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9 Feb 2009

Volume 94, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 062105 (2009); http://dx.doi.org/10.1063/1.3079078 (3 pages)

Ikai Lo, Chia-Ho Hsieh, Yu-Chi Hsu, Wen-Yuan Pang, and Ming-Chi Chou
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Room temperature midinfrared electroluminescence from InAs quantum dots

D. Wasserman, T. Ribaudo, S. A. Lyon, S. K. Lyo, and E. A. Shaner

Appl. Phys. Lett. 94, 061101 (2009); http://dx.doi.org/10.1063/1.3080688 (3 pages) | Cited 5 times

Online Publication Date: 9 February 2009

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We demonstrate room temperature midinfrared electroluminescence from intersublevel transitions in self-assembled InAs quantum dots. The dots are grown in GaAs/AlGaAs heterostructures designed to maximize current injection into dot excited states while preferentially removing electrons from the ground states. As such, these devices resemble quantum cascade lasers. However, rigorous modeling of carrier transport through the devices indicates that the current transport mechanism for quantum dot active regions differs from that of quantum-well-based midinfrared lasers. We present the calculated energy states and transport mechanism for an intersublevel quantum dot emitter, as well as experimental electroluminescence data for these structures.
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78.67.Hc Quantum dots
73.63.Kv Quantum dots
73.21.La Quantum dots
78.60.Fi Electroluminescence
81.07.Ta Quantum dots

Multimode laser emission from laterally confined organic microcavities

M. Sudzius, M. Langner, S. I. Hintschich, V. G. Lyssenko, H. Fröb, and K. Leo

Appl. Phys. Lett. 94, 061102 (2009); http://dx.doi.org/10.1063/1.3080689 (3 pages) | Cited 3 times

Online Publication Date: 9 February 2009

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Room-temperature multimode laser emission is observed in a microcavity consisting of dielectric mirrors and small-molecular-weight organic photonic dots as a cavity layer. The structure shows simultaneous lasing of a wide variety of transverse modes. A comparison of the laser operating characteristics with those of unpatterned structures shows an enhancement in the spontaneous emission coupling factor by more than two orders of magnitude due to the lateral confinement. The spectral features are in quantitative agreement with calculations of quantized photonic states in three-dimensional optical cavities.
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42.55.Sa Microcavity and microdisk lasers
42.55.Px Semiconductor lasers; laser diodes

Large vacuum Rabi splitting in ZnO-based hybrid microcavities observed at room temperature

Jun-Rong Chen, Tien-Chang Lu, Yung-Chi Wu, Shiang-Chi Lin, Wei-Rein Liu, Wen-Feng Hsieh, Chien-Cheng Kuo, and Cheng-Chung Lee

Appl. Phys. Lett. 94, 061103 (2009); http://dx.doi.org/10.1063/1.3079398 (3 pages) | Cited 13 times

Online Publication Date: 9 February 2009

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Wide-band gap ZnO semiconductors are attractive materials for the investigation of microcavity exciton polaritons due to the large exciton binding energy and oscillator strength. We report the growth and characterization of bulk ZnO-based hybrid microcavity. The phenomenon of strong exciton-photon coupling at room temperature has been observed in the ZnO-based hybrid microcavity structure, which consists of 30 pair epitaxially grown AlN/AlGaN distributed Bragg reflector (DBR) on the bottom side of the 3/2λ thick ZnO cavity and 9 pair SiO2/HfO2 DBR as the top mirror. The cavity quality factor is about 221. The experimental results show good agreement with theoretically calculated exciton-polariton dispersion curves based on transfer matrix method. From the theoretical and experimental exciton-polariton dispersion curves with two different cavity-exciton detuning values, the large vacuum Rabi splitting is estimated to be about 58 meV in the ZnO-based hybrid microcavity.
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42.82.-m Integrated optics
71.15.Nc Total energy and cohesive energy calculations
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
71.35.-y Excitons and related phenomena
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Mode locking of a GaInN semiconductor laser with an internal saturable absorber

Masahiro Yoshita, Masaru Kuramoto, Masao Ikeda, and Hiroyuki Yokoyama

Appl. Phys. Lett. 94, 061104 (2009); http://dx.doi.org/10.1063/1.3079403 (3 pages) | Cited 7 times

Online Publication Date: 9 February 2009

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We demonstrated the mode locking of an external-cavity 404 nm GaInN semiconductor laser diode with an internal saturable absorber layer for the first time. Stable passive mode locking was confirmed at a repetition rate of 840 MHz. Furthermore, hybrid mode-locking operation incorporating rf current modulation generated optical pulses of 20 ps duration and 0.4 W peak power.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Structural tuning of color chromaticity through nonradiative energy transfer by interspacing CdTe nanocrystal monolayers

Neslihan Cicek, Sedat Nizamoglu, Tuncay Ozel, Evren Mutlugun, Durmus Ugur Karatay, Vladimir Lesnyak, Tobias Otto, Nikolai Gaponik, Alexander Eychmüller, and Hilmi Volkan Demir

Appl. Phys. Lett. 94, 061105 (2009); http://dx.doi.org/10.1063/1.3079679 (3 pages) | Cited 14 times

Online Publication Date: 9 February 2009

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We proposed and demonstrated architectural tuning of color chromaticity by controlling photoluminescence decay kinetics through nonradiative Förster resonance energy transfer in the heterostructure of layer-by-layer spaced CdTe nanocrystal (NC) solids. We achieved highly sensitive tuning by precisely adjusting the energy transfer efficiency from donor NCs to acceptor NCs via controlling interspacing between them at the nanoscale. By modifying decay lifetimes of donors from 12.05 to 2.96 ns and acceptors from 3.68 to 14.57 ns, we fine-tuned chromaticity coordinates from (x,y) = (0.575,0.424) to (0.632, 0.367). This structural adjustment enabled a postsynthesis color tuning capability, alternative or additive to using the size, shape, and composition of NCs.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Microscopic analysis of mid-infrared type-II “W” diode lasers

J. Hader, J. V. Moloney, S. W. Koch, I. Vurgaftman, and J. R. Meyer

Appl. Phys. Lett. 94, 061106 (2009); http://dx.doi.org/10.1063/1.3080216 (3 pages) | Cited 5 times

Online Publication Date: 9 February 2009

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Mid-infrared diode lasers with type-II “W” active regions are analyzed using a fully microscopic many-body theory. The Auger carrier losses are found to dominate over radiative losses even at low temperatures. The experimentally observed strong temperature-dependent increase in Auger losses is shown to be a consequence of thermal gain reduction causing increased threshold carrier densities. Good agreement between theory and experiment is demonstrated for temperature-dependent photoluminescence spectra as well as threshold loss currents.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Focusing and spectral enhancement of a repetition-rated, laser-driven, divergent multi-MeV proton beam using permanent quadrupole magnets

M. Nishiuchi, I. Daito, M. Ikegami, H. Daido, M. Mori, S. Orimo, K. Ogura, A. Sagisaka, A. Yogo, A. S. Pirozhkov, H. Sugiyama, H. Kiriyama, H. Okada, S. Kanazawa, S. Kondo, et al.

Appl. Phys. Lett. 94, 061107 (2009); http://dx.doi.org/10.1063/1.3078291 (3 pages) | Cited 13 times

Online Publication Date: 9 February 2009

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A pair of conventional permanent magnet quadrupoles is used to focus a 2.4 MeV laser-driven proton beam at a 1 Hz repetition rate. The magnetic field strengths are 55 and 60 T/m for the first and second quadrupoles, respectively. The proton beam is focused to a spot with a size of less than ∼ 3×8 mm2 at a distance of 650 mm from the source. This result is in good agreement with the Monte Carlo particle trajectory simulation.
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29.27.Eg Beam handling; beam transport
52.38.Kd Laser-plasma acceleration of electrons and ions
52.65.Pp Monte Carlo methods
29.25.Ni Ion sources: positive and negative
41.75.Ak Positive-ion beams

Oscillatory variations in the Q factors of high quality micropillar cavities

S. Reitzenstein, N. Gregersen, C. Kistner, M. Strauss, C. Schneider, L. Pan, T. R. Nielsen, S. Höfling, J. Mørk, and A. Forchel

Appl. Phys. Lett. 94, 061108 (2009); http://dx.doi.org/10.1063/1.3081030 (3 pages) | Cited 3 times

Online Publication Date: 10 February 2009

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We report on the observation of oscillatory variations in the quality (Q) factor of quantum dot-micropillar cavities based on planar Bragg reflectors. The oscillatory behavior in the Q versus diameter dependence appears in the diameter range between 1.0 and 4.0 μm, has a characteristic period of a few hundred nanometers and increases in amplitude with increasing reflectivity of the planar microcavity structures. The experimental results are well reproduced by numerical calculations which support the interpretation that the Q oscillations are caused by coupling of propagating Bloch modes of different orders at the mirror interfaces.
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42.82.-m Integrated optics
42.79.Dj Gratings
42.79.Gn Optical waveguides and couplers

Near-IR subwavelength microdisk lasers

Q. Song, H. Cao, S. T. Ho, and G. S. Solomon

Appl. Phys. Lett. 94, 061109 (2009); http://dx.doi.org/10.1063/1.3081106 (3 pages) | Cited 26 times

Online Publication Date: 10 February 2009

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We report single-mode lasing in subwavelength GaAs disks under optical pumping. The disks are fabricated by standard photolithography and two steps of wet chemical etching. The simple fabrication method can produce submicron disks with good circularity, smooth boundary, and vertical sidewalls. The smallest lasing disks have a diameter of 627 nm and thickness of 265 nm. The ratio of the disk diameter to the vacuum lasing wavelength is about 0.7. Our numerical simulations confirm that the lasing modes are whispering-gallery modes with the azimuthal number as small as 4 and a modal volume of 0.97(λ/n)3.
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42.55.Sa Microcavity and microdisk lasers
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.60.Fc Modulation, tuning, and mode locking

Bidirectional direct-current electroluminescence from i-MgxZn1−xO/n-ZnO/SiOx double-barrier heterostructures on Si

Peiliang Chen, Xiangyang Ma, Dongsheng Li, Yuanyuan Zhang, and Deren Yang

Appl. Phys. Lett. 94, 061110 (2009); http://dx.doi.org/10.1063/1.3081109 (3 pages) | Cited 7 times

Online Publication Date: 10 February 2009

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We report bidirectional direct-current electroluminescence (EL) from i-MgxZn1−xO/n-ZnO/SiOx double-barrier heterostructures on Si. When the heterostructure-based device is forward biased with negative voltage applied on Si, ultraviolet (UV) emission is more intense than visible emissions. The visible emissions appear only at sufficiently high currents. As the device is reverse biased, the visible emissions dominate the EL at low currents. However, they are gradually overridden by the UV emission with increasing current. The EL mechanism has been discussed in terms of energy band structures of the device under forward and reverse biases.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors

Liquid crystal dynamic flow control by bidirectional alignment surface

Y. W. Li, C. Y. Lee, and H. S. Kwok

Appl. Phys. Lett. 94, 061111 (2009); http://dx.doi.org/10.1063/1.3080198 (3 pages) | Cited 2 times

Online Publication Date: 10 February 2009

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We investigate the behavior of liquid crystal dynamic flow in a cell with a bidirectional alignment (BDA) surface. Numerical simulations show that with a BDA surface having a pitch comparable to the cell gap d, the liquid crystal dynamic flow direction can be controlled by the driving voltage. Such an effect can be applied to bistable twisted nematic displays without the need for anchoring breaking.
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47.57.Lj Flows of liquid crystals
61.30.-v Liquid crystals

Giant birefringence and tunable differential group delay in Bragg reflector based on tapered three-dimensional hollow waveguide

Mukesh Kumar, Takahiro Sakagichi, and Fumio Koyama

Appl. Phys. Lett. 94, 061112 (2009); http://dx.doi.org/10.1063/1.3075058 (3 pages) | Cited 6 times

Online Publication Date: 10 February 2009

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A tunable Bragg reflector based on a tapered three-dimensional (3D) hollow waveguide (HWG) with variable taper angle has been proposed and demonstrated. A large grating coupling coefficient for a large reflection band and a giant birefringence of 0.01 have been achieved by optimizing the structure of the 3D HWG. The large birefringence causes a delay difference between the orthogonal polarizations and the variable taper angle provides tuning in the delay difference. A 13 ps tuning in differential group delay has been reported with a 3 mm long compact device, which can be used for adjustable compensation of polarization mode dispersion in optical fiber links.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.79.Dj Gratings
42.82.-m Integrated optics
42.82.Et Waveguides, couplers, and arrays

Noncontact and nondestructive identification of neural circuits with a femtosecond laser

Xiuli Liu, Xiaohua Lv, Shaoqun Zeng, Wei Zhou, and Qingming Luo

Appl. Phys. Lett. 94, 061113 (2009); http://dx.doi.org/10.1063/1.3080218 (3 pages) | Cited 6 times

Online Publication Date: 10 February 2009

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Identifying neuronal connections is regarded as essential in understanding the structure and functions of neural circuits. However, the issue is difficult to resolve. Due to its ultrahigh peak power, the femtosecond laser was used to stimulate neuron circuits in this study. Our results showed that optical stimulation of one neuron triggered significant calcium responses in the neighboring neurons. According to the responses, neural connections were estimated and the functional topology of the neural circuit was mapped. The optical identification of neural connections proved to be noncontact, nondestructive, and highly reproducible, which would enable characterizing the dynamics of neural circuits.
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87.85.D- Applied neuroscience
87.19.L- Neuroscience
87.63.-d Non-ionizing radiation equipment and techniques
87.16.dp Transport, including channels, pores, and lateral diffusion

Narrow-band metal-oxide-semiconductor photodetector

W. S. Ho, C.-H. Lin, T.-H. Cheng, W. W. Hsu, Y.-Y. Chen, P.-S. Kuo, and C. W. Liu

Appl. Phys. Lett. 94, 061114 (2009); http://dx.doi.org/10.1063/1.3077313 (3 pages) | Cited 1 time

Online Publication Date: 11 February 2009

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Si-based photodetectors for narrow-band ultraviolet light (319 nm) and green light (500 nm) detection are demonstrated using a metal-oxide-semiconductor tunneling structure. By using appropriate selection of gate metal, the metal-oxide-semiconductor tunneling diode can detect specific range of light. Due to the spectral dependence of absorption and reflection of the Ag and Au as gate electrodes, the narrow-band detection of ultraviolet and green light can be achieved, respectively. The photodetectors with 130 nm thick Ag gate and 70 nm thick Au gate exhibit peak responsivities of 5.1 and 0.3 mA/W at 319 and 500 nm, respectively.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Electroluminescence from TiO2/p+-Si heterostructure

Yuanyuan Zhang, Xiangyang Ma, Peiliang Chen, Dongsheng Li, and Deren Yang

Appl. Phys. Lett. 94, 061115 (2009); http://dx.doi.org/10.1063/1.3078409 (3 pages) | Cited 6 times

Online Publication Date: 12 February 2009

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Titanium films sputtered on heavily boron-doped (p+) silicon substrates were thermally oxidized to form electroluminescent TiO2/p+-Si heterostructures. The electroluminescence (EL) features a broad spectrum covering red, green, and blue regions. We believe that in TiO2 recombinations between electrons at oxygen-vacancy-related energy levels and holes in the valence band result in the EL. Furthermore, the EL mechanism has been explained in terms of the energy band diagram of the TiO2/p+-Si heterostructure, which possesses an intermediate ultrathin SiOx layer revealed by high resolution transmission microscopy.
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78.66.Li Other semiconductors
68.55.ag Semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.60.Fi Electroluminescence
61.72.jd Vacancies
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Measurement of electron overflow in 450 nm InGaN light-emitting diode structures

Kenneth J. Vampola, Michael Iza, Stacia Keller, Steven P. DenBaars, and Shuji Nakamura

Appl. Phys. Lett. 94, 061116 (2009); http://dx.doi.org/10.1063/1.3081059 (3 pages) | Cited 39 times

Online Publication Date: 12 February 2009

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Test structures were developed to experimentally measure the presence of electron overflow in light-emitting diodes (LEDs) under typical bias conditions. These test structures are comprised of a standard LED structure with an extra Mg-doped quantum well inserted on the p-type side of the electron blocking layer. Electrons escaping the active region recombine in the extra quantum well and the corresponding photon emission is observed. No electron overflow was observed at low current densities. At intermediate current densities where efficiency droop occurs, overflow was observed and increased with increasing current density. The onset of electron overflow occurred at slightly lower current densities than the onset of efficiency droop. Auger-assisted overflow, a by-product of the Auger process, is considered in addition to traditional overflow mechanisms.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

AlN/AlGaN short-period superlattice sacrificial layers in laser lift-off for vertical-type AlGaN-based deep ultraviolet light emitting diodes

Misaichi Takeuchi, Tomohiro Maegawa, Hiroshi Shimizu, Shin Ooishi, Takumi Ohtsuka, and Yoshinobu Aoyagi

Appl. Phys. Lett. 94, 061117 (2009); http://dx.doi.org/10.1063/1.3081060 (3 pages) | Cited 3 times

Online Publication Date: 12 February 2009

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Large-area ( ∼ 1 cm2) laser lift-off (LLO) wafer separation of Al0.45Ga0.55N layers from AlN/sapphire templates has been demonstrated by using 200-period AlN/Al0.22Ga0.78N short-period superlattice (SPSL) sacrificial layers instead of conventional GaN photoabsorbing layers. The SPSL functions as the photoabsorbing and mechanically weakened layer in the LLO process. This SPSL-assisted LLO technique promises future progress of vertical-type deep ultraviolet light emitting diodes and freestanding AlN–AlGaN bulk substrates.
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85.60.Jb Light-emitting devices

The substrate thickness dependence of the photovoltage in LaAlO3−δ/Si heterostructures

Juan Wen, Kui-juan Jin, Meng He, Huibin Lu, Fang Yang, and Guozhen Yang

Appl. Phys. Lett. 94, 061118 (2009); http://dx.doi.org/10.1063/1.3081400 (3 pages) | Cited 3 times

Online Publication Date: 12 February 2009

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The photoelectric properties of LaAlO3−δ/Si heterostructures with different substrate thicknesses were systematically investigated, in which the LaAlO3−δ thin films were epitaxially grown on p-type Si substrates by a computer-controlled laser molecular-beam epitaxy system. Picosecond photoelectric response was observed, and the photoelectric sensitivity was improved greatly by decreasing the thickness of the Si substrates. The maximum photoelectric sensitivity reached 85.6 V/W, and faster photoelectric response was obtained with thinner Si substrate. The experimental results demonstrate that the photoelectrical effects on heterostructures consisting of perovskite oxide and thin silicon substrate are not only with fast response but also with high sensitivity.
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72.40.+w Photoconduction and photovoltaic effects
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Velocity-matched terahertz generation by optical rectification in an organic nonlinear optical crystal using a Ti:sapphire laser

Fabian D. J. Brunner, Arno Schneider, and Peter Günter

Appl. Phys. Lett. 94, 061119 (2009); http://dx.doi.org/10.1063/1.3080214 (3 pages) | Cited 4 times

Online Publication Date: 12 February 2009

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Broadband terahertz pulses have been generated in 2-cyclooctylamino-5-nitropyridine (COANP) single crystals by optical rectification of 150 fs laser pulses from an amplified Ti:sapphire laser operating at 776 nm. Due to better velocity-matching and a higher figure of merit, COANP allows more efficient terahertz generation between 0.2 and 2.4 THz than the benchmark electro-optic crystal ZnTe at this laser wavelength. The peak amplitude of the terahertz signal obtained in COANP was 2.5 times larger in the time-domain and 2.1 times larger in the frequency-domain compared to ZnTe. We achieved a 4.3 times higher energy conversion efficiency in COANP than in ZnTe.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Jk Polymers and organics
42.70.Mp Nonlinear optical crystals
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Analysis of optical gain property in the InGaN/GaN triangular shaped quantum well under the piezoelectric field

Ziwen Yang, Rui Li, Qiyuan Wei, Tao Yu, Yanzhao Zhang, Weihua Chen, and Xiaodong Hu

Appl. Phys. Lett. 94, 061120 (2009); http://dx.doi.org/10.1063/1.3075862 (3 pages) | Cited 12 times

Online Publication Date: 12 February 2009

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InGaN/GaN triangular quantum wells (QWs) are investigated theoretically, and the electron-hole wave-function overlap and optical gain characteristics are analyzed. The strong internal piezoelectric field is taken into account to explain the major difference between the optical properties of triangular QWs and conventional rectangular QWs. Our calculations reveal that triangular QWs, in comparison to rectangular QWs, provide higher electron-hole wave-function overlap and are less affected by the quantum confined Stark effect. Furthermore, triangular QWs exhibit increased optical gain and higher polarization degree, which are beneficial to GaN-based light emitting devices.
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78.67.De Quantum wells
78.20.Jq Electro-optical effects

Experimental two-dimensional field mapping of total internal reflection lateral beam shift in a self-collimated photonic crystal

J. L. Garcia-Pomar, J. N. Gollub, J. J. Mock, D. R. Smith, and M. Nieto-Vesperinas

Appl. Phys. Lett. 94, 061121 (2009); http://dx.doi.org/10.1063/1.3085768 (3 pages) | Cited 1 time

Online Publication Date: 13 February 2009

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A lateral beam shift is demonstrated both theoretically and in microwave experiments when total internal reflection takes place at the boundary of a self-collimating two-dimensional photonic crystal consisting of an array of high index dielectric cylinders. We further show the dependence of this shift on the cut of the last row of cylinders that defines the crystal interface.
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42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
78.70.Gq Microwave and radio-frequency interactions

Photoinduced effects in thin films of Te20As30Se50 glass with nonlinear characterization

K. Fedus, G. Boudebs, Cid B. de Araújo, M. Cathelinaud, F. Charpentier, and V. Nazabal

Appl. Phys. Lett. 94, 061122 (2009); http://dx.doi.org/10.1063/1.3082083 (3 pages) | Cited 17 times

Online Publication Date: 13 February 2009

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We discuss the influence of photoinduced effects (PIEs) on the measurements of nonlinear refractive indices and nonlinear absorption coefficients. A chalcogenide glass film Te20As30Se50 was studied using picosecond laser pulses at 1064 nm. The nonlinear imaging technique with phase object (NIT-PO) and the Z-scan technique were applied and their results are compared. The NIT-PO technique reveals clearly the influence of PIE on the samples’ response, while by using the Z-scan technique we measured the deepness of ablated regions (holes) produced during the measurements.
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78.66.Jg Amorphous semiconductors; glasses
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Difference in the nonlinear optical response of epitaxial Si on Ge(100) grown from SiH4 at 500 °C and from Si3H8 at 350 °C due to segregation of Ge

V. K. Valev, F. E. Leys, M. Caymax, and T. Verbiest

Appl. Phys. Lett. 94, 061123 (2009); http://dx.doi.org/10.1063/1.3082092 (3 pages) | Cited 3 times

Online Publication Date: 13 February 2009

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The properties of epitaxial strained Si on Ge (001) grown from SiH4 at 500 °C and from Si3H8 at 350 °C have been investigated as a function of film thickness using second harmonic generation (SHG). A clear difference in the corresponding signal amplitude, for both the interface and the “bulk” contributions, is observed. After analysis of the nonlinear susceptibility tensor components, this difference is attributed to the segregation of Ge to the SiO2/Si interface. It is demonstrated that when employed in combination with more standard experimental techniques, SHG can be a valuable tool for probing and characterizing the SiO2/Si/Ge interfaces.
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78.66.Db Elemental semiconductors and insulators
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.An Optical susceptibility, hyperpolarizability

Room-temperature operation of a 2.25 μm electrically pumped laser fabricated on a silicon substrate

J. B. Rodriguez, L. Cerutti, P. Grech, and E. Tournié

Appl. Phys. Lett. 94, 061124 (2009); http://dx.doi.org/10.1063/1.3082098 (2 pages) | Cited 7 times

Online Publication Date: 13 February 2009

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We report on a GaSb-based type-I laser structure grown by molecular beam epitaxy on a (001) silicon substrate. A thin AlSb nucleation layer followed by a 1 μm thick GaSb buffer layer was used to accommodate the very large lattice mismatch existing with the silicon substrate. Processed devices with mesa geometry exhibited laser operation in pulsed mode with a duty cycle up to 10% at room temperature.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
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Smith–Purcell frequency multiplier with synchronization of radiation from a wide electron beam

V. L. Bratman, A. E. Fedotov, P. B. Makhalov, and F. S. Rusin

Appl. Phys. Lett. 94, 061501 (2009); http://dx.doi.org/10.1063/1.3079678 (3 pages) | Cited 5 times

Online Publication Date: 9 February 2009

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An orotronlike feedback can provide a significant increase in the selectivity and power of frequency-multiplied Smith–Purcell radiation of the electron bunches formed in the course of self-excitation of a grating surface eigenmode. This method looks promising for efficient terahertz generation from both weakly and mildly relativistic electron beams.
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07.77.Ka Charged-particle beam sources and detectors
41.75.Ht Relativistic electron and positron beams
84.30.-r Electronic circuits
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