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26 Sep 2011

Volume 99, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 99, 131101 (2011); http://dx.doi.org/10.1063/1.3641907 (3 pages)

Linas Minkevičius, Vincas Tamošiūnas, Irmantas Kašalynas, Dalius Seliuta, Gintaras Valušis, Alvydas Lisauskas, Sebastian Boppel, Hartmut G. Roskos, and Klaus Köhler
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Terahertz heterodyne imaging with InGaAs-based bow-tie diodes

Linas Minkevičius, Vincas Tamošiūnas, Irmantas Kašalynas, Dalius Seliuta, Gintaras Valušis, Alvydas Lisauskas, Sebastian Boppel, Hartmut G. Roskos, and Klaus Köhler

Appl. Phys. Lett. 99, 131101 (2011); http://dx.doi.org/10.1063/1.3641907 (3 pages) | Cited 3 times

Online Publication Date: 26 September 2011

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Room-temperature detection and imaging in transmission and reflection geometries at 0.591 THz with planar asymmetrically shaped InGaAs diodes (also called bow-tie diodes) are demonstrated in direct and heterodyne mode. The sensitivity of the diodes is found to be 6 V/W in direct mode, and the noise-equivalent power (NEP) in direct and heterodyne mode is estimated to be about 4 nW/mathz and 230 fW/Hz for a local-oscillator power of 11 μW, respectively. The improvement of the dynamic range by heterodyning over direct power detection amounts to about 20 dB using pixel read-out times relevant to real-time imaging conditions.
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85.30.Kk Junction diodes
84.40.-x Radiowave and microwave (including millimeter wave) technology

Impact of carrier-carrier scattering and carrier heating on pulse train dynamics of quantum dot semiconductor optical amplifiers

Niels Majer, Kathy Lüdge, Jordi Gomis-Bresco, Sabine Dommers-Völkel, Ulrike Woggon, and Eckehard Schöll

Appl. Phys. Lett. 99, 131102 (2011); http://dx.doi.org/10.1063/1.3643048 (3 pages) | Cited 4 times

Online Publication Date: 26 September 2011

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We investigate the impact of carrier-carrier scattering on the gain recovery dynamics of a quantum dot (QD) semiconductor optical amplifier. Simulations, based on semiconductor Bloch equations with microscopically calculated Coulomb scattering rates between the carrier reservoir and the QDs, show a very good agreement with experimentally obtained pump-probe dynamics over a range of injection currents. With the microscopically obtained scattering rates at hand, we can conclude that fast cascading relaxation processes between the two-dimensional carrier reservoir and the QDs in combination with carrier heating enhancing the scattering efficiency drives the ultrafast gain recovery observed in QD based semiconductor devices.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
07.60.Pb Conventional optical microscopes

Anti-bunched photons from a lateral light-emitting diode

Tommaso Lunghi, Giorgio De Simoni, Vincenzo Piazza, Christine A. Nicoll, Harvey E. Beere, David A. Ritchie, and Fabio Beltram

Appl. Phys. Lett. 99, 131103 (2011); http://dx.doi.org/10.1063/1.3643056 (3 pages)

Online Publication Date: 26 September 2011

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We demonstrate anti-bunched emission from a lateral-light emitting diode. Sub-Poissonian emission statistic, with a g(2)(0) = 0.7, is achieved at cryogenic temperature in the pulsed low-current regime, by exploiting electron injection through shallow impurities located in the diode depletion region. Thanks to its simple fabrication scheme and to its modulation bandwidth in the gigahertz range, we believe our devices are an appealing substitute for highly attenuated lasers in existing quantum-key-distribution systems. Our devices outperform strongly attenuated lasers in terms of multi-photon emission events and can therefore lead to a significant security improvement in existing quantum key distribution systems.
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85.60.Jb Light-emitting devices

Temperature dependent phonon evolutions and optical properties of highly c-axis oriented CuGaO2 semiconductor films grown by the sol-gel method

M. J. Han (韩美杰), K. Jiang (姜凯), J. Z. Zhang (张金中), Y. W. Li (李亚巍), Z. G. Hu (胡志高), and J. H. Chu (褚君浩)

Appl. Phys. Lett. 99, 131104 (2011); http://dx.doi.org/10.1063/1.3641477 (3 pages) | Cited 3 times

Online Publication Date: 26 September 2011

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Transparent conductive CuGaO2 oxide films were prepared on sapphire substrates by the sol-gel method. The highly c-axis orientation and optical transparency (60%-80%) in the visible region were obtained. It indicates that the A1g phonon mode shifts about 20 cm−1 with the temperature due to the thermal expansion of the lattice and anharmonic phonon coupling. Moreover, temperature-dependent dielectric function has been investigated and three electronic transitions located at about 1.05, 2.67, and 3.99 eV can be uniquely assigned. It was found that the optical band gap of the CuGaO2 film decreases with the temperature, which mainly originated from the electron-phonon interactions.
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68.55.ag Semiconductors
78.66.Li Other semiconductors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors
63.20.kd Phonon-electron interactions

All-optical fabrication of three-dimensional photonic crystals in photopolymers by multiplex-exposure holographic recording

Susanna Orlic, Christian Müller, and Alexander Schlösser

Appl. Phys. Lett. 99, 131105 (2011); http://dx.doi.org/10.1063/1.3644395 (3 pages) | Cited 3 times

Online Publication Date: 27 September 2011

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We develop holographic recording techniques for the versatile fabrication of three-dimensional (3D) photonic crystals in photopolymers. We introduce multiplex exposure schemes to overcome the restrictions of four-beam holographic lithography. A three-step exposure process makes it possible to fabricate hexagonal structures with three independent lattice constants. 3D photonic crystals with arbitrary geometry can be created by holographic multiplexing. Next, we extend the holographic lithography to six-beam interference to enable further design flexibility. Thick samples of different photopolymer systems are used for fabricating large-area 3D crystals. Structural properties of the fabricated crystals are investigated in a confocal laser scan setup.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.70.Qs Photonic bandgap materials
42.70.Jk Polymers and organics
42.40.-i Holography
42.70.Ln Holographic recording materials; optical storage media

Room temperature single-mode terahertz sources based on intracavity difference-frequency generation in quantum cascade lasers

Q. Y. Lu, N. Bandyopadhyay, S. Slivken, Y. Bai, and M. Razeghi

Appl. Phys. Lett. 99, 131106 (2011); http://dx.doi.org/10.1063/1.3645016 (3 pages) | Cited 11 times

Online Publication Date: 27 September 2011

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We demonstrate room temperature single-mode THz emission at 4 THz based on intracavity difference-frequency generation from mid-infrared dual-wavelength quantum cascade lasers. An integrated dual-period distributed feedback grating is defined on the cap layer to purify both mid-infrared pumping wavelengths and in turn the THz spectra. Single mode operation of the pumping wavelengths results in a single-mode THz operation with a narrow linewidth of 6.6 GHz. A maximum THz power of 8.5 μW with a power conversion efficiency of 10 μW/W2 is obtained at room temperature.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Nv Optical frequency converters
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Variable repetition frequency femtosecond-pulse surface emitting semiconductor laser

K. G. Wilcox, A. H. Quarterman, H. E. Beere, D. A. Ritchie, and A. C. Tropper

Appl. Phys. Lett. 99, 131107 (2011); http://dx.doi.org/10.1063/1.3644162 (3 pages) | Cited 5 times

Online Publication Date: 27 September 2011

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We report a femtosecond-pulse vertical-external-cavity surface-emitting laser with a continuous repetition frequency tuning range of 8% near 1 GHz. A constant average output power of 56 ± 1 mW and near-transform-limited pulse duration of 450 ± 20 fs were observed across the entire tuning range.
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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

Emission control of InGaN nanocolumns grown by molecular-beam epitaxy on Si(111) substrates

S. Albert, A. Bengoechea-Encabo, P. Lefebvre, M. A. Sanchez-Garcia, E. Calleja, U. Jahn, and A. Trampert

Appl. Phys. Lett. 99, 131108 (2011); http://dx.doi.org/10.1063/1.3644986 (3 pages) | Cited 7 times

Online Publication Date: 28 September 2011

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This work studies the effect of the growth temperature on the morphology and emission characteristics of self-assembled InGaN nanocolumns grown by plasma assisted molecular beam epitaxy. Morphology changes are assessed by scanning electron microscopy, while emission is measured by photoluminescence. Within the growth temperature range of 750 to 650 °C, an increase in In incorporation for decreasing temperature is observed. This effect allows tailoring the InGaN nanocolumns emission line shape by using temperature gradients during growth. Depending on the gradient rate, span, and sign, broad emission line shapes are obtained, covering the yellow to green range, even yielding white emission.
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81.16.Dn Self-assembly
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
61.46.-w Structure of nanoscale materials

Coherent control of a THz intersubband polarization in a voltage controlled single quantum well

M. Wagner, M. Helm, M. S. Sherwin, and D. Stehr

Appl. Phys. Lett. 99, 131109 (2011); http://dx.doi.org/10.1063/1.3644988 (3 pages) | Cited 5 times

Online Publication Date: 28 September 2011

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Ultrashort terahertz pulses in the far-infrared spectral region centered around 2 THz are used to coherently control an intersubband polarization in a GaAs/AlGaAs quantum well structure at low temperature. While the first pulse excites a macroscopic polarization, a second temporally delayed pulse switches the polarization off or refreshes it depending on the relative time delay. The switching is directly demonstrated in the time-domain for the few picosecond long free-induction decay of the induced polarization. Model calculations based on the optical Bloch equations agree well with the experimental data.
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78.67.De Quantum wells
73.30.+y Surface double layers, Schottky barriers, and work functions
78.30.Hv Other nonmetallic inorganics

GaN/SiC avalanche photodiodes

Qiugui Zhou, Dion C. McIntosh, Zhiwen Lu, Joe C. Campbell, Anand V. Sampath, Hongen Shen, and Michael Wraback

Appl. Phys. Lett. 99, 131110 (2011); http://dx.doi.org/10.1063/1.3636412 (3 pages) | Cited 2 times

Online Publication Date: 28 September 2011

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Near ultraviolet-sensitive separate absorption and multiplication avalanche photodiodes with GaN/SiC epitaxial layers grown on SiC substrate were fabricated. Dark current < 1 pA at 90% breakdown voltage, maximum multiplication gain of ∼105, and responsivity exceeding 4.2 A/W at 365 nm were achieved.
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85.60.Dw Photodiodes; phototransistors; photoresistors

Improved light output of GaN-based vertical light emitting diodes using SiO2 nanotube arrays and transparent metal oxide current conduction layer

Shui-Jinn Wang, Pei-Ren Wang, Der-Ming Kuo, Hsiun-Rong Kuo, and Jian-Shian Kuo

Appl. Phys. Lett. 99, 131111 (2011); http://dx.doi.org/10.1063/1.3645003 (3 pages) | Cited 1 time

Online Publication Date: 29 September 2011

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The use of a refractive index matching (RIM) structure with indium zinc oxide (IZO) transparent conduction layer and SiO2 nanotube (SiO2-NT) arrays to improve light extraction of vertical structure KOH-etched GaN-based light emitting diodes (VLEDs) is demonstrated. Compared to regular VLED with KOH-roughened surface, it shows considerable gains in light emitted critical angle and light output power by 21.3° and 103% at 350 mA, respectively. These improvements could be attributed to the effectiveness of the IZO/SiO2-NT RIM scheme in ameliorating current crowding and significantly minimizing the total internal reflection effect.
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85.60.Jb Light-emitting devices

Analytical expressions for spectral composition of band photoluminescence from silicon wafers and bricks

Martin A. Green

Appl. Phys. Lett. 99, 131112 (2011); http://dx.doi.org/10.1063/1.3645636 (3 pages) | Cited 4 times

Online Publication Date: 29 September 2011

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Photoluminescence imaging is now a widely used characterization tool for silicon bricks, wafers sliced from these bricks and for completed silicon devices, particularly solar cells. Analytical solutions for the spectral distribution of photoluminescence are reported showing the dependence on wavelengths of both exciting and emitted light and on test specimen doping levels, surface recombination velocities, carrier diffusion lengths, and front and rear reflection.
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78.55.Ap Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.25.+i Surface conductivity and carrier phenomena
72.80.Cw Elemental semiconductors
61.72.sh Impurity distribution

Quantitative measurement of scattering and extinction spectra of nanoparticles by darkfield microscopy

Raffaella Mercatelli, Giovanni Romano, Fulvio Ratto, Paolo Matteini, Sonia Centi, Francesca Cialdai, Monica Monici, Roberto Pini, and Franco Fusi

Appl. Phys. Lett. 99, 131113 (2011); http://dx.doi.org/10.1063/1.3636439 (3 pages) | Cited 2 times

Online Publication Date: 30 September 2011

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We demonstrate a versatile concept for the quasi simultaneous and quantitative measurement of light extinction and scattering cross section spectra of nanoparticles in a darkfield microscope. We validate this method by the analysis of an aqueous suspension of gold nanorods and comparison with both numerical simulations and standard spectrophotometry measurements. Our approach holds the promise to allow one to map the principal optical properties of nanoparticles in a biological sample with μm spatial resolution, which is an issue of particular relevance for applications in biomedical optics such as photothermolysis and laser hyperthermia.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
82.70.Kj Emulsions and suspensions
87.85.Rs Nanotechnologies-applications
78.67.Qa Nanorods
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.40.Kc Metals, semimetals, and alloys

A photonic-plasmonic structure for enhancing light absorption in thin film solar cells

Joydeep Bhattacharya, Nayan Chakravarty, Sambit Pattnaik, W. Dennis Slafer, Rana Biswas, and Vikram L. Dalal

Appl. Phys. Lett. 99, 131114 (2011); http://dx.doi.org/10.1063/1.3641469 (3 pages) | Cited 20 times

Online Publication Date: 30 September 2011

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We describe a photonic-plasmonic nanostructure, for significantly enhancing the absorption of long-wavelength photons in thin-film silicon solar cells, with the promise of exceeding the classical 4n2 limit for enhancement. We compare identical solar cells deposited on the photonic-plasmonic structure, randomly textured back reflectors and silver-coated flat reflectors. The state-of-the-art back reflectors, using annealed Ag or etched ZnO, had high diffuse and total reflectance. For nano-crystalline Si absorbers with comparable thickness, the highest absorption and photo-current of 21.5 mA/cm2 was obtained for photonic-plasmonic back-reflectors. The periodic photonic plasmonic structures scatter and reradiate light more effectively than a randomly roughened surface.
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88.40.jj Silicon solar cells
88.40.hj Efficiency and performance of solar cells
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