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28 Jun 2010

Volume 96, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 96, 261101 (2010); http://dx.doi.org/10.1063/1.3456618 (3 pages)

I. V. Konoplev, L. Fisher, A. W. Cross, A. D. R. Phelps, K. Ronald, and C. W. Robertson
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Surface wave Cherenkov maser based on a periodic lattice

I. V. Konoplev, L. Fisher, A. W. Cross, A. D. R. Phelps, K. Ronald, and C. W. Robertson

Appl. Phys. Lett. 96, 261101 (2010); http://dx.doi.org/10.1063/1.3456618 (3 pages) | Cited 7 times

Online Publication Date: 28 June 2010

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The excitation of a surface wave cavity based on a two-dimensional periodic structure by an energy source, such as relativistic electrons, results in stimulated, single frequency coherent emission. A high-Q cavity has been achieved via a resonant coupling between surface waves and volume waves. The concept of a Cherenkov maser based on the surface wave cavity is discussed and results of numerical studies presented. Links between the model described and the concept of a surface plasmon amplifier, which has been recently introduced are described.
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42.50.Pq Cavity quantum electrodynamics; micromasers
42.50.Wk Mechanical effects of light on material media, microstructures and particles

Free-standing AlxGa1−xAs heterostructures by gas-phase etching of germanium

Garrett D. Cole, Yu Bai, Markus Aspelmeyer, and Eugene A. Fitzgerald

Appl. Phys. Lett. 96, 261102 (2010); http://dx.doi.org/10.1063/1.3455104 (3 pages) | Cited 6 times

Online Publication Date: 28 June 2010

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We outline a facile fabrication technique for the realization of free-standing AlxGa1−xAs heterostructures of arbitrary aluminum content. Utilizing xenon difluoride (XeF2) we rapidly and selectively remove a sacrificial germanium (Ge) underlayer in a room temperature gas-phase etching procedure. We demonstrate two possibilities for exploiting this unique process: (1) bulk micromachining of a suspended high-frequency low-dissipation micro-optomechanical resonator consisting of an epitaxial GaAs/AlAs multilayer grown on a Ge substrate and (2) epitaxial lift-off of a GaAs film via removal of an embedded Ge sacrificial layer, resulting in lateral etch rates up to 3 mm/h and a conservative selectivity of ∼ 106.
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81.65.Cf Surface cleaning, etching, patterning
81.16.-c Methods of micro- and nanofabrication and processing
81.05.Ea III-V semiconductors
68.55.ag Semiconductors

Femtosecond laser near-field nanoablation patterning using Mie resonance high dielectric constant particle with small size parameter

Yuto Tanaka, Go Obara, Akira Zenidaka, Mitsuhiro Terakawa, and Minoru Obara

Appl. Phys. Lett. 96, 261103 (2010); http://dx.doi.org/10.1063/1.3458704 (3 pages) | Cited 4 times

Online Publication Date: 29 June 2010

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We demonstrate near-field nanohole patterning using a Mie resonance, small size parameter particle for nanofabrication technology regardless of substrate’s refractive index. Maximal enhancement factor and nearly smallest spot diameter among the same size dielectric particles are simultaneously obtainable on both low-refractive-index SiO2 and high-refractive-index Si substrates with a 200 nm particle of magnetic quadrupole resonance scattering mode (n ∼ 2.7) at 400 nm excitation wavelength. Circular nanoholes with approximately 100 nm in diameter were fabricated on both substrates using a 200 nm amorphous TiO2 particle (n = 2.66+0.024i) even with lower laser fluences than a half ablation threshold of the bare substrates.
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79.20.Eb Laser ablation
81.16.Rf Micro- and nanoscale pattern formation

Reduction in the efficiency droop effect of a light-emitting diode through surface plasmon coupling

Chih-Feng Lu, Che-Hao Liao, Chih-Yen Chen, Chieh Hsieh, Yean-Woei Kiang, and C. C. Yang

Appl. Phys. Lett. 96, 261104 (2010); http://dx.doi.org/10.1063/1.3459151 (3 pages) | Cited 8 times

Online Publication Date: 30 June 2010

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The reduction in the external quantum efficiency (EQE) droop effect of an InGaN/GaN quantum-well (QW) light-emitting diode (LED) through the mechanism of surface plasmon (SP) coupling with QW is demonstrated. With a current spreading grid pattern on the mesa surface, a smaller grid period leads to more effective carrier transport into the QW regions of Ag deposition for stronger SP–QW coupling such that the droop effect is more significantly reduced, as indicated by the increase in injection current density of maximum EQE and the decrease in drooping slope. The claim of the SP–QW coupling effect in the samples of thin p-GaN is supported by the different droop behaviors of the LED samples fabricated with another epitaxial structure of thick p-GaN, in which the SP–QW coupling effect is expected to be weak.
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85.60.Jb Light-emitting devices
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.67.De Quantum wells

Enhancement of electroluminescence in GaN-based light-emitting diodes by metallic nanoparticles

Jun-Ho Sung, Jeong Su Yang, Bo-Soon Kim, Chul-Hyun Choi, Min-Woo Lee, Seung-Gol Lee, Se-Geun Park, El-Hang Lee, and Beom-Hoan O

Appl. Phys. Lett. 96, 261105 (2010); http://dx.doi.org/10.1063/1.3457349 (3 pages) | Cited 4 times

Online Publication Date: 1 July 2010

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The enhanced electroluminescence of GaN-based light-emitting diodes (LEDs) with noble metallic nanoparticles (MNPs) is demonstrated. The sample with well-designed Ag MNPs has shown the best performance enhancement of 126% in electroluminescent intensity compared with a conventional LED sample, even though the MNPs are placed at least 200 nm away from the quantum-well active layer. The MNPs provide enhanced photon scattering and coupling between localized surface plasmon resonance (LSPR) modes and photon modes internally trapped in a device. To investigate this effect, the peculiarities of the LSPR and the corresponding structural properties of the MNPs are discussed through the effective medium approach.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

High power single-lateral-mode operation of InAs quantum dot based ridge type laser diodes by utilizing a double bend waveguide structure

Kyoung Chan Kim, Il Ki Han, Jung Il Lee, and Tae Geun Kim

Appl. Phys. Lett. 96, 261106 (2010); http://dx.doi.org/10.1063/1.3459150 (3 pages) | Cited 1 time

Online Publication Date: 1 July 2010

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We report on the high-power, single-lateral-mode operation of InAs quantum dot (QD) based ridge type laser diodes (LDs) by utilizing a double bend (DB) waveguide structure. The LDs were designed so that only fundamental modes propagate and higher optical modes are suppressed through the bent regions. DB waveguide LDs allow the use of wide ridge widths for fundamental mode operations, which helps to increase their output power via the increase in their net gain. We measured continuous wave single-lateral-mode output power of up to 310 mW from InAs QD DB waveguide LDs manufactured with 10-μm-wide stripes without facet coating.
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42.55.Px Semiconductor lasers; laser diodes
68.65.Hb Quantum dots (patterned in quantum wells)
81.05.Ea III-V semiconductors
84.40.Az Waveguides, transmission lines, striplines

Geiger-mode operation of ultraviolet avalanche photodiodes grown on sapphire and free-standing GaN substrates

E. Cicek, Z. Vashaei, R. McClintock, C. Bayram, and M. Razeghi

Appl. Phys. Lett. 96, 261107 (2010); http://dx.doi.org/10.1063/1.3457783 (3 pages) | Cited 4 times

Online Publication Date: 1 July 2010

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GaN avalanche photodiodes (APDs) were grown on both conventional sapphire and low dislocation density free-standing (FS) c-plane GaN substrates. Leakage current, gain, and single photon detection efficiency (SPDE) of these APDs were compared. At a reverse-bias of 70 V, APDs grown on sapphire substrates exhibited a dark current density of 2.7×10−4 A/cm2 whereas APDs grown on FS-GaN substrates had a significantly lower dark current density of 2.1×10−6 A/cm2. Under linear-mode operation, APDs grown on FS-GaN achieved avalanche gain as high as 14 000. Geiger-mode operation conditions were studied for enhanced SPDE. Under front-illumination the 625-μm2-area APD yielded a SPDE of ∼ 13% when grown on sapphire substrates compared to more than 24% when grown on FS-GaN. The SPDE of the same APD on sapphire substrate increased to ∼ 30% under back-illumination—the FS-GaN APDs were only tested under front illumination due to the thick absorbing GaN substrate.
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85.60.Dw Photodiodes; phototransistors; photoresistors

Nanopyramid surface plasmon resonance sensors

Pei-Yu Chung, Tzung-Hua Lin, Gregory Schultz, Christopher Batich, and Peng Jiang

Appl. Phys. Lett. 96, 261108 (2010); http://dx.doi.org/10.1063/1.3460273 (3 pages) | Cited 7 times

Online Publication Date: 1 July 2010

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We report the achievement of sensitive chemical and biological sensing using periodic gold nanopyramids with nanoscale sharp tips created by a simple and scalable colloidal templating approach. The sharp tips and the long-range periodic structure of the nanopyramid arrays enable the excitement of both localized and propagating surface plasmons. The optical reflection and the detection sensitivity of the templated nanopyramid surface plasmon resonance sensors agree reasonably well with the theoretical predictions using a finite-difference time-domain model. We have also demonstrated that specific antigen-antibody binding can be detected by using nanopyramid arrays in a real-time and label-free manner.
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87.85.Rs Nanotechnologies-applications
87.80.-y Biophysical techniques (research methods)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Effective light trapping in polycrystalline silicon thin-film solar cells by means of rear localized surface plasmons

Zi Ouyang, Supriya Pillai, Fiona Beck, Oliver Kunz, Sergey Varlamov, Kylie R. Catchpole, Patrick Campbell, and Martin A. Green

Appl. Phys. Lett. 96, 261109 (2010); http://dx.doi.org/10.1063/1.3460288 (3 pages) | Cited 31 times

Online Publication Date: 1 July 2010

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Significant photocurrent enhancement has been achieved for evaporated solid-phase-crystallized polycrystalline silicon thin-film solar cells on glass, due to light trapping provided by Ag nanoparticles located on the rear silicon surface of the cells. This configuration takes advantage of the high scattering cross-section and coupling efficiency of rear-located particles formed directly on the optically dense silicon layer. We report short-circuit current enhancement of 29% due to Ag nanoparticles, increasing to 38% when combined with a detached back surface reflector. Compared to conventional light trapping schemes for these cells, this method achieves 1/3 higher short-circuit current.
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88.40.H- Solar cells (photovoltaics)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Spatially resolved ultrafast transport current in GaAs photoswitches

L. Prechtel, S. Manus, D. Schuh, W. Wegscheider, and A. W. Holleitner

Appl. Phys. Lett. 96, 261110 (2010); http://dx.doi.org/10.1063/1.3458819 (3 pages) | Cited 3 times

Online Publication Date: 1 July 2010

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We apply a pump- and probe-scheme to coplanar stripline circuits to investigate the photocurrent response of GaAs photoswitches in time and space. We find a displacement current pulse, as reported earlier. We interpret a time-delayed second pulse as a transport current. In a time-of-flight analysis we determine the velocity of the photogenerated charge carriers in the transport current. It exceeds the Fermi and the single-particle quantum velocities. This suggests that the excitation of an electron-hole plasma and not single charge-carriers dominates the ultrafast transport current in GaAs photoswitches.
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85.60.-q Optoelectronic devices

Directional dependence of the second harmonic response in two-dimensional nonlinear photonic crystals

P. Molina, M. O. Ramírez, B. J. García, and L. E. Bausá

Appl. Phys. Lett. 96, 261111 (2010); http://dx.doi.org/10.1063/1.3459975 (3 pages) | Cited 12 times

Online Publication Date: 2 July 2010

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A two-dimensional periodic arrangement of alternating ferroelectric domains in LiNbO3, with asymmetric domain duty cycle has been used to demonstrate that counterpropagating beams along the polar axis can generate disparate second harmonic patterns, which are nonsymmetrical with respect to the source and the point of observation. These findings provide alternative routes to generate dissimilar light-matter interaction processes in two-dimensional structures assembled onto polar surfaces, including metals for plasmonics or biological compounds.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Qs Photonic bandgap materials
77.80.Dj Domain structure; hysteresis
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