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7 Jun 2010

Volume 96, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 96, 231104 (2010); http://dx.doi.org/10.1063/1.3443734 (3 pages)

Hiroto Sekiguchi, Katsumi Kishino, and Akihiko Kikuchi
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Low efficiency droop in blue-green m-plane InGaN/GaN light emitting diodes

Shih-Chun Ling, Tien-Chang Lu, Shih-Pang Chang, Jun-Rong Chen, Hao-Chung Kuo, and Shing-Chung Wang

Appl. Phys. Lett. 96, 231101 (2010); http://dx.doi.org/10.1063/1.3449557 (3 pages) | Cited 17 times

Online Publication Date: 7 June 2010

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We investigated the electroluminescence and relatively external quantum efficiency (EQE) of m-plane InGaN/GaN light emitting diodes (LEDs) emitting at 480 nm to elucidate the droop behaviors in nitride-based LEDs. With increasing the injection current density to 100 A/cm2, the m-plane LEDs exhibit only 13% efficiency droop, whereas conventional c-plane LEDs suffer from efficiency droop at very low injection current density and the EQE of c-plane LEDs decrease to as little as 50% of its maximum value. Our simulation models show that in m-plane LEDs the absence of polarization fields manifest not only the hole distribution more uniform among the wells but also the reduction in electron overflow out of electron blocking layer. These results suggest that the nonuniform distribution of holes and electron leakage current due to strong polarization fields are responsible for the relatively significant efficiency droop of conventional c-plane LEDs.
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85.60.Jb Light-emitting devices

An alignment-free fiber-coupled microsphere resonator for gas sensing applications

Markus Gregor, Christoph Pyrlik, Rico Henze, Andreas Wicht, Achim Peters, and Oliver Benson

Appl. Phys. Lett. 96, 231102 (2010); http://dx.doi.org/10.1063/1.3430058 (3 pages) | Cited 6 times

Online Publication Date: 7 June 2010

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In this paper we report on the assembly of a robust sensor system consisting of a polystyrene microsphere resonator attached to an optical fiber taper. Since the sphere is only supported by the micrometer-sized fiber no further alignment is necessary. This results in a thermally and mechanically well isolated optical resonator system with quality factors as high as 6×105. The narrow resonances of whispering gallery modes supported by the polystyrene resonators shift with temperature at a rate of 3.8 GHz/K. Thus, a sensitive thermometer is established which allows to detect the surrounding gas via its characteristic thermal conductivity.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.79.-e Optical elements, devices, and systems

High-performance quantum ring detector for the 1–3 terahertz range

S. Bhowmick, G. Huang, W. Guo, C. S. Lee, P. Bhattacharya, G. Ariyawansa, and A. G. U. Perera

Appl. Phys. Lett. 96, 231103 (2010); http://dx.doi.org/10.1063/1.3447364 (3 pages) | Cited 2 times

Online Publication Date: 7 June 2010

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Molecular beam epitaxy of InAs/GaAs quantum dots and their subsequent transformation to quantum rings by postepitaxy thermal annealing have been investigated. Photoconductive detectors with multiple quantum ring layers in the active region exhibit dark current density ∼ 10−8 A/cm2 at a bias of 2 V at 4.2 K. The rings have a single bound state, and emission of photoexcited carriers gives rise to a spectral response peaking at 1.82 THz (165 μm) at 5.2 K. Peak responsivity of 25 A/W, specific detectivity, D∗, of 1×1016 Jones and a total quantum efficiency of 19% are measured with 1 V bias at 5.2 K. At 10 K and 1 V, D∗ ∼ 3×1015 Jones is measured.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Emission color control from blue to red with nanocolumn diameter of InGaN/GaN nanocolumn arrays grown on same substrate

Hiroto Sekiguchi, Katsumi Kishino, and Akihiko Kikuchi

Appl. Phys. Lett. 96, 231104 (2010); http://dx.doi.org/10.1063/1.3443734 (3 pages) | Cited 26 times

Online Publication Date: 7 June 2010

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A novel technology for controlling the In composition of InGaN quantum wells on the same wafer was developed, which paved the way for the monolithic integration of three-primary-color nano-light-emitting diodes. In the experiment, InGaN/GaN multiple quantum well nanocolumn arrays with nanocolumn diameters from 137 to 270 nm were prepared on the same substrate with the Ti-mask selective area growth by rf-plasma-assisted molecular beam epitaxy. The emission color changed from blue to red (from 479 to 632 nm in wavelength) with increasing nanocolumn diameter. The emission color change mechanism was clearly explained by the beam shadow effect of the neighboring nanocolumns.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Jb Light-emitting devices
81.16.-c Methods of micro- and nanofabrication and processing

Optical gain in carbon nanotubes

Etienne Gaufrès, Nicolas Izard, Xavier Le Roux, Delphine Marris-Morini, Saïd Kazaoui, Eric Cassan, and Laurent Vivien

Appl. Phys. Lett. 96, 231105 (2010); http://dx.doi.org/10.1063/1.3443634 (3 pages) | Cited 6 times

Online Publication Date: 8 June 2010

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Semiconducting single-wall carbon nanotubes (s-SWNTs) have proved to be promising material for nanophotonics and optoelectronics. Due to the possibility of tuning their direct band gap and controlling excitonic recombinations in the near-infrared wavelength range, s-SWNT can be used as efficient light emitters. We report the first experimental demonstration of room temperature intrinsic optical gain as high as 190 cm−1 at a wavelength of 1.3 μm in a thin film doped with s-SWNT. These results constitute a significant milestone toward the development of laser sources based on carbon nanotubes for future high performance integrated circuits.
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71.35.-y Excitons and related phenomena

Extraction of the β-factor for single quantum dots coupled to a photonic crystal waveguide

Henri Thyrrestrup, Luca Sapienza, and Peter Lodahl

Appl. Phys. Lett. 96, 231106 (2010); http://dx.doi.org/10.1063/1.3446873 (3 pages) | Cited 4 times

Online Publication Date: 8 June 2010

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We present measurements of the β-factor, describing the coupling efficiency of light emitted by single InAs/GaAs semiconductor quantum dots into a photonic crystal waveguide mode. The β-factor is evaluated by means of time-resolved frequency-dependent photoluminescence spectroscopy. The emission wavelength of single quantum dots is temperature tuned across the band edge of a photonic crystal waveguide and the spontaneous emission rate is recorded. Decay rates up to 5.7 ns−1, corresponding to a Purcell factor of 5.2, are measured and β-factors up to 85% are extracted. These results prove the potential of photonic crystal waveguides in the realization of on-chip single-photon sources.
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78.55.Cr III-V semiconductors
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.66.Fd III-V semiconductors

Performance improvement of longwave infrared photodetector based on type-II InAs/GaSb superlattices using unipolar current blocking layers

N. Gautam, H. S. Kim, M. N. Kutty, E. Plis, L. R. Dawson, and S. Krishna

Appl. Phys. Lett. 96, 231107 (2010); http://dx.doi.org/10.1063/1.3446967 (3 pages) | Cited 8 times

Online Publication Date: 8 June 2010

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We report here a heterojunction band gap engineered type-II InAs/GaSb strained layer superlattice photodiode for longwave infrared detection. The reported PbIbN architecture shows improved performance over conventional PIN design due to unipolar current blocking layers. At 77 K and Vb = −0.25 V, responsivity of 1.8 A/W, dark current density of 1.2 mA/cm2, single pass quantum efficiency of 23%, and shot noise limited detectivity (D∗) of 8.7×1010 cm Hz1/2 W−1 (λc = 10.8 μm) were measured. The device demonstrated background limited performance at 100 K under 300 K for 2π field of view.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Kk Junction diodes
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.70.+m Noise processes and phenomena

Enhancing optical switching with coherent control

Sunil Sandhu, Michelle L. Povinelli, and Shanhui Fan

Appl. Phys. Lett. 96, 231108 (2010); http://dx.doi.org/10.1063/1.3449572 (3 pages) | Cited 2 times

Online Publication Date: 9 June 2010

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We show that coherent control can enhance the peak pulse energy coupled into a photonic crystal (PC) resonator system. We then demonstrate two applications of this coherent control technique in a bistable PC device, namely, the reduction in input power required to switch between its bistable states and the use of phase switching to switch between its bistable states.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.70.Qs Photonic bandgap materials
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Increasing the hydrophobic property of poly (vinylidene fluoride) by KrF excimer laser irradiation

Ying Liu, Qi Wei, Yijian Jiang, and Zuoren Nie

Appl. Phys. Lett. 96, 231109 (2010); http://dx.doi.org/10.1063/1.3452343 (3 pages) | Cited 1 time

Online Publication Date: 9 June 2010

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A simple method for the fabrication of increasing the hydrophobic property on poly (vinylidene fluoride) using KrF excimer laser irradiation is demonstrated. The results showed that the water contact angle on modified area was increased from 53° to approximately 170°. It was found that the change in wetting behavior correlated with the formation of a regular wall-like structure and the appearance of C–CF2 and C–F. The combined effect of surface morphology and surface chemical construction induced by the laser irradiation had considerably contributed to increase the hydrophobic property of poly (vinylidene fluoride).
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68.08.Bc Wetting
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
68.03.Cd Surface tension and related phenomena
42.62.-b Laser applications
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.41.+e Polymers, elastomers, and plastics

Increased photocurrent in quantum dot infrared photodetector by subwavelength hole array in metal thin film

S. Hellström, Z.-H. Chen, Y. Fu, M. Qiu, R. Soltanmoradi, Q. Wang, and J. Y. Andersson

Appl. Phys. Lett. 96, 231110 (2010); http://dx.doi.org/10.1063/1.3449117 (3 pages) | Cited 6 times

Online Publication Date: 9 June 2010

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Photocurrent enhancement in quantum dot (QD) infrared photodetector (QDIP) with an optical grating of subwavelength hole array in a thin metal film has been studied by calculating the transmission and diffraction of the infrared optical field through the grating and the light-matter interaction between the transmitted optical field and electrons confined in the QD. It is shown that due to the small aspect ratio of realistic QDs in QDIPs, the light diffraction due to the surface plasmon effect at the metal-semiconductor surface and the photonic subwavelength hole array structure is dominant in increasing the photocurrent.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.21.La Quantum dots
73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
72.40.+w Photoconduction and photovoltaic effects
73.40.Ns Metal-nonmetal contacts
42.79.Dj Gratings

Surface-field cavity based on a two-dimensional cylindrical lattice

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

Appl. Phys. Lett. 96, 231111 (2010); http://dx.doi.org/10.1063/1.3428776 (3 pages) | Cited 1 time

Online Publication Date: 9 June 2010

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The results of theoretical and experimental studies of a high-Q cavity based on a cylindrical, periodic lattice are presented. The coupling of localized surface and volume electromagnetic fields results in cavity mode selection over radial, azimuthal, and longitudinal indices and formation of a high-Q cavity eigenmode. Numerical analyses of the field evolution inside the cavity were carried out. Application of these two-dimensional periodic structures in the development of high-power terahertz masers is proposed.
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42.79.Gn Optical waveguides and couplers

Fresnel reflectance in refractive index estimation of light scattering solid particles in immersion liquid

J. Räty, I. Niskanen, and K.-E. Peiponen

Appl. Phys. Lett. 96, 231112 (2010); http://dx.doi.org/10.1063/1.3449127 (3 pages) | Cited 2 times

Online Publication Date: 9 June 2010

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The refractive index of homogenous particle population can be determined by the so-called immersion liquid method. The idea is to find a known liquid whose refractive index matches the index of the particles. We report on a method that simultaneously obtains the refractive index of particles and that of the immersion liquid. It is based on a system using internal light reflection and Fresnel’s theory. The method includes a series of straightforward reflection measurements and a fitting procedure. The validity of the method was tested with CaF2 particles. The method has applications within scientific studies of microparticles and nanoparticles or micro-organism in suspensions. It can be also be utilized in industry for the detection of the refractive index of products involving particles for the purpose of improvement of product quality.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
07.60.Hv Refractometers and reflectometers

Low-threshold-current-density AlGaN-cladding-free m-plane InGaN/GaN laser diodes

R. M. Farrell, P. S. Hsu, D. A. Haeger, K. Fujito, S. P. DenBaars, J. S. Speck, and S. Nakamura

Appl. Phys. Lett. 96, 231113 (2010); http://dx.doi.org/10.1063/1.3443719 (3 pages) | Cited 16 times

Online Publication Date: 10 June 2010

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We demonstrate AlGaN-cladding-free m-plane InGaN/GaN laser diodes with threshold current densities that are comparable to state-of-the-art c-plane InGaN/GaN laser diodes. Thick InGaN waveguiding layers and a relatively wide active region with three 8 nm quantum wells were used to provide adequate refractive index contrast with the GaN cladding layers, thus eliminating the need for AlGaN cladding layers. Despite the large active region volume, lasing was achieved at a threshold current density of 1.54 kA/cm2, suggesting that the realization of even lower threshold current densities should be possible by reducing the number of quantum wells in the active region.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.81.Bm Fabrication, cladding, and splicing
42.79.Gn Optical waveguides and couplers
42.25.-p Wave optics

Upconversion of a relativistic Coulomb field terahertz pulse to the near infrared

S. P. Jamison, G. Berden, P. J. Phillips, W. A. Gillespie, and A. M. MacLeod

Appl. Phys. Lett. 96, 231114 (2010); http://dx.doi.org/10.1063/1.3449132 (3 pages) | Cited 3 times

Online Publication Date: 10 June 2010

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We demonstrate the spectral upconversion of a unipolar subpicosecond terahertz (THz) pulse, where the THz pulse is the Coulomb field of a single relativistic electron bunch. The upconversion to the optical allows remotely located detection of long wavelength and nonpropagating components of the THz spectrum, as required for ultrafast electron bunch diagnostics. The upconversion of quasimonochromatic THz radiation has also been demonstrated, allowing the observation of distinct sum- and difference-frequency mixing components in the spectrum. Polarization dependence of first and second order sidebands at ωopt±ωTHz, and ωopt±2ωTHz, respectively, confirms the χ(2) frequency mixing mechanism.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Influence of index contrast in two dimensional photonic crystal lasers

Mette Marie Jørgensen, Sidsel Rübner Petersen, Mads Brøkner Christiansen, Thomas Buß, Cameron L. C. Smith, and Anders Kristensen

Appl. Phys. Lett. 96, 231115 (2010); http://dx.doi.org/10.1063/1.3443718 (3 pages) | Cited 2 times

Online Publication Date: 11 June 2010

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The influence of index contrast variations for obtaining single-mode operation and low threshold in dye doped polymer two dimensional photonic crystal (PhC) lasers is investigated. We consider lasers made from Pyrromethene 597 doped Ormocore imprinted with a rectangular lattice PhC having a cavity in the middle of the crystal structure. We demonstrate that the index contrast, neff,high/neff,low, is an essential parameter for achieving low threshold, and we identify a trade-off between low threshold and single-mode operation.
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42.55.Mv Dye lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Tv Photonic crystal lasers and coherent effects

II–VI semiconductor color converters for efficient green, yellow, and red light emitting diodes

M. A. Haase, J. Xie, T. A. Ballen, J. Zhang, B. Hao, Z. H. Yang, T. J. Miller, X. Sun, T. L. Smith, and C. A. Leatherdale

Appl. Phys. Lett. 96, 231116 (2010); http://dx.doi.org/10.1063/1.3453447 (3 pages) | Cited 4 times

Online Publication Date: 11 June 2010

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II–VI compound semiconductor quantum-well heterostructures were fabricated for use as efficient, narrow-spectrum, photoluminescent color converters to generate green, yellow, or red light when photopumped with blue GaInN light emitting diodes (LEDs). This approach promises high efficiencies in a wide range of wavelengths that includes the green-yellow portion of the spectrum where conventional LEDs offer relatively low efficiency. External quantum conversion efficiencies of 60%–70% and output spectra with full width at half maximum of 15 nm were achieved using CdZnSe–CdMgZnSe quantum wells grown by molecular beam epitaxy on InP substrates.
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81.07.St Quantum wells
78.55.Et II-VI semiconductors
78.67.De Quantum wells
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The functionalization of graphene using electron-beam generated plasmas

M. Baraket, S. G. Walton, E. H. Lock, J. T. Robinson, and F. K. Perkins

Appl. Phys. Lett. 96, 231501 (2010); http://dx.doi.org/10.1063/1.3436556 (3 pages) | Cited 8 times

Online Publication Date: 8 June 2010

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A plasmas-based, reversible functionalization of graphene is discussed. Using electron-beam produced plasmas, oxygen and fluorine functionalities have been added by changing the processing gas mixtures from Ar/O2 to Ar/SF6, respectively. The reversibility of the functionalization was investigated by annealing the samples. The chemical composition and structural changes were studied by x-ray photoelectron spectroscopy and Raman spectroscopy.
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78.67.Wj Optical properties of graphene
64.75.Cd Phase equilibria of fluid mixtures, including gases, hydrates, etc.
78.30.Na Fullerenes and related materials
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
81.40.Gh Other heat and thermomechanical treatments
79.60.-i Photoemission and photoelectron spectra

Prediction of atmospheric pressure glow discharge in dielectric-barrier system

Xiaoxi Duan, Feng He, and Jiting Ouyang

Appl. Phys. Lett. 96, 231502 (2010); http://dx.doi.org/10.1063/1.3453451 (3 pages)

Online Publication Date: 11 June 2010

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A one-dimensional fluid model was used to investigate the breakdown mechanism and discharge mode in dielectric-barrier system. The results show that the dielectric barrier discharge mode depends strongly on the gas property (i.e., the electron multiplication). The atmospheric pressure dielectric barrier glow discharge could only be achieved in a gas (e.g., noble gas) in which the first Townsend ionization coefficient is sufficiently small and the electron multiplication does not rise up rapidly with the electric field, while could not be sustained in the gas (e.g., N2 and O2) in which the electron multiplication is sensitive to the field.
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52.80.Hc Glow; corona
52.80.Dy Low-field and Townsend discharges

Desktop megawatt superradiant free-electron laser at terahertz frequencies

Yen-Chieh Huang (黃衍介)

Appl. Phys. Lett. 96, 231503 (2010); http://dx.doi.org/10.1063/1.3447928 (3 pages) | Cited 1 time

Online Publication Date: 11 June 2010

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I present a theoretical and simulation study of a desktop, megawatt (MW), terahertz (THz) superradiance free-electron laser (FEL) driven by a THz-pulse-train photoinjector. With nominal electron parameters from a THz-pulse-train photoinjector, this superradiant FEL is capable of generating more than 5 MW power at THz frequencies from a half-meter, single-pass undulator. Tapering the undulator to a length of 1.5 m can further increase the FEL output power to nearly 15 MW.
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41.60.Cr Free-electron lasers
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Nanoscale structural variation observed on the vicinal SrTiO3(001) surface

Susumu Shiraki, Masashi Nantoh, Satoshi Katano, and Maki Kawai

Appl. Phys. Lett. 96, 231901 (2010); http://dx.doi.org/10.1063/1.3447796 (3 pages) | Cited 2 times

Online Publication Date: 7 June 2010

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The vicinal (001) surface of a Nb-doped SrTiO3 single crystal has been investigated by scanning tunneling microscopy and low energy electron diffraction. The stepped surface prepared by annealing in ultrahigh vacuum at 250 °C exhibits a complex atomic structure composed of four types of reconstructions, which shows short-range variation within nanoscale regions. SrO layers show a c(6×2) structure being stable up to 1000 °C, while √13×√13-R33.7°, c(√13×√13)-R33.7°, and c(√2×√18)-R45° structures are formed on TiO2 layers, which disappear at 450–750 °C followed by the formation of 2×2 and √5×√5-R26.6° structures. These results indicate instability of the reconstructions on the TiO2 terminated surface due to the variation in Sr adatom density caused by multikinetic processes, in contrast to the thermodynamically stable SrO terminated surface.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.40.Gh Other heat and thermomechanical treatments

Enhanced photoluminescence from self-organized rubrene single crystal surface structures

R. J. Stöhr, G. J. Beirne, P. Michler, R. Scholz, J. Wrachtrup, and J. Pflaum

Appl. Phys. Lett. 96, 231902 (2010); http://dx.doi.org/10.1063/1.3449124 (3 pages) | Cited 2 times

Online Publication Date: 7 June 2010

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We report on crystalline pyramidal structures grown via self-organization on the rubrene (001) surface. The analysis of their spectral response by means of photoluminescence with micrometer lateral resolution reveals an intensity enhancement on-top of the surface structures. As we demonstrate this intensity increase can be related to the excitation processes at the molecular level in combination with exciton confinement within the pyramids.
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78.55.Kz Solid organic materials
71.35.-y Excitons and related phenomena

Enhancing magnetorheology with nonmagnetizable particles

John C. Ulicny, Keith S. Snavely, Mark A. Golden, and Daniel J. Klingenberg

Appl. Phys. Lett. 96, 231903 (2010); http://dx.doi.org/10.1063/1.3431608 (3 pages) | Cited 3 times

Online Publication Date: 7 June 2010

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Experimental results illustrate an enhancement in the field-induced yield stress of magnetorheological (MR) fluids caused by the presence of nonmagnetizable particles. Particle-level simulations in three dimensions show similar behavior. However, the enhancement does not appear in simulations in which the spheres are confined to a monolayer. A mechanistic explanation of these observations is currently lacking. Nonetheless, the ability to enhance the MR response by replacing magnetizable particles with nonmagnetizable particles offers several advantages for applications.
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75.50.Mm Magnetic liquids
83.80.Gv Electro- and magnetorheological fluids
75.50.Tt Fine-particle systems; nanocrystalline materials

First principles prediction of the metastability of the Ge2Mn phase and its synthesis pathways

E. Arras, I. Slipukhina, M. Torrent, D. Caliste, T. Deutsch, and P. Pochet

Appl. Phys. Lett. 96, 231904 (2010); http://dx.doi.org/10.1063/1.3446837 (3 pages) | Cited 1 time

Online Publication Date: 8 June 2010

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In this letter, we performed first principles calculations to investigate the stability of a [100]-compatible Ge2Mn compound. Based on a thermodynamical approach, we propose and assess the C16 structure (Al2Cu prototype) to be only slightly metastable as compared to the other Ge–Mn compounds. The reported structural and magnetic properties of this Ge2Mn compound make it a potentially interesting compound for spintronic applications, all the more since a simple way to stabilize it as a bulk film is proposed.
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71.10.Li Excited states and pairing interactions in model systems
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Planar semipolar (10math1) GaN on (11math3) sapphire

Stephan Schwaiger, Ilona Argut, Thomas Wunderer, Rudolf Rösch, Frank Lipski, Johannes Biskupek, Ute Kaiser, and Ferdinand Scholz

Appl. Phys. Lett. 96, 231905 (2010); http://dx.doi.org/10.1063/1.3442484 (3 pages) | Cited 6 times

Online Publication Date: 8 June 2010

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We report on the growth of planar semipolar (10math1) GaN on (11math3) prepatterned sapphire. This is a method that allows the growth of semipolar oriented (10math1) GaN on large scale. Using x-ray diffraction only the peaks of the desired (10math1) plane could be observed. Scanning electron, transmission electron, and atomic force microscopy measurements show an atomically flat surface. Further investigations using photoluminescence spectroscopy show spectra that are dominated by the near band edge emission. The high crystal quality is furthermore confirmed by the small full width at half maximum values of x-ray rocking curve measurements of less than 400 arcsec.
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68.55.ag Semiconductors
68.35.Ct Interface structure and roughness
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Reduction of the transverse effective charge of optical phonons in ZnO under pressure

J. S. Reparaz, L. R. Muniz, M. R. Wagner, A. R. Goñi, M. I. Alonso, A. Hoffmann, and B. K. Meyer

Appl. Phys. Lett. 96, 231906 (2010); http://dx.doi.org/10.1063/1.3447798 (3 pages) | Cited 5 times

Online Publication Date: 9 June 2010

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From Raman scattering on a-plane wurtzite ZnO crystals we obtained a decreasing splitting between longitudinal and transversal optical phonons with A1 and E1 symmetry as a function of hydrostatic pressure up to 5.5 GPa. Consequently, the transverse effective charge (eT∗) exhibits a strong reduction with increasing pressure, yielding 2.17–14.6×10−3 P/GPa and 2.04–13.7×10−3 P/GPa (in units of the elementary charge) for the A1 and E1 phonons, respectively. We find a clear systematic in the linear pressure coefficient of eT∗ with bond polarity for the series of wide-band gap semiconductors SiC, AlN, GaN, and ZnO.
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78.30.Fs III-V and II-VI semiconductors
63.20.-e Phonons in crystal lattices
62.50.-p High-pressure effects in solids and liquids
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