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15 Dec 2008

Volume 93, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 243101 (2008); http://dx.doi.org/10.1063/1.3046098 (3 pages)

Nicholas C. Koshnick, Martin E. Huber, Julie A. Bert, Clifford W. Hicks, Jeff Large, Hal Edwards, and Kathryn A. Moler
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Interplay among multidressed four-wave mixing processes

Huaibin Zheng, Yanpeng Zhang, Zhiqiang Nie, Changbiao Li, Hong Chang, Jianping Song, and Min Xiao

Appl. Phys. Lett. 93, 241101 (2008); http://dx.doi.org/10.1063/1.3039066 (3 pages) | Cited 8 times

Online Publication Date: 15 December 2008

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We report our experimental studies of interplays between four-wave mixing (FWM) processes in multidressed two- and three-level atomic systems. The Autler–Townes splitting of the FWM signal within the electromagnetically induced transparency window has been experimentally observed. Under the same experimental conditions in different energy-level systems, the dressing effects strongly depend on the dipole moments of the transitions, which can provide an easy and qualitative way to determine the orders of magnitude of the effective dipole moments for different transitions by comparing the FWM suppressing effects.
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42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
32.60.+i Zeeman and Stark effects
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption

Power scaling of coherent terahertz pulses by stacking GaAs wafers

Yi Jiang, Yujie J. Ding, and Ioulia B. Zotova

Appl. Phys. Lett. 93, 241102 (2008); http://dx.doi.org/10.1063/1.3049592 (3 pages) | Cited 5 times

Online Publication Date: 15 December 2008

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We demonstrate that the average output power of the terahertz pulses generated by difference-frequency generation in stacked GaAs wafers is scaled up by a factor of 160. Such power scaling is made possible by achieving first-order quasiphase matching for the efficient terahertz conversion in stacked 590 μm thick (110) GaAs wafers using two CO2 laser pulses. The highest average output power is measured to be 29.8 μW by stacking ten wafers.
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84.40.-x Radiowave and microwave (including millimeter wave) technology

Multilayered optical data storage using a spatial soliton

Masaki Hisaka and Kosuke Yoshida

Appl. Phys. Lett. 93, 241103 (2008); http://dx.doi.org/10.1063/1.3050454 (3 pages)

Online Publication Date: 16 December 2008

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Multilayered optical data storage using a spatial soliton, which has the potential to increase the number of recording layers, is proposed and experimentally investigated. A Ti:sapphire pulsed laser focusing near the surface of a Ce-doped Sr0.75Ba0.25Nb2O6 crystal generated a second-harmonic (SH) beam associated with the self-focusing fundamental laser and induced SH collision responses to the counterpropagating laser pulses. Using threshold controls, single-bit data were recorded with a domain-reversal technique at the collision point, and its data were read out through a quasi-phase-matched SH generation process enhanced at the reversed domains. Multilayered recording and selective data rerecording were also demonstrated.
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42.79.Vb Optical storage systems, optical disks
42.30.-d Imaging and optical processing
42.65.Tg Optical solitons; nonlinear guided waves
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Formation of X-waves at fundamental and harmonics by infrared femtosecond pulse filamentation in air

Han Xu, Hui Xiong, Yuxi Fu, Jinping Yao, Zenghui Zhou, Ya Cheng, Zhizhan Xu, and See Leang Chin

Appl. Phys. Lett. 93, 241104 (2008); http://dx.doi.org/10.1063/1.3050523 (3 pages) | Cited 2 times

Online Publication Date: 16 December 2008

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We experimentally observe the formation of X-waves at fundamental, third harmonic, and fifth harmonic wavelengths by infrared (central wavelength at ∼ 1500 nm) femtosecond laser pulse filamentation in air. By fitting the angularly resolved spectra of the fundamental and harmonic waves using X-wave relations, we confirm that all the X-waves have nearly the same group velocity, indicating that they are locked in space and time during their propagation in filament.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Highly confined mode above the light line in a two-dimensional photonic crystal slab

Tao Xu, Mark S. Wheeler, Selvakumar V. Nair, H. E. Ruda, Mohammad Mojahedi, and J. Stewart Aitchison

Appl. Phys. Lett. 93, 241105 (2008); http://dx.doi.org/10.1063/1.3046124 (3 pages) | Cited 5 times

Online Publication Date: 16 December 2008

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We found that certain modes above the light line can satisfy total internal reflection in a two-dimensional photonic crystal slab, resulting in negligible vertical leakage. A heterogeneous cavity utilizing such a mode was designed and constructed for the microwave spectrum. Numerical calculations show the mode has a quality factor (Q) of 6×105 neglecting the material loss and 7600 including it. The measured Q (9000), resonance frequency, and mode pattern agreed well with the calculation. The mode has more than 50% of electric field energy in void space and is promising to have stronger interaction with materials introduced there.
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42.70.Qs Photonic bandgap materials
42.79.-e Optical elements, devices, and systems

Demonstration of an ultraviolet 336 nm AlGaN multiple-quantum-well laser diode

Harumasa Yoshida, Yoji Yamashita, Masakazu Kuwabara, and Hirofumi Kan

Appl. Phys. Lett. 93, 241106 (2008); http://dx.doi.org/10.1063/1.3050539 (3 pages) | Cited 30 times

Online Publication Date: 16 December 2008

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We have demonstrated laser operation of an AlGaN multiple-quantum-well (MQW) laser diode (LD) with a peak wavelength of 336.0 nm under pulsed current mode at room temperature. The LD was fabricated on a low-dislocation-density Al0.3Ga0.7N grown on a sapphire substrate using a hetero-facet-controlled epitaxial lateral overgrowth method. The laser emission is strongly transverse electric polarized with a peak output power of 3 mW and a differential external quantum efficiency of 1.1%. This demonstration of the LD lasing in ultraviolet-AII spectral band (320–340 nm) suggests that the AlGaN MQW LDs can be potent devices opening a path to deeper ultraviolet LDs.
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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.)

Multichannel filters via Γ-M and Γ-K waveguide coupling in two-dimensional triangular-lattice photonic crystal slabs

Ya-Zhao Liu, Rong-Juan Liu, Shuai Feng, Cheng Ren, Hai-Fang Yang, Dao-Zhong Zhang, and Zhi-Yuan Li

Appl. Phys. Lett. 93, 241107 (2008); http://dx.doi.org/10.1063/1.3052687 (3 pages) | Cited 11 times

Online Publication Date: 16 December 2008

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We demonstrate the design, fabrication, and characterization of a multichannel filter in a two-dimensional triangular-lattice photonic crystal slab. The output signal channel, which directs in the Γ-M crystalline direction, is orthogonal to the input signal channel that directs in the Γ-K crystalline direction. In each channel, the filtering function is guaranteed by the indirect resonant coupling between the waveguide and the cavity. Four resonant cavities with different sizes provide the mechanism of finely tuning the output wavelength. Our experimental results are in good agreement with simulations.
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42.79.Ci Filters, zone plates, and polarizers
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers

Design of midinfrared photodetectors enhanced by resonant cavities with subwavelength metallic gratings

Xinhua Hu, Ming Li, Zhuo Ye, Wai Y. Leung, Kai-Ming Ho, and Shawn-Yu Lin

Appl. Phys. Lett. 93, 241108 (2008); http://dx.doi.org/10.1063/1.3052893 (3 pages) | Cited 7 times

Online Publication Date: 16 December 2008

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We propose a metallic Fabry–Pérot cavity with a Au grating and a Au film acting as two reflectors to enhance the field and absorption in the active detector region, leading to better performance of quantum-dot-based photodetectors at a wavelength of 10 μm. One- and two-dimensional Au gratings are applied to achieve enhancement for polarized and unpolarized light, respectively. With optimizing grating parameters, the absorption can be enhanced by about 20 times in the active detector region compared to conventional photodetectors without the Au reflectors.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Dj Gratings
42.79.Wc Optical coatings
42.25.Ja Polarization
42.79.Bh Lenses, prisms and mirrors

InGaN/GaN multiple quantum wells grown on microfacets for white-light generation

Chu-Young Cho, Il-Kyu Park, Min-Ki Kwon, Ja-Yeon Kim, Seong-Ju Park, Dong-Ryul Jung, and Kwang-Woo Kwon

Appl. Phys. Lett. 93, 241109 (2008); http://dx.doi.org/10.1063/1.3049607 (3 pages) | Cited 7 times

Online Publication Date: 17 December 2008

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We report the white color electroluminescence (EL) emission from InGaN/GaN multiple quantum wells (MQWs) grown on GaN microfacets. The white color was realized by combining EL emission from InGaN/GaN MQWs on c-plane (0001), semipolar {11−22}, and {1−101} microfacets of trapezoidal n-GaN arrays. The color of EL emission was changed from reddish to bluish color with injection current and showed a white color in the current range of 180–230 mA. The variation in the color of EL emission was attributed to differences in current injection and quantum efficiency of MQWs grown on c-plane (0001) and semipolar GaN microfacets.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.05.Ea III-V semiconductors
78.60.Fi Electroluminescence

Investigation on the origin of terahertz waves generated by dc-biased multimode semiconductor lasers at room temperature

Sylwester Latkowski, Frederic Surre, Ramon Maldonado-Basilio, and Pascal Landais

Appl. Phys. Lett. 93, 241110 (2008); http://dx.doi.org/10.1063/1.3050455 (3 pages) | Cited 4 times

Online Publication Date: 18 December 2008

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A technique to measure a terahertz wave generated by spectrum tailored Fabry–Pérot lasers (FP) is assessed. A dc-biased and 25 °C temperature controlled FP is probed by a continuous wave signal, tuned at 20 nm away from its lasing modes. With a 0.02 nm resolution optical spectrum analyzer (OSA), the terahertz generated signal frequency is measured from the interval between the probe and its side-band modulations. The terahertz waves emitted by these FPs are measured at 370±5 GHz and at 1.157±0.005 THz, respectively, within a precision set by our OSA. The origin of the terahertz wave is due to passive mode-locked through intracavity four-wave-mixing processes.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Zero-group-velocity modes in longitudinally uniform waveguides

Chun Jiang, Mihai Ibanescu, J. D. Joannopoulos, and Marin Soljacic

Appl. Phys. Lett. 93, 241111 (2008); http://dx.doi.org/10.1063/1.3050459 (3 pages) | Cited 4 times

Online Publication Date: 18 December 2008

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We present a longitudinally uniform slow light waveguide, which consists of transverse periodic dielectric strips with a few defect layers. The parameters of the proposed waveguide can be tuned to have two anomalous dispersion curves with extreme points which have zero-group-velocity frequencies at nonzero wave vector in uniform-index direction. The group velocity and group velocity dispersion of the two photonic bands are analyzed, and the propagation of the slow mode with a given bandwidth is demonstrated theoretically.
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42.79.Gn Optical waveguides and couplers
42.25.Bs Wave propagation, transmission and absorption

Two-dimensional photonic crystals with germanium on insulator obtained by a condensation method

Thi-Phuong Ngo, M. El Kurdi, Xavier Checoury, Philippe Boucaud, J. F. Damlencourt, O. Kermarrec, and D. Bensahel

Appl. Phys. Lett. 93, 241112 (2008); http://dx.doi.org/10.1063/1.3054332 (3 pages) | Cited 13 times

Online Publication Date: 18 December 2008

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Germanium on insulator on silicon substrates can be obtained by the growth of a SiGe layer on silicon on insulator followed by a condensation at high temperature and a Ge epitaxial growth. We show that these substrates can be used for photonic devices. Two-dimensional photonic crystals with defect cavities have been fabricated. The emission at room temperature of condensed germanium can be spectrally controlled by varying the lattice parameter of the photonic crystals. Resonant emission is obtained between 1400 and 1700 nm when modifying the lattice periodicity between 400 and 480 nm for L3 cavities in a triangular lattice. Quality factors of 540 are obtained for the fundamental mode of the L3 cavity around 1600 nm. The experimental radiation pattern of the defect cavities is compared to the one calculated by a finite-difference time-domain method. A specificity of the germanium-on-insulator photonic crystals is that the optical sources are distributed within the whole material, by opposition to photonic crystals with a single quantum dot layer internal source.
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42.70.Qs Photonic bandgap materials
61.66.Dk Alloys
71.55.Cn Elemental semiconductors
68.55.ag Semiconductors

Subterahertz noise signal generation using a photodetector and wavelength-sliced optical noise signals for spectroscopic measurements

Ho-Jin Song, Naofumi Shimizu, Tomofumi Furuta, Atsushi Wakatsuki, and Tadao Nagatsuma

Appl. Phys. Lett. 93, 241113 (2008); http://dx.doi.org/10.1063/1.3039819 (3 pages) | Cited 2 times

Online Publication Date: 18 December 2008

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We present a photonic technique for generating a subterahertz time-continuous noise signal, which provides not only fine resolution and a potential for broadband measurements but also a higher output power resulting in high signal to noise ratio for the spectroscopy measurement. To increase the output noise power at subterahertz frequencies, the optical noise is sliced with the arrayed waveguide gratings (AWGs), resulting in the power level of −126.1 dBm/Hz at 350 GHz, which is approximately 17 dB higher than that without the AWGs. Using the implemented subterahertz noise signal source, we demonstrate a simple spectroscopic measurement of the H2O absorption line at around 380 GHz.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Gn Optical waveguides and couplers
42.79.Dj Gratings
33.20.Bx Radio-frequency and microwave spectra

Two- and three-photon absorption of semiconductor quantum dots in the vicinity of half of lowest exciton energy

Guichuan Xing, Wei Ji, Yuangang Zheng, and Jackie Y. Ying

Appl. Phys. Lett. 93, 241114 (2008); http://dx.doi.org/10.1063/1.3049132 (3 pages) | Cited 11 times

Online Publication Date: 19 December 2008

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We present a demonstration of the unambiguous determination of two-photon absorption (2PA) and three-photon absorption (3PA) in semiconductor quantum dots in the vicinity of E0/2, where E0 denotes the peak position of the lowest exciton energy. In the spectral region where photon energies ℏω ≥ E0/2, the 2PA cross section is determined by open-aperture Z scans with femtosecond laser pulses at relatively lower irradiances, and then the 3PA cross section is extracted from the Z scans measured at higher irradiances. As photon energies are less than but near E0/2, multiphoton-excited photoluminescence techniques have to be employed in conjunction with open-aperture Z scan to distinguish between 2PA and 3PA.
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78.67.Hc Quantum dots
73.21.La Quantum dots
81.05.Dz II-VI semiconductors
82.70.Dd Colloids
78.47.-p Spectroscopy of solid state dynamics
78.55.Et II-VI semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Determining the terahertz optical properties of subwavelength films using semiconductor surface plasmons

T. H. Isaac, W. L. Barnes, and E. Hendry

Appl. Phys. Lett. 93, 241115 (2008); http://dx.doi.org/10.1063/1.3049350 (3 pages) | Cited 19 times

Online Publication Date: 19 December 2008

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By employing a combination of time-domain measurements and numerical calculations, we demonstrate that the semiconductor InSb supports a strongly confined surface plasmon (SP) in the terahertz frequency range. We show that these SPs can be used to enhance the light-matter interaction with dielectric layers above the semiconductor surface, thereby allowing us to detect the presence of polystyrene layers around 1000 times thinner than the free space wavelength of the terahertz light. Finally we discuss the viability of using semiconductor SPs for the purposes of terahertz sensing and spectroscopy.
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78.70.Gq Microwave and radio-frequency interactions
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Fd III-V semiconductors
78.68.+m Optical properties of surfaces
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Formative time of breakdown modeled for the ignition of air and n-butane mixtures using effective ionization coefficients

A. A. Kudryavtsev, S. D. Popugaev, V. I. Demidov, S. F. Adams, and C. Q. Jiao

Appl. Phys. Lett. 93, 241501 (2008); http://dx.doi.org/10.1063/1.3052882 (3 pages)

Online Publication Date: 18 December 2008

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It is shown that simulations of ignition by electric arc discharge in n-butane and air mixtures have interesting features, which deviate from results obtained by simple extension of calculations based on methanelike fuels. In particular, it is demonstrated that lowering the temperature of the n-butane-air mixture before ignition under certain conditions will actually decrease the ignition stage time as well as the required electric field.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.65.-y Plasma simulation
82.33.Vx Reactions in flames, combustion, and explosions

Electrical strength of multilayer vacuum insulators

J. R. Harris, M. Kendig, B. Poole, D. M. Sanders, and G. J. Caporaso

Appl. Phys. Lett. 93, 241502 (2008); http://dx.doi.org/10.1063/1.3054344 (3 pages) | Cited 2 times

Online Publication Date: 18 December 2008

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The electrical strength of vacuum insulators is a key constraint in the design of particle accelerators and pulsed power systems. Vacuum insulating structures assembled from alternating layers of metal and dielectric can result in improved performance compared to conventional insulators, but previous attempts to optimize their design have yielded seemingly inconsistent results. Here, we present two models for the electrical strength of these structures, one assuming failure by vacuum arcing between adjacent metal layers and the other assuming failure by vacuum surface flashover. These models predict scaling laws which are in agreement with the experimental data currently available.
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84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
77.22.Jp Dielectric breakdown and space-charge effects
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

Fabrication of poly-Si films by continuous local thermal chemical vapor deposition on flexible quartz glass substrate

T. Nakamura, H. Kuraseko, K. Hanazawa, H. Koaizawa, Y. Uraoka, T. Fuyuki, and A. Mimura

Appl. Phys. Lett. 93, 241503 (2008); http://dx.doi.org/10.1063/1.3013839 (3 pages)

Online Publication Date: 18 December 2008

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The continuous deposition of polycrystalline silicon film on quartz fiber by local thermal chemical deposition was investigated. High-speed deposition owing to high temperature and locality was examined using fixed and moving substrates. We confirmed the high-speed deposition of polycrystalline silicon and achieved a maximum speed of over 1 μm/s. Furthermore, we succeeded in a continuous deposition of polycrystalline thin silicon with a thickness of 50–100 nm on a quartz fiber with low roughness and low impurity content. Thin film transistor with a mobility more than 3.7 cm2/V s was achieved by using this film.
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68.55.ag Semiconductors
73.61.Cw Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Cy Elemental semiconductors
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Nanobending of nanowires: A molecular dynamics study

Y. D. Yan, J. J. Zhang, T. Sun, W. D. Fei, Y. C. Liang, and S. Dong

Appl. Phys. Lett. 93, 241901 (2008); http://dx.doi.org/10.1063/1.3046790 (3 pages) | Cited 3 times

Online Publication Date: 15 December 2008

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Three-dimensional molecular dynamics simulations of the nanobending of copper nanowires are carried out. Simulation results show that the loading and unloading cycles of the nanobending test can reveal the full spectrum of the nanowires’ mechanical properties. Up-tensile and bottom-compressive features have been observed along with the neck zone formation. Amorphous region formation is the mechanism of fracture and final breakage. The measured elastic modulus and yield stress are 49 and 7.6 GPa, respectively. Moreover, the effect of the adhesion on the nanobending process is revealed.
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62.25.Mn Fracture/brittleness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.de Elastic moduli
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)

Infrared spectroscopy of the interface charge in a ZnO field-effect transistor

Jooyoun Kim, SungHoon Jung, E. J. Choi, Kitae Kim, Kimoon Lee, and Seongil Im

Appl. Phys. Lett. 93, 241902 (2008); http://dx.doi.org/10.1063/1.3049604 (3 pages) | Cited 2 times

Online Publication Date: 15 December 2008

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We used far-infrared transmission spectroscopy to probe the electrostatically induced charge carriers in a ZnO field-effect transistor. The carrier absorption spectrum exhibits a non-Drude, incoherent conduction behavior at low gate-source voltages (VGS<40 V), which evolves toward a standard Drude behavior as VGS is increased. This change is explained successfully by a generalized Drude model. We find that the interface carriers undergo strong backscattering collisions during the channel conduction and the microscopic scattering angle changes with VGS.
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85.30.Tv Field effect devices
78.30.Fs III-V and II-VI semiconductors

Criteria for ductility in Cr alloys based on electronic structures

Ning Ma, Bernard R. Cooper, James P. Lewis, and Bruce S. Kang

Appl. Phys. Lett. 93, 241903 (2008); http://dx.doi.org/10.1063/1.2981575 (3 pages)

Online Publication Date: 16 December 2008

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We proposed several hypotheses based on Rice’s [Mech. & Phys. of Sol. 40, 239 (1992)] brittle-dutile criterion to explain materials’ mechanical properties from their electronic structures. These criteria were used in the study of mechanisms behind the ductility enhancement in Cr alloys by MgO dispersions through first principles methods and molecular dynamics simulations. The understanding of the mechanisms may help provide systematic strategy to further improve this and other related material’s mechanical properties.
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81.40.Lm Deformation, plasticity, and creep
62.20.fk Ductility, malleability
62.20.mj Brittleness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

Transformation from an atomically stepped NiO thin film to a nanotape structure: A kinetic study using x-ray diffraction

Osami Sakata, Jia Mei Soon, Akifumi Matsuda, Yasuyuki Akita, and Mamoru Yoshimoto

Appl. Phys. Lett. 93, 241904 (2008); http://dx.doi.org/10.1063/1.3050112 (3 pages) | Cited 2 times

Online Publication Date: 16 December 2008

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Transformation from an atomically stepped epitaxial thin film of NiO to a self-assemble nanotape structure at the step edge was observed in situ using synchrotron x-ray diffraction. The pristine NiO thin film was epitaxially grown on an ultrasmooth sapphire (0001) substrate with a regular step of 0.2 nm in height using laser molecular beam epitaxy. Transformation from the thin film to the nanotape structure was facilitated by postannealing in air from room temperature to 620 K. From the Arrhenius plot of ln(in-plane domain sizes) versus 1/T, an atomic-scale transformation energy of ∼ 0.0135 eV/atom was derived.
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81.07.Bc Nanocrystalline materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Rh Phase transitions and critical phenomena
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
61.72.Cc Kinetics of defect formation and annealing

Low-temperature field-effect and magnetotransport properties in a ZnO based heterostructure with atomic-layer-deposited gate dielectric

A. Tsukazaki, A. Ohtomo, D. Chiba, Y. Ohno, H. Ohno, and M. Kawasaki

Appl. Phys. Lett. 93, 241905 (2008); http://dx.doi.org/10.1063/1.3035844 (3 pages) | Cited 8 times

Online Publication Date: 17 December 2008

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A top-gate field-effect device with atomic-layer-deposited Al2O3 dielectric was fabricated to investigate magnetotransport properties of two-dimensional electron gas (2DEG) at a semi-insulating ZnO–Mg0.12Zn0.88O double heterostructure grown by laser molecular-beam epitaxy. Hall mobility monotonically increased as the density of accumulated electrons increased. The highest mobility at 2 K was recorded to be 5000 cm2 V−1 s−1 at a 2DEG density of 1.2×1012 cm−2, which is comparable to the previously reported value for a metallic ZnO/Mg0.2Zn0.8O heterostructure. Insulator-to-metal transition was observed at a critical density of 6×1011 cm−2. The metallic-state channel exhibited Shubnikov–de Haas oscillations, demonstrating an electric-field tunable quantum device based on transparent oxide semiconductor.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.60.+g Mixed conductivity and conductivity transitions

Interpreting the change in shear band inclination angle in metallic glasses

Ming Zhao and Mo Li

Appl. Phys. Lett. 93, 241906 (2008); http://dx.doi.org/10.1063/1.3050462 (3 pages) | Cited 11 times

Online Publication Date: 17 December 2008

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Shear bands in metallic glasses subject to uniaxial loading such as tension and compression exhibit the inclination angle different from 45° on the maximum resolved shear stress plane with respect to the loading axis. The cause is often attributed to the effective normal stress acting on the shear plane, which also suggests Coulomb–Mohr yield criterion for metallic glasses. We show here that this argument is conceptually ill justified. Instead, shear band inclination angle can be described by a simple model taking into consideration the volume dilatation and the pressure effects.
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83.10.Gr Constitutive relations
71.55.Jv Disordered structures; amorphous and glassy solids
87.15.La Mechanical properties
47.11.Fg Finite element methods

Comparative study of photoluminescences for Zn-polar and O-polar faces of single-crystalline ZnO bulks

D. C. Oh, T. Kato, H. Goto, S. H. Park, T. Hanada, T. Yao, and J. J. Kim

Appl. Phys. Lett. 93, 241907 (2008); http://dx.doi.org/10.1063/1.3033224 (3 pages) | Cited 18 times

Online Publication Date: 17 December 2008

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The authors have an extensive study of photoluminescences for Zn-polar and O-polar faces of single-crystalline ZnO bulks. In the photoluminescence (PL) spectra at 10 K, Zn-polar and O-polar faces show a common emission feature: neutral donor-bound excitons and their longitudinal-optical (LO) phonon replicas are strong and free excitons are very weak. However, in the PL spectra at room temperature (RT), Zn-polar and O-polar faces show extremely different emission characteristics: the emission intensity of Zn-polar face is 30 times larger than that of O-polar face and the band edge of Zn-polar face is 33 meV redshifted from that of O-polar face. The temperature dependence of photoluminescence indicates that the PL spectra at RT are closely associated with free excitons and their phonon-assisted annihilation processes. As a result, it is found that the RT PL spectra of Zn-polar face are dominated by the first-order LO phonon replica of A free excitons, while that of O-polar face is determined by A free excitons. This is ascribed to the difference in exciton-phonon coupling strengths that Zn-polar phase has larger coupling strength than O-polar face.
Show PACS
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
63.20.kk Phonon interactions with other quasiparticles
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