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16 Apr 2012

Volume 100, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 164101 (2012); http://dx.doi.org/10.1063/1.3702579 (4 pages)

Cheol-Ho Yun, Leslie Y. Yeo, James R. Friend, and Bernard Yan
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Effect of quantum well cap layer thickness on the microstructure and performance of InGaN/GaN solar cells

Yan-Ling Hu, Robert M. Farrell, Carl J. Neufeld, Michael Iza, Samantha C. Cruz, Nathan Pfaff, Dobri Simeonov, Stacia Keller, Shuji Nakamura, Steven P. DenBaars, Umesh K. Mishra, and James S. Speck

Appl. Phys. Lett. 100, 161101 (2012); http://dx.doi.org/10.1063/1.4704189 (4 pages) | Cited 2 times

Online Publication Date: 16 April 2012

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A two-step GaN barrier growth methodology was developed for InxGa1−xN/GaN multiple quantum well solar cells in which a lower temperature GaN cap layer was grown on top of the quantum wells (QWs) and then followed by a higher temperature GaN barrier layer. The performance of the solar cells improved markedly by increasing the low temperature GaN cap layer thickness from 1.5 to 3.0 nm. High-angle annular dark field scanning transmission electron microscopy and atom probe tomography measurements showed that increasing the GaN cap layer thickness improved the uniformity and increased the average indium content of the QWs.
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88.40.hj Efficiency and performance of solar cells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Mid-wave infrared HgCdTe nBn photodetector

Anne M. Itsuno, Jamie D. Phillips, and Silviu Velicu

Appl. Phys. Lett. 100, 161102 (2012); http://dx.doi.org/10.1063/1.4704359 (3 pages)

Online Publication Date: 17 April 2012

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A unipolar, barrier-integrated HgCdTe nBn photodetector with all n-type doping and a type-I band lineup is experimentally demonstrated. Planar mid-wave infrared (MWIR) nBn devices exhibit current-voltage (I-V) characteristics that are consistent with band inversion in reverse bias, indicating a barrier-influenced behavior. Dark current saturation is observed beyond a reverse bias of approximately −0.8 V. Bias-dependent photoresponse is observed in the mid-wave infrared with a cut-off wavelength around 5.7 μm. Numerical modeling based on experimental results predicts an internal peak quantum efficiency of approximately 66%.
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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

Control of absorption with hyperbolic metamaterials

T. U. Tumkur, Lei Gu, J. K. Kitur, E. E. Narimanov, and M. A. Noginov

Appl. Phys. Lett. 100, 161103 (2012); http://dx.doi.org/10.1063/1.4703931 (3 pages) | Cited 2 times

Online Publication Date: 17 April 2012

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We show that absorption of thin dye-doped polymeric films can be tuned and enhanced (nearly threefold) by metallic and lamellar metal-dielectric hyperbolic metamaterial substrates. The effect can be controlled by a combination of the substrate’s geometry and composition. As the enhancement of absorption is sustained over large range of incidence angles, the demonstrated phenomenon can lead to a variety of important applications, including solar cell technology.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
68.35.bm Polymers, organics
77.22.Ch Permittivity (dielectric function)
68.55.A- Nucleation and growth
78.66.Qn Polymers; organic compounds
42.70.Jk Polymers and organics

Strong coupling in monolithic microcavities with ZnSe quantum wells

K. Sebald, M. Seyfried, S. Klembt, S. Bley, A. Rosenauer, D. Hommel, and C. Kruse

Appl. Phys. Lett. 100, 161104 (2012); http://dx.doi.org/10.1063/1.4704188 (4 pages) | Cited 2 times

Online Publication Date: 18 April 2012

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Strong light-matter coupling is demonstrated in monolithic microcavities with only three ZnSe quantum wells embedded. Basis for this observation is the excellent structural quality of the sample as confirmed by scanning transmission electron microscopy measurements. A comparative large energy splitting between the upper and lower polariton (LP) of about 19 meV is observed by reflectivity measurements in real and k-space. Efficient polariton relaxation is shown by photoluminescence measurements at low temperatures in k-space. These beneficial properties of the sample result in a nonlinear increase of the lower polariton population in excitation density dependent measurements before the photonic cavity emission becomes dominant.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers

Spectroscopic ellipsometry of split ring resonators at infrared frequencies

M. M. Jakovljević, G. Isić, B. Vasić, T. W. H. Oates, K. Hinrichs, I. Bergmair, K. Hingerl, and R. Gajić

Appl. Phys. Lett. 100, 161105 (2012); http://dx.doi.org/10.1063/1.4703936 (4 pages) | Cited 1 time

Online Publication Date: 18 April 2012

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Using spectroscopic ellipsometry, we have determined the plasmonic resonances of split-ring resonator arrays. The features in the ellipsometric spectra were explained by the analysis of calculated polarized complex reflection spectra. The calculated near-field and current distribution revealed the nature of the resonances. The positions of Rayleigh’s anomalies are calculated and marked in the spectra. We have also shown that oblique incidence enables excitation of plasmonic modes that are not possible to excite at normal incidence.
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42.79.-e Optical elements, devices, and systems
42.87.-d Optical testing techniques

Analytic model for the efficiency droop in semiconductors with asymmetric carrier-transport properties based on drift-induced reduction of injection efficiency

Guan-Bo Lin, David Meyaard, Jaehee Cho, E. Fred Schubert, Hyunwook Shim, and Cheolsoo Sone

Appl. Phys. Lett. 100, 161106 (2012); http://dx.doi.org/10.1063/1.4704366 (4 pages) | Cited 5 times

Online Publication Date: 19 April 2012

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An analytic model is developed for the droop in the efficiency-versus-current curve for light-emitting diodes (LEDs) made from semiconductors having strong asymmetry in carrier concentration and mobility. For pn-junction diodes made of such semiconductors, the high-injection condition is generalized to include mobilities. Under high-injection conditions, electron drift in the p-type layer causes a reduction in injection efficiency. The drift-induced leakage term is shown to have a 3rd and 4th power dependence on the carrier concentration in the active region; the values of the 3rd- and 4th-order coefficients are derived. The model is suited to explain experimental efficiency-versus-current curves of LEDs.
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85.60.Jb Light-emitting devices
85.30.Kk Junction diodes

384 nm laser diode grown on a (20math1) semipolar relaxed AlGaN buffer layer

Daniel A. Haeger, Erin C. Young, Roy B. Chung, Feng Wu, Nathan A. Pfaff, Min Tsai, Kenji Fujito, Steven P. DenBaars, James S. Speck, Shuji Nakamura, and Daniel A. Cohen

Appl. Phys. Lett. 100, 161107 (2012); http://dx.doi.org/10.1063/1.4704560 (4 pages) | Cited 2 times

Online Publication Date: 19 April 2012

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We demonstrate an electrically injected semipolar (20math1) laser diode grown on a partially relaxed AlGaN buffer layer. The coherency stresses are relaxed by misfit dislocations at the GaN/AlGaN heterointerface which form by glide of preexisting threading dislocations along the (0001) basal plane. The defects are confined to the heterointerface which allows the growth of high aluminum composition films with threading dislocation densities of less than 108 cm−2. The lasing wavelength was 384 nm with a threshold current density of 15.7 kA/cm−2. UV lasers grown on semipolar relaxed AlGaN buffers provide an alternative to devices grown on AlN or sapphire.
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42.55.Px Semiconductor lasers; laser diodes
42.82.Cr Fabrication techniques; lithography, pattern transfer
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Jj Elasticity and anelasticity, stress-strain relations

Switchable hyperbolic metamaterials with magnetic control

Wei Li, Zheng Liu, Xiaogang Zhang, and Xunya Jiang

Appl. Phys. Lett. 100, 161108 (2012); http://dx.doi.org/10.1063/1.4705084 (4 pages) | Cited 2 times

Online Publication Date: 19 April 2012

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A switchable hyperbolic material (SHM) is investigated, with which one can turn on or off the hyperbolic dispersion of the material via magnetic control. The SHM has simple structure, with a one-dimensional periodic stacking of dielectric layer and gyromagnetic layer. The hyperbolic dispersion of SHM is due to the negative effective permeability of gyromagnetic layers, and it can be transformed into a regular circular dispersion when the d.c. magnetic field is switched off. This switchable dispersion transition is reversible, which may have great potential applications in many fields.
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42.70.-a Optical materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Passive harmonic mode-locking in Er-doped fiber laser based on graphene saturable absorber with repetition rates scalable to 2.22 GHz

Grzegorz Sobon, Jaroslaw Sotor, and Krzysztof M. Abramski

Appl. Phys. Lett. 100, 161109 (2012); http://dx.doi.org/10.1063/1.4704913 (4 pages) | Cited 3 times

Online Publication Date: 20 April 2012

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Passive harmonic-mode locking of erbium-doped fiber laser with atomic multilayer graphene is presented. The laser could operate at several harmonics (from 2nd to 21st) of the fundamental repetition frequency of the ring resonator (106 MHz). The highest achieved repetition rate was 2.22 GHz (which corresponds to the 21st harmonic) with sub-picosecond pulse durations and over 40 dB of the supermode noise suppression. The saturable absorber was formed by multilayer graphene, mechanically exfoliated from pure graphite block through Scotch-tape and deposited on the fiber ferrule.
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42.60.Fc Modulation, tuning, and mode locking
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.55.Wd Fiber lasers

Terahertz phase microscopy in the sub-wavelength regime

Minwoo Yi, Kanghee Lee, Jin-Dong Song, and Jaewook Ahn

Appl. Phys. Lett. 100, 161110 (2012); http://dx.doi.org/10.1063/1.4705294 (3 pages) | Cited 2 times

Online Publication Date: 20 April 2012

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Gouy phase shift is a well-known behavior that occurs when a propagating light is focused, but its behavior in the sub-wavelength confinement is not yet known. Here, we report the theoretical and experimental study of the aperture-size dependency of the Gouy phase shift in the sub-wavelength diffraction regime. In experiments carried out with laser-induced terahertz (THz) wave emission from various semiconductor apertures, we demonstrate the use of Guoy phase shit for sub-wavelength THz microscopy.
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81.05.Ea III-V semiconductors
78.70.Gq Microwave and radio-frequency interactions
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