20 mA, revealing the good reliability of the LED. The results reported in this letter reveal that reliable ZnO-based LEDs can be realized, thus high-performance ZnO-based LEDs may be promised in the future.
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85.60.Jb Light-emitting devices

Efficiency-limiting processes in Ga(NAsP)/GaP quantum well lasers

N. Hossain, S. R. Jin, S. Liebich, M. Zimprich, K. Volz, B. Kunert, W. Stolz, and S. J. Sweeney

Appl. Phys. Lett. 101, 011107 (2012); http://dx.doi.org/10.1063/1.4733312 (4 pages) | Cited 1 time

Online Publication Date: 5 July 2012

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We report on the carrier recombination mechanisms in dilute nitride Ga(NAsP)/GaP quantum well lasers. Spontaneous emission measurements show that defect-related recombination in the devices is less significant compared with other GaAs-based dilute nitride lasers. From temperature dependent measurements, we find that the threshold current density, Jth is dominated by non-radiative recombination process(es), which account for at least 91% of Jth at room temperature. The characteristic temperature, T0 (T1) is measured to be ∼104 K (∼99 K) around 200 K, which drops to ∼58 K ( ∼37 K) around room temperature. Hydrostatic pressure measurements reveal a strong increase of threshold current with increasing pressure. This implies that current leakage dominates carrier recombination which is also responsible for their low T0 and T1 values at room temperature.
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42.55.Px Semiconductor lasers; laser diodes

Fabrication and characterization of fibers with built-in liquid crystal channels and electrodes for transverse incident-light modulation

Alexander M. Stolyarov, Lei Wei, Fabien Sorin, Guillaume Lestoquoy, John D. Joannopoulos, and Yoel Fink

Appl. Phys. Lett. 101, 011108 (2012); http://dx.doi.org/10.1063/1.4733319 (4 pages) | Cited 2 times

Online Publication Date: 5 July 2012

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We report on an all-in-fiber liquid crystal (LC) structure designed for the modulation of light incident transverse to the fiber axis. A hollow cavity flanked by viscous conductors is introduced into a polymer matrix, and the structure is thermally drawn into meters of fiber containing the geometrically scaled microfluidic channel and electrodes. The channel is filled with LCs, whose director orientation is modulated by an electric field generated between the built-in electrodes. Light transmission through the LC-channel at a particular location can be tuned by the driving frequency of the applied field, which directly controls the potential profile along the fiber.
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42.79.Kr Display devices, liquid-crystal devices
42.81.Bm Fabrication, cladding, and splicing
47.61.-k Micro- and nano- scale flow phenomena
47.85.Np Fluidics
42.70.Jk Polymers and organics

Quantitative coherent scattering spectra in apertureless terahertz pulse near-field microscopes

Kiwon Moon, Youngwoong Do, Meehyun Lim, Gyuseok Lee, Hyeona Kang, Kee-Su Park, and Haewook Han

Appl. Phys. Lett. 101, 011109 (2012); http://dx.doi.org/10.1063/1.4733475 (4 pages)

Online Publication Date: 5 July 2012

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We present quantitative coherent measurements of scattering pulses and spectra in terahertz apertureless near-field microscopes. Broadband near-field image contrasts for both amplitude and phase spectra are measured directly from time-domain scattering signals with an unprecedentedly high single-scan signal-to-noise ratio (∼48 dB), with approach curves for both short (<200 nm) and long (up to 82 μm) ranges. By using the line dipole image method, we obtain quantitative broadband THz imaging contrasts with nanoscale resolution.
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07.79.Fc Near-field scanning optical microscopes
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

Stimulated Mie scattering in nanocrystals suspension

Guang S. He, Wing-Cheung Law, Liwei Liu, Xihe Zhang, and Paras N. Prasad

Appl. Phys. Lett. 101, 011110 (2012); http://dx.doi.org/10.1063/1.4730408 (4 pages) | Cited 1 time

Online Publication Date: 5 July 2012

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In this letter, we report the observation of backward stimulated Mie scattering in a suspension of CdSe/Cds/ZnS nanocrystals in chloroform, pump by 816-nm or 1064-nm nanosecond laser pulses. The observed stimulated scattering exhibits the features of no frequency-shift, low pump threshold requirement, and easy controllability. For average nanocrystals’ size of ∼5.5 nm and weight concentration of 4.5 mg/mL, the measured nonlinear reflectivity (energy conversion efficiency from pump pulse to stimulated scattering pulse) could be up to 32%. This nanoparticles-based stimulated scattering effect can find special applications for self-adapted bioimaging, high-sensitivity sensors, lasing feedback elements, and optical ranging and lidar systems.
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78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
82.70.Kj Emulsions and suspensions
78.66.Hf II-VI semiconductors
78.47.je Time resolved light scattering spectroscopy
78.47.jg Time resolved reflection spectroscopy

Numerical analysis of indirect Auger transitions in InGaN

Francesco Bertazzi, Michele Goano, and Enrico Bellotti

Appl. Phys. Lett. 101, 011111 (2012); http://dx.doi.org/10.1063/1.4733353 (4 pages) | Cited 3 times

Online Publication Date: 6 July 2012

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Indirect phonon-assisted Auger recombination mechanisms in bulk InGaN are investigated in the framework of perturbation theory, using first-principles phonon spectral density functions and electronic structures obtained by nonlocal empirical pseudopotential calculations. Nonpolar carrier-phonon interactions are treated within the rigid pseudoion framework, thus avoiding the introduction of empirical deformation potentials. The calculated indirect Auger coefficients exhibit a weak temperature dependence and dominate over direct processes for alloy compositions corresponding to the entire visible spectrum. The present results suggest that indirect Auger processes may be relevant in the operation of InGaN-based light-emitting diodes and lasers, at least in the yellow-green spectral region.
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79.20.Fv Electron impact: Auger emission
63.20.dk First-principles theory
63.20.kd Phonon-electron interactions
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Nr Semiconductor compounds
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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