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15 Sep 2008

Volume 93, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 93, 111901 (2008); http://dx.doi.org/10.1063/1.2980583 (3 pages)

W.-J. Lee, E.-A. Choi, J. Bang, B. Ryu, and K. J. Chang
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Structural and electronic properties of crystalline InGaO3(ZnO)m

W.-J. Lee, E.-A. Choi, J. Bang, B. Ryu, and K. J. Chang

Appl. Phys. Lett. 93, 111901 (2008); http://dx.doi.org/10.1063/1.2980583 (3 pages) | Cited 7 times

Online Publication Date: 15 September 2008

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Based on theoretical calculations, we find that the crystal structure of InGaO3(ZnO)m consists of an alternating stack of a wurtzite (Ga/Zn)–O block and an In–O octahedral layer. In the (Ga/Zn)–O block, the Ga atoms favor a modulated boundary structure against a flat boundary structure. The band spectrum shows that hole carriers are spatially confined whereas electrons move more freely through the whole crystal. The characteristics of a superlattice structure appears especially in the flat boundary structure. The band gap decreases with m due to the reduction in the quantum confinement effect.
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61.66.Fn Inorganic compounds
71.20.Ps Other inorganic compounds
72.80.Sk Insulators
72.20.Fr Low-field transport and mobility; piezoresistance
71.15.-m Methods of electronic structure calculations

Evidence of complete band gap and resonances in a plate with periodic stubbed surface

Tsung-Tsong Wu, Zi-Gui Huang, Tzu-Chin Tsai, and Tzung-Chen Wu

Appl. Phys. Lett. 93, 111902 (2008); http://dx.doi.org/10.1063/1.2970992 (3 pages) | Cited 33 times

Online Publication Date: 16 September 2008

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In this paper, we numerically and experimentally demonstrate the existence of complete band gaps and resonances in a plate with a periodic stubbed surface. Numerical results show that a complete band gap forms as the stub height reaches about three times the plate thickness. In the experiment, we used a pulsed laser to generate broadband elastic waves and used optical devices as well as point piezoelectric transducers to detect wave signals. The results show that the numerical predictions are in very good agreement with those measured experimentally. Remarkable resonances on the top surface of the stubs are found and discussed.
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42.70.Qs Photonic bandgap materials
62.30.+d Mechanical and elastic waves; vibrations

Nature of quasi-LO phonon in ZnO

Y. Y. Tay, T. T. Tan, M. H. Liang, F. Boey, and S. Li

Appl. Phys. Lett. 93, 111903 (2008); http://dx.doi.org/10.1063/1.2983656 (3 pages) | Cited 6 times

Online Publication Date: 16 September 2008

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The quasi-LO phonon mode is related to the specific defects that strongly affect the photonic properties of materials such as zinc oxide (ZnO). The line shapes of the quasi-LO phonon of ZnO annealed in different environments have been investigated. The experimental results show that this mode has the greatest Raman shift to lower wavenumber for the ZnO annealed in ambient atmosphere, suggesting that it has the largest concentration of defects that may be related to its green emission.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
61.72.Cc Kinetics of defect formation and annealing
78.20.-e Optical properties of bulk materials and thin films
78.30.Fs III-V and II-VI semiconductors

Reduction of stacking fault density in m-plane GaN grown on SiC

Y. S. Cho, Q. Sun, I.-H. Lee, T.-S. Ko, C. D. Yerino, J. Han, B. H. Kong, H. K. Cho, and S. Wang

Appl. Phys. Lett. 93, 111904 (2008); http://dx.doi.org/10.1063/1.2985816 (3 pages) | Cited 21 times

Online Publication Date: 16 September 2008

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We report the reduction in basal-plane stacking faults (BSFs) in m-plane GaN grown on m-plane SiC. The origin of BSFs is linked to heteronucleation of m-plane GaN and the presence of N-face basal-plane sidewalls of three-dimensional islands. Graded AlGaN layers help to alleviate mismatched nucleation and the generation of BSFs. Transmission electron microscopy shows that the density of BSFs is decreased to the low 105 cm−1. Anisotropy in on-axis x-ray rocking curves, a salient feature in m-plane GaN heteroepitaxial layers, is greatly reduced. A possible mechanism of BSF generation, and the demonstration of improved InGaN/GaN quantum well emission are presented.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Dd Experimental determination of defects by diffraction and scattering
78.67.De Quantum wells
78.55.Cr III-V semiconductors
61.72.Nn Stacking faults and other planar or extended defects
68.37.Og High-resolution transmission electron microscopy (HRTEM)
68.55.ag Semiconductors

Microstructural properties of phosphorus-doped p-type ZnO grown by radio-frequency magnetron sputtering

Min-Suk Oh, Dae-Kue Hwang, Yong-Seok Choi, Jang-Won Kang, Seong-Ju Park, Chi-Sun Hwang, and Kyoung Ik Cho

Appl. Phys. Lett. 93, 111905 (2008); http://dx.doi.org/10.1063/1.2936962 (3 pages) | Cited 23 times

Online Publication Date: 18 September 2008

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Phosphorus (P)-doped ZnO thin films were grown by radio-frequency magnetron sputtering to study the microstructural properties of p-type ZnO. As-grown P-doped ZnO, a semi-insulator, was converted to p-type ZnO after being annealed at 800 °C in an N2 ambient. X-ray diffraction, secondary-ion-mass spectrometry, and Hall effect measurements indicated that P2O5 phases in as-grown P-doped ZnO disappeared after thermal annealing to form a substitutional P at an O lattice site, which acts as an acceptor in P-doped ZnO. Transmission electron microscopy showed that the formation of stacking faults was facilitated to release the strain in P-doped ZnO during post-thermal annealing.
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81.15.Cd Deposition by sputtering
61.72.Cc Kinetics of defect formation and annealing
68.55.ag Semiconductors
73.61.Ga II-VI semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects

Interband and intersubband optical characterization of semipolar (11math2)-oriented GaN/AlN multiple-quantum-well structures

L. Lahourcade, P. K. Kandaswamy, J. Renard, P. Ruterana, H. Machhadani, M. Tchernycheva, F. H. Julien, B. Gayral, and E. Monroy

Appl. Phys. Lett. 93, 111906 (2008); http://dx.doi.org/10.1063/1.2978250 (3 pages) | Cited 8 times

Online Publication Date: 18 September 2008

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We report on semipolar GaN/AlN multiple-quantum-well structures grown on m-plane sapphire by plasma-assisted molecular-beam epitaxy. Optical investigation confirms a significant reduction in the quantum-confined Stark effect, in agreement with theoretical calculations, which predict an internal electric field between 0.6 and −0.55 MV/cm in the quantum wells, depending on the strain state. With respect to polar materials, the reduction in the internal electric field results in a substantial redshift of the intersubband energy.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.20.Jq Electro-optical effects
78.47.jd Time resolved luminescence
71.20.Nr Semiconductor compounds

Improved thermal management of GaN/sapphire light-emitting diodes embedded in reflective heat spreaders

R. H. Horng, C. C. Chiang, H. Y. Hsiao, X. Zheng, D. S. Wuu, and H. I. Lin

Appl. Phys. Lett. 93, 111907 (2008); http://dx.doi.org/10.1063/1.2983740 (3 pages) | Cited 12 times

Online Publication Date: 18 September 2008

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Using maskless lithography and electroforming techniques, we have demonstrated an enhanced performance of GaN/sapphire light-emitting diode (LED) embedded in a reflective copper heat spreader. The chip size and dominant wavelength of the blue emitter used in this research is 1×1 mm2 and 455 nm, respectively. The cup-shaped LED heat sink is electroformed on sapphire directly using the spin-coated photoresist coated with the Au/Cr/Ag mirror as a mold and dicing into the embedded LED with a Cu base dimension of 3×3 mm2, which effectively enhances the heat dissipation down to the metal frame and reaps the light flux generated from the side emission. With the aid of a reflective heat spreader, the encapsulated LED sample driven at 1 A yields the light output power of 700 mW and around 2.7-times increase in the wall-plug efficiency compared to that of the conventional GaN/sapphire LED. Infrared thermal images confirm the GaN/sapphire LED with more efficient heat extraction and better temperature uniformity. These results exhibit an alternative solution to thermal management of high power LED-on-sapphire samples besides the laser lift-off technique.
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85.60.Jb Light-emitting devices
85.30.Kk Junction diodes

In situ stress evolution during magnetron sputtering of transition metal nitride thin films

G. Abadias and Ph. Guerin

Appl. Phys. Lett. 93, 111908 (2008); http://dx.doi.org/10.1063/1.2985814 (3 pages) | Cited 19 times

Online Publication Date: 18 September 2008

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Stress evolution during reactive magnetron sputtering of TiN, ZrN, and TiZrN layers was studied using real-time wafer curvature measurements. The presence of stress gradients is revealed, as the result of two kinetically competing stress generation mechanisms: atomic peening effect, inducing compressive stress, and void formation, leading to a tensile stress regime predominant at higher film thickness. No stress relaxation is detected during growth interrupt in both regimes. A change from compressive to tensile stress is evidenced with increasing film thickness, Ti content, sputtering pressure, and decreasing bias voltage.
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81.15.Cd Deposition by sputtering
68.37.-d Microscopy of surfaces, interfaces, and thin films
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Self-detecting gate-tunable nanotube paddle resonators

B. Witkamp, M. Poot, H. Pathangi, A. K. Hüttel, and H. S. J. van der Zant

Appl. Phys. Lett. 93, 111909 (2008); http://dx.doi.org/10.1063/1.2985859 (3 pages) | Cited 1 time

Online Publication Date: 18 September 2008

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We have fabricated suspended metal paddle resonators with carbon nanotubes functioning as self-detecting torsional springs. We observe gate-tunable resonances that either tune to higher or to lower frequencies when increasing the dc voltage on the back gate. We attribute the former modes to flexural vibrations of the paddle resonator, while the latter ones are identified as torsional vibrations. Compared to top-down silicon fabricated paddle resonators, nanotube springs have smaller torsional spring constants and provide a larger frequency tunability.
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81.07.De Nanotubes
85.35.Kt Nanotube devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
46.40.Ff Resonance, damping, and dynamic stability

In situ measurement of stress generation arising from dislocation inclination in AlxGa1−xN:Si thin films

Jeremy D. Acord, Ian C. Manning, Xiaojun Weng, David W. Snyder, and Joan M. Redwing

Appl. Phys. Lett. 93, 111910 (2008); http://dx.doi.org/10.1063/1.2986448 (3 pages) | Cited 9 times

Online Publication Date: 18 September 2008

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The effect of Si-doping on the stress and microstructure of AlxGa1−xN (x ≈ 0.39–0.45) films grown by metalorganic chemical vapor deposition on SiC substrates was investigated. In situ measurements revealed a compressive-to-tensile transition of the stress state at the film surface upon the addition of SiH4 during growth, which correlated with a change in the angle of inclination of threading dislocations in the film. The magnitude of the in situ measured stress gradient was comparable to that predicted by the dislocation effective climb model, suggesting that dislocation inclination is the dominant mechanism responsible for tensile stress generation in the films.
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68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors
61.72.Lk Linear defects: dislocations, disclinations
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Defect-controlled growth of GaN nanorods on (0001)sapphire by molecular beam epitaxy

D. Cherns, L. Meshi, I. Griffiths, S. Khongphetsak, S. V. Novikov, N. R. S. Farley, R. P. Campion, and C. T. Foxon

Appl. Phys. Lett. 93, 111911 (2008); http://dx.doi.org/10.1063/1.2987423 (3 pages) | Cited 8 times

Online Publication Date: 18 September 2008

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Transmission electron microscopy is used to reveal threading defects in single crystal c-oriented GaN nanorods grown on (0001)sapphire by molecular beam epitaxy. The defects are shown to be planar faults lying on {10math0} planes and bounded by opposite partial screw dislocations with Burgers vectors of 1/2〈0001〉. The faults nucleate, as dislocation half-loops, from points close to the GaN/(0001)sapphire interface. It is proposed that the spiral growth of the partial atomic step joining the emerging dislocations controls nanorod growth and accounts for the growth surface morphology. The significance of these defects for nanorod growth and applications is discussed.
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81.16.-c Methods of micro- and nanofabrication and processing
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Fg Semiconductor surfaces
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Influence of symmetry mismatch on heteroepitaxial growth of perovskite thin films

D. L. Proffit, H. W. Jang, S. Lee, C. T. Nelson, X. Q. Pan, M. S. Rzchowski, and C. B. Eom

Appl. Phys. Lett. 93, 111912 (2008); http://dx.doi.org/10.1063/1.2979237 (3 pages) | Cited 7 times

Online Publication Date: 19 September 2008

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Epitaxial thin films of (110) orthorhombic CaRuO3 grown on orthorhombic (110) NdGaO3 and cubic (001) (LaAlO3)0.3–(Sr2AlTaO6)0.7 (LSAT) substrates serve as a model system isolating the influence of oxygen octahedron distortion on epitaxial growth of thin films. CaRuO3 grows as a coherent single crystal on NdGaO3 with an atomically smooth surface, whereas CaRuO3 on LSAT is multidomain with a rough surface despite the equivalent film stoichoimetry and average lattice mismatch between CaRuO3 and the substrates. Anisotropic metallic resistivity of the single crystal CaRuO3 was observed at 10 K with different electrical behaviors as a function of temperature for [math10] and [001] in-plane directions.
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68.55.A- Nucleation and growth
68.35.Ct Interface structure and roughness
68.47.Gh Oxide surfaces
73.61.Ng Insulators
61.66.Bi Elemental solids
61.66.Dk Alloys
61.66.Fn Inorganic compounds

Alloying strongly influences the structure, dynamics, and glass forming ability of metallic supercooled liquids

Y. Q. Cheng, E. Ma, and H. W. Sheng

Appl. Phys. Lett. 93, 111913 (2008); http://dx.doi.org/10.1063/1.2987727 (3 pages) | Cited 20 times

Online Publication Date: 19 September 2008

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The addition of a relatively small amount of alloying element(s) can induce major changes in the viscosity, fragility, and glass forming ability of supercooled liquids. A microscopic understanding of this behavior from the structural perspective has been elusive. Through comparisons between Cu–Zr–Al and Cu–Zr supercooled liquids, here we demonstrate the strong effects of Al alloying on the atomic-scale structure, in particular, the evolution of icosahedral local motifs, as well as the resulting dramatic slowing down of relaxation dynamics. The composition-structure-dynamics relationship uncovered for realistic bulk metallic glass forming liquids is important for understanding the glass transition and glass forming ability.
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64.70.pm Liquids
66.20.Ej Studies of viscosity and rheological properties of specific liquids
61.43.Dq Amorphous semiconductors, metals, and alloys

The atomic hydrogen flux to silicon growth flux ratio during microcrystalline silicon solar cell deposition

G. Dingemans, M. N. van den Donker, D. Hrunski, A. Gordijn, W. M. M. Kessels, and M. C. M. van de Sanden

Appl. Phys. Lett. 93, 111914 (2008); http://dx.doi.org/10.1063/1.2987519 (3 pages) | Cited 16 times

Online Publication Date: 19 September 2008

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The H flux to Si growth flux ratio is experimentally determined under state-of-the-art silicon thin-film deposition conditions by employing the recently introduced etch product detection technique. Under the technologically relevant high-pressure depletion conditions and for different process parameter settings such as pressure, SiH4 concentration, rf power, and excitation frequency, it was demonstrated that the microcrystalline to amorphous silicon phase transition is uniquely and reactor independently determined by the flux ratio of H and Si growth species.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.05.Cy Elemental semiconductors
68.55.ag Semiconductors
84.60.Jt Photoelectric conversion
81.65.Cf Surface cleaning, etching, patterning
81.10.Dn Growth from solutions
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