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1 Nov 2010

Volume 97, Issue 18, Articles (18xxxx)

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Appl. Phys. Lett. 97, 183105 (2010); http://dx.doi.org/10.1063/1.3506485 (3 pages)

Z. H. Zhang, X. Q. Deng, X. Q. Tan, M. Qiu, and J. B. Pan
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Efficiency droop alleviation in InGaN/GaN light-emitting diodes by graded-thickness multiple quantum wells

C. H. Wang, S. P. Chang, W. T. Chang, J. C. Li, Y. S. Lu, Z. Y. Li, H. C. Yang, H. C. Kuo, T. C. Lu, and S. C. Wang

Appl. Phys. Lett. 97, 181101 (2010); http://dx.doi.org/10.1063/1.3507891 (3 pages) | Cited 1 time

Online Publication Date: 1 November 2010

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InGaN/GaN light-emitting diodes (LEDs) with graded-thickness multiple quantum wells (GQW) was designed and grown by metal-organic chemical vapor deposition. The GQW structure, in which the well-thickness increases along [0001] direction, was found to have superior hole distribution as well as radiative recombination distribution by performing simulation modeling. Accordingly, the experimental investigation of electroluminescence spectrum reveals additional emission from the narrower wells within GQWs. Consequently, the efficiency droop can be alleviated to be about 16% from maximum at current density of 30 to 200 A/cm2, which is much smaller than that for conventional LED (32%). Moreover, the light output power was enhanced from 18.0 to 24.3 mW at 20 A/cm2.
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85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.07.St Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.05.Ea III-V semiconductors

Role of strain in polarization switching in semipolar InGaN/GaN quantum wells

Qimin Yan, Patrick Rinke, Matthias Scheffler, and Chris G. Van de Walle

Appl. Phys. Lett. 97, 181102 (2010); http://dx.doi.org/10.1063/1.3507289 (3 pages) | Cited 4 times

Online Publication Date: 2 November 2010

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The effect of strain on the valence-band structure of (11math2) semipolar InGaN grown on GaN substrates is studied. A k⋅p analysis reveals that anisotropic strain in the c-plane and shear strain are crucial for deciding the ordering of the two topmost valence bands. The shear-strain deformation potential D6 is calculated for GaN and InN using density functional theory with the Heyd–Scuseria–Ernzerhof hybrid functional [ J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 124, 219906 (2006)] . Using our deformation potentials and assuming a pseudomorphically strained structure, no polarization switching is observed. We investigate the role of partial strain relaxation in the observed polarization switching.
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81.05.Ea III-V semiconductors
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Bias-dependent absorption coefficient of the absorber section in GaN-based multisection laser diodes

W. G. Scheibenzuber, U. T. Schwarz, L. Sulmoni, J.-F. Carlin, A. Castiglia, and N. Grandjean

Appl. Phys. Lett. 97, 181103 (2010); http://dx.doi.org/10.1063/1.3514232 (3 pages) | Cited 4 times

Online Publication Date: 2 November 2010

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We measure the modal absorption coefficient of the InGaN quantum wells (QWs) in the absorber section of (Al,In)GaN multisection laser diodes as a function of bias voltage and photon energy using optical gain-spectroscopy. In the examined laser diodes, the modal absorption at the laser wavelength of 430 nm has a maximum of 270 cm−1 at low negative bias and decreases with increasing negative bias. We explain this behavior by comparing the measurements to absorption coefficients calculated from a band-edge profile simulation. The decrease of the absorption at large negative bias is caused by a shift in the transition energies in the quantum wells due to the quantum confined Stark effect.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Control of spontaneous emission from InP single quantum dots in GaInP photonic crystal nanocavities

I. J. Luxmoore, E. D. Ahmadi, N. A. Wasley, A. M. Fox, A. I. Tartakovskii, A. B. Krysa, and M. S. Skolnick

Appl. Phys. Lett. 97, 181104 (2010); http://dx.doi.org/10.1063/1.3510469 (3 pages)

Online Publication Date: 3 November 2010

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We demonstrate semiconductor quantum dots coupled to photonic crystal cavity modes operating in the visible spectrum. We present the design, fabrication, and characterization of two dimensional photonic crystal cavities in GaInP and measure quality factors in excess of 7500 at 680 nm. We demonstrate full control over the spontaneous emission rate of InP quantum dots and by spectrally tuning the exciton emission energy into resonance with the fundamental cavity mode we observe a Purcell enhancement of ∼ 8.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
78.67.Hc Quantum dots
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.40.Fy Semiconductors
73.21.La Quantum dots

Strain evaluation in AlInN/GaN Bragg mirrors by in situ curvature measurements and ex situ x-ray grazing incidence and transmission scattering

A. Krost, C. Berger, J. Bläsing, A. Franke, T. Hempel, A. Dadgar, and J. Christen

Appl. Phys. Lett. 97, 181105 (2010); http://dx.doi.org/10.1063/1.3514241 (3 pages) | Cited 2 times

Online Publication Date: 3 November 2010

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Strain in lattice matched and mismatched AlInN/GaN Bragg mirror structures were studied by in situ curvature and various ex situ x-ray measurements. In the case of lattice mismatched structures considerable deviations of the in-plane lattice parameters were evidenced near the surface region as well as in depth using x-ray grazing incidence and x-ray transmission scattering in Laue geometry. The experimental findings are explained in terms of partial stress relaxation of the AlInN/GaN Bragg layer stack with respect to the underlying GaN buffer and a mutual tensioning of the GaN and AlInN layers with respect to each other.
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78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology

Optomechanics in an ultrahigh-Q two-dimensional photonic crystal cavity

Amir H. Safavi-Naeini, Thiago P. Mayer Alegre, Martin Winger, and Oskar Painter

Appl. Phys. Lett. 97, 181106 (2010); http://dx.doi.org/10.1063/1.3507288 (3 pages) | Cited 5 times

Online Publication Date: 4 November 2010

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We demonstrate an ultrahigh-Q slotted two-dimensional photonic crystal cavity capable of obtaining strong interaction between the internal light field and the mechanical motion of the slotted structure. The measured optical quality factor is Q = 1.2×106 for a cavity with an effective modal volume of Veff = 0.04(λ)3. Optical transduction of the thermal motion of the fundamental in-plane mechanical resonance of the structure (νm = 151 MHz) is performed, from which a zero-point motion optomechanical coupling rate of g∗/2π = 320 kHz is inferred. Dynamical back-action of the optical field on the mechanical motion, resulting in cooling and amplication of the mechanical motion, is also demonstrated.
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42.79.Gn Optical waveguides and couplers
42.50.Wk Mechanical effects of light on material media, microstructures and particles

Strain influenced indium composition distribution in GaN/InGaN core-shell nanowires

Qiming Li and George T. Wang

Appl. Phys. Lett. 97, 181107 (2010); http://dx.doi.org/10.1063/1.3513345 (3 pages) | Cited 4 times

Online Publication Date: 4 November 2010

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The optical properties, indium concentration and distribution, defect morphology, and strain distribution of GaN/InGaN coaxial nanowires grown by metal organic chemical vapor deposition were investigated using spatially resolved cathodoluminescence, scanning transmission electron microscopy, and finite element analysis. The results indicate that InGaN layers with 40% or greater indium incorporation and low defect density can be achieved. The indium distribution in the InGaN shell layer was measured and qualitatively correlated with the calculated strain distribution. The three-dimensional compliance of the GaN nanowire leads to facile strain relaxation in the InGaN heteroepitaxial layer, enabling high indium incorporation and high crystalline quality.
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78.67.Lt Quantum wires
81.07.Gf Nanowires
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.60.Hk Cathodoluminescence, ionoluminescence

Effect of an asymmetry AlGaN barrier on efficiency droop in wide-well InGaN double-heterostructure light-emitting diodes

Ray-Ming Lin, Mu-Jen Lai, Liann-Be Chang, and Chou-Hsiung Huang

Appl. Phys. Lett. 97, 181108 (2010); http://dx.doi.org/10.1063/1.3513394 (3 pages) | Cited 1 time

Online Publication Date: 4 November 2010

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External-quantum-efficiency (EQE) and efficiency droop in wide-well InGaN double-heterostructure light-emitting diodes have been investigated. It was found that the insertion of an AlGaN barrier between the n-type GaN layer and the InGaN well resulted in higher peak EQE and reduced efficiency droop at a higher injection level. EQE was improved by 5.7% and 25.8% over that of a sample without an AlGaN barrier at a current density of 104.3 A/cm2 and 521 A/cm2, respectively. It is suggested that the mechanism is attributed to an electron decelerating effect that enlarges the effective active region.
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85.60.Jb Light-emitting devices

Reliability in room-temperature negative differential resistance characteristics of low-aluminum content AlGaN/GaN double-barrier resonant tunneling diodes

C. Bayram, Z. Vashaei, and M. Razeghi

Appl. Phys. Lett. 97, 181109 (2010); http://dx.doi.org/10.1063/1.3515418 (3 pages) | Cited 11 times

Online Publication Date: 5 November 2010

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AlGaN/GaN resonant tunneling diodes (RTDs), consisting of 20% (10%) aluminum-content in double-barrier (DB) active layer, were grown by metal-organic chemical vapor deposition on freestanding polar (c-plane) and nonpolar (m-plane) GaN substrates. RTDs were fabricated into 35-μm-diameter devices for electrical characterization. Lower aluminum content in the DB active layer and minimization of dislocations and polarization fields increased the reliability and reproducibility of room-temperature negative differential resistance (NDR). Polar RTDs showed decaying NDR behavior, whereas nonpolar ones did not significantly. Averaging over 50 measurements, nonpolar RTDs demonstrated a NDR of 67 Ω, a current-peak-to-valley ratio of 1.08, and an average oscillator output power of 0.52 mW.
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85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Ultrasmooth microfabricated mirrors for quantum information

G. W. Biedermann, F. M. Benito, K. M. Fortier, D. L. Stick, T. K. Loyd, P. D. D. Schwindt, C. Y. Nakakura, R. L. Jarecki, Jr., and M. G. Blain

Appl. Phys. Lett. 97, 181110 (2010); http://dx.doi.org/10.1063/1.3511743 (3 pages) | Cited 2 times

Online Publication Date: 5 November 2010

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In this paper, we realize a scalable micromirror suitable for atom chip based cavity quantum electrodynamics applications. A very low surface roughness of 2.2 Å rms on the silicon cavity mirrors is achieved using chemical dry etching along with plasma and oxidation smoothing. Our Fabry–Perot cavity comprised of these mirrors currently demonstrates the highest finesse, F = 64 000, using microfabricated mirrors. We compute a single atom cooperativity for our cavities of more than 200, making them promising candidates for detecting individual atoms and for quantum information applications on a chip.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
42.79.Bh Lenses, prisms and mirrors
42.86.+b Optical workshop techniques

Widely tunable quantum cascade lasers with coupled cavities for gas detection

Peter Fuchs, Jochen Seufert, Johannes Koeth, Julia Semmel, Sven Höfling, Lukas Worschech, and Alfred Forchel

Appl. Phys. Lett. 97, 181111 (2010); http://dx.doi.org/10.1063/1.3514247 (3 pages) | Cited 4 times

Online Publication Date: 5 November 2010

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The authors report the fabrication of widely tunable monolithic quantum cascade lasers (QCLs) with coupled Fabry–Pérot (FP) cavities on indium phosphide. Quasicontinuous tuning of the single mode emission over a total spectral range of 242 nm was realized at two regions between 8.394 and 8.785 μm. An absorption experiment with ammonia shows principle feasibility of gas detection with multisegment QCL devices. Good agreement of the experimentally observed tuning behavior with the one expected from calculated FP mode-combs indicates that the change in the refractive index is mainly due to thermal heating as a result of current injection.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Terahertz band gap properties by using metal slits in tapered parallel-plate waveguides

Eui Su Lee, Young Bin Ji, and Tae-In Jeon

Appl. Phys. Lett. 97, 181112 (2010); http://dx.doi.org/10.1063/1.3514558 (3 pages) | Cited 4 times

Online Publication Date: 5 November 2010

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We present experimental and finite-difference time-domain simulation studies on the properties of Bragg and non-Bragg band gaps; the studies are carried out by using metal slit arrays positioned at the center of the air gaps in tapered parallel-plate waveguides. Two Bragg stop bands, with a dynamic power transmission range of about 26 dB, are observed for an air gap of 29 μm. Two non-Bragg stop bands are observed for an air gap of 94 μm. Using the Ey field distribution and Poynting vectors, we confirm that the Ey field leaking from the slit and the Ey field propagating from another input vanish because they are out of phase. The Bragg and non-Bragg stop bands determined in the simulations show excellent agreement with those observed experimentally.
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42.79.Gn Optical waveguides and couplers
85.60.-q Optoelectronic devices
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