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22 May 2000

Volume 76, Issue 21, pp. 2979-3144

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Influence of Cs and Ag metal vapor on output characteristics of a HyBrID copper vapor laser

Akira Ohzu, Masaaki Kato, and Yoichiro Maruyama

Appl. Phys. Lett. 76, 2979 (2000); http://dx.doi.org/10.1063/1.126551 (3 pages) | Cited 4 times

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Effects of Cs and Ag metal vapor additives on the lasing performance of a HyBrID copper vapor laser have been experimentally investigated. By adding Cs to the discharge plasma of the laser, the optimum HBr gas flow rate is changed to be smaller than that without the additives. And the average output power increases by about 20%. With the addition of Ag, the output power increases by 30%. And the output power characteristics at high-pulse repetition frequency from 16 to 20 kHz are improved. Based on a relaxation of the laser lower level of Cu atoms in the metastable state and a reduction in the remanent free electron density in the interpulse period, the mechanisms for the remarkable improvement are discussed. © 2000 American Institute of Physics.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems

Room-temperature triangular-lattice two-dimensional photonic band gap lasers operating at 1.54 μm

Jeong-Ki Hwang, Han-Youl Ryu, Dae-Sung Song, Il-Young Han, Hyun-Woo Song, Hong-Kyu Park, Yong-Hee Lee, and Dong-Hoon Jang

Appl. Phys. Lett. 76, 2982 (2000); http://dx.doi.org/10.1063/1.126552 (3 pages) | Cited 80 times

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Thermally and mechanically dependable two-dimensional (2D) photonic band gap lasers are proposed and realized at room temperature. The thin slab photonic band gap laser structure is sandwiched between air and a drilled aluminum oxide layer provided by wafer fusion techniques. In this thin slab structure, the optical confinement of photons is achieved by 2D triangular photonic lattice in horizontal plane and total internal reflection in vertical direction. Pulsed lasing action is observed at 1.54 μm by optical pumping with duty cycle up to 10%. Polarization characteristics of two-dimensional photonic band gap defect modes are also studied below and above the lasing threshold. © 2000 American Institute of Physics.
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42.60.By Design of specific laser systems
42.70.Qs Photonic bandgap materials
42.55.Px Semiconductor lasers; laser diodes

Organic light-emitting diodes using an in situ thermally polymerized hole transporting layer

Xuezhong Jiang, Sen Liu, Michelle S. Liu, Hong Ma, and Alex K.-Y. Jen

Appl. Phys. Lett. 76, 2985 (2000); http://dx.doi.org/10.1063/1.126553 (3 pages) | Cited 19 times

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We have fabricated highly efficient organic light-emitting diodes (LEDS) using in situ thermally polymerized hole transporting materials containing triphenylamine/tetraphenyldiaminobiphenyl as side chains. Double-layer LEDs made with these thermally polymerized polymers as the hole transporting layer and tris(8-hydroxyquinoline) aluminum as the emitting layer showed comparable brightness but lower turn-on voltages and better quantum efficiencies than the device made with the conventional hole transporting molecule, N-N′-diphenyl-N,N′-bis(3-methylphenyl)(1,1′-biphenyl)-4,4′-diamine. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
82.35.-x Polymers: properties; reactions; polymerization

Dynamics of carriers in resonantly excited quantum-well lasers studied by intersubband absorption

I. Shtrichman, U. Mizrahi, D. Gershoni, E. Ehrenfreund, K. D. Maranowski, and A. C. Gossard

Appl. Phys. Lett. 76, 2988 (2000); http://dx.doi.org/10.1063/1.126554 (3 pages) | Cited 3 times

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Using infrared picosecond pulses to probe the intersubband absorption of GaAs/AlGaAs quantum-well lasers following their optical excitation, we directly measure the dynamics of carriers in these devices. We find no evidence for excitonic gain even at cryogenic temperatures and resonant excitonic excitation. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.66.Fd III-V semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance

High duty cycle and continuous terahertz emission from germanium

Erik Bründermann, Danielle R. Chamberlin, and Eugene E. Haller

Appl. Phys. Lett. 76, 2991 (2000); http://dx.doi.org/10.1063/1.126555 (3 pages) | Cited 27 times

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We measured laser emission from Be-doped Ge crystals with intercontact distances as small as 0.5 mm. An improved heat sink allowed a twofold increase of the laser duty cycle to 5%. We also report the measurements of THz emission from small Be-doped Ge crystals under continuous excitation with volumes as small as 0.5 mm3. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Doping-dependent optical gain in GaN

Peter Ramvall, Yoshinobu Aoyagi, Akito Kuramata, Peter Hacke, Kay Domen, and Kazuhiko Horino

Appl. Phys. Lett. 76, 2994 (2000); http://dx.doi.org/10.1063/1.126556 (3 pages) | Cited 8 times

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We report on an investigation of the optical gain in undoped and Si-doped metal-organic vapor phase epitaxially grown GaN. For carrier densities around the Mott transition (at approximately 8×1017 cm−3), the optical gain was observed to increase from around 102 cm−1 up to about 103 cm−1, suggesting a much larger optical gain for an electron-hole plasma than for excitons. A maximum optical gain of 2700 cm−1 at an excitation density of 9.2×1018 cm−3 was found for undoped GaN. This value is the highest achieved for epitaxially grown GaN, verifying the high potential for low-threshold lasing in this material. The optical gain was observed to decrease with increasing doping density. On the contrary, the luminescence efficiency was found to increase up to a doping density of approximately 1018 cm−2. Together these effects create an optimum doping density of around 5×1017 cm−2 for stimulated emission in bulk GaN. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
61.72.uj III-V and II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.50.Mx High-frequency effects; plasma effects
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.45.+h Stimulated emission

Microlaser made of disordered media

H. Cao, J. Y. Xu, E. W. Seelig, and R. P. H. Chang

Appl. Phys. Lett. 76, 2997 (2000); http://dx.doi.org/10.1063/1.126557 (3 pages) | Cited 106 times

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We have fabricated microlasers with disordered semiconductor nanoparticles. The physical mechanism of optical confinement is based on Anderson localization of light in micrometer-sized random media. Pulsed lasing occurs around 380 nm at room temperature under optical pumping. © 2000 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
42.55.Px Semiconductor lasers; laser diodes
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
78.66.Vs Fine-particle systems
61.46.-w Structure of nanoscale materials
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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Cluster formation by barrier discharge in simulated engine exhaust gas at high temperature

John W. Hoard, Evgenii V. Kalashnikov, Joseph J. Szente, and Diane H. Podsiadlik

Appl. Phys. Lett. 76, 3000 (2000); http://dx.doi.org/10.1063/1.126558 (2 pages)

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Experiments were performed to examine cluster formation when simulated engine exhaust gas passes through an atmospheric pressure plasma discharge cell at 180 °C. The gas composition included N2, NO, CO, CO2, C3H8, C3H6, Ar, H2, H2O, O2 and SO2. Aerosol particles or clusters were measured after the gas was treated with a dielectric barrier discharge, although the quantity of clusters generated was several orders of magnitude smaller than normal engine emissions. The clusters were not formed when water was not present in the mixture. The number and size of clusters increased when hydrocarbons were not present, although the quantity was still very small. Methods to describe cluster formation phenomena are discussed. © 2000 American Institute of Physics.
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52.75.-d Plasma devices
89.60.-k Environmental studies
92.60.Sz Air quality and air pollution
52.80.-s Electric discharges

Plasma drift and nonuniformity effects in plasma immersion ion implantation

M. Keidar, O. R. Monteiro, and I. G. Brown

Appl. Phys. Lett. 76, 3002 (2000); http://dx.doi.org/10.1063/1.126559 (3 pages) | Cited 9 times

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Measurements of the ion current collected by a substrate biased to high voltage have been carried out in plasma immersion ion implantation with a filtered vacuum arc plasma source. We have found that the ion saturation current increases with applied voltage and that this effect depends upon the angle of the normal to the substrate with respect to the plasma stream and on the distance of the substrate from the plasma duct exit. We also found that the ion current increases with increasing angle of the normal to the substrate with respect to the plasma stream. A model was developed for the sheath expansion in a nonuniform plasma with substantial ion drift velocity. We find that nonuniformity and high drift velocity lead to a decrease in sheath thickness. In a nonuniform plasma, the ion saturation current increases with applied voltage. The predictions of the model were found to be in good agreement with experiment. © 2000 American Institute of Physics.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
61.72.up Other materials
52.25.Fi Transport properties
52.40.Hf Plasma-material interactions; boundary layer effects
52.65.-y Plasma simulation
52.80.Vp Discharge in vacuum
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Defect in the circular-circularly rubbed liquid crystal cell with off-center alignment

Zhizhong Zhuang, Seong-Woo Suh, Young Jin Kim, and J. S. Patel

Appl. Phys. Lett. 76, 3005 (2000); http://dx.doi.org/10.1063/1.126560 (3 pages) | Cited 2 times

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In this letter, we investigate the behavior of the defects in a circular-circularly rubbed liquid crystal cell with an off-center alignment. We show that the line defect forms a circle that passes through the rubbing centers of the two surfaces. The size and the position of the defect circle depend on the cell gap and the pitch of the materials. We propose a simple model, based on an analysis of the free energy, to explain this interesting phenomenon. This technique of defect making is useful to confine the defect to a particular position by controlling the cell parameters and the material properties. It can also be applied to the pitch measurement, the generation of the space-variant polarized light, and the study of the dynamic properties of the defect. © 2000 American Institute of Physics.
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61.30.Jf Defects in liquid crystals
61.30.Cz Molecular and microscopic models and theories of liquid crystal structure
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures

A promising pathway to make multiwalled carbon nanotubes

A. A. Setlur, S. P. Doherty, J. Y. Dai, and R. P. H. Chang

Appl. Phys. Lett. 76, 3008 (2000); http://dx.doi.org/10.1063/1.126561 (3 pages) | Cited 7 times

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Current theories for multiwalled nanotube growth (without metal catalysts) describe the growth of multiwalled nanotubes by the addition of carbon atoms, ions, or small molecules to an open ended nanotube nucleus. In this letter, we describe a method to make carbon nanotubes similar in quality to those found on the cathode deposit of the carbon arc by manipulating the heat treatment of various nongraphitizable carbon precursors. It is proposed that this method of making nanotubes via heat treatments is analogous to a graphitization process, where aromatic/graphitic fragments in disordered carbons assemble into three-dimensional graphitic structures. In addition, we have demonstrated that simple precursors, such as sucrose, can be used as starting materials. These experiments offer new opportunities to understand nanotube growth and could lead to scalable methods to make multiwalled nanotubes. © 2000 American Institute of Physics.
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81.05.ub Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.40.Gh Other heat and thermomechanical treatments

Investigation of the formation of the 2.8 eV luminescence band in p-type GaN:Mg

F. Shahedipour and B. W. Wessels

Appl. Phys. Lett. 76, 3011 (2000); http://dx.doi.org/10.1063/1.126562 (3 pages) | Cited 50 times

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The stability of defects present in GaN:Mg has been investigated using photoluminescence (PL) spectroscopy. The two dominant defect-related PL emission bands in p-type GaN were investigated, the blue band at 2.8 eV and the ultraviolet (UV) emission band at 3.27 eV. The intensity of the 3.27 eV PL band increases with increasing resistivity, whereas the 2.8 eV PL band intensity increases with a decrease in resistivity. The luminescence data is explained by a model whereby the concentration of luminescent centers depends on the Fermi level position. The shallow donor responsible for the UV band is attributed to hydrogen, whereas the deep donor defect responsible for the 2.8 eV band is attributed to a nitrogen vacancy complex. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.55.Eq III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.J- Point defects and defect clusters

Softening and mode crossing of the lowest-frequency A1(transverse-optical) phonon in single-crystal PbTiO3

Seong M. Cho and Hyun M. Jang

Appl. Phys. Lett. 76, 3014 (2000); http://dx.doi.org/10.1063/1.126563 (3 pages) | Cited 24 times

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The polarized Raman spectra of high-quality single-crystal PbTiO3 were measured in the temperature range between 300 and 700 K. The soft-mode behavior of the A1(1TO) (transverse- optical) phonon was observed directly. Above 400 K, however, an intensity transfer between the subpeaks of the A1(1TO) mode was observed, and the line shape of the A1(1TO) mode strongly deviated from the theoretical prediction based on the harmonic approximation in the interatomic potential. In addition, the mode crossing between the A1(1TO) phonon and the E(1LO) (longitudinal optical) phonon was observed. The observed mode crossing behavior clearly supports the assignment of the E(1LO) and A1(1TO) modes, which was originally suggested by Foster and co-workers [Phys. Rev. Lett. 71, 1258 (1993)]. © 2000 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
78.30.Hv Other nonmetallic inorganics

Mechanical behavior of thin buffer layers in InAs/GaAs(111)A heteroepitaxy

Rodney I. Pelzel, Luis A. Zepeda-Ruiz, Brett Z. Nosho, Youli Li, W. Henry Weinberg, and Dimitrios Maroudas

Appl. Phys. Lett. 76, 3017 (2000); http://dx.doi.org/10.1063/1.126564 (3 pages) | Cited 4 times

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The mechanical behavior of thin buffer layers for InAs/GaAs(111)A heteroepitaxy has been investigated by x-ray diffraction (XRD). XRD θ–2θ spectra are presented for the (220) reflection for two monolayers (MLs) of InAs deposited on GaAs buffer layers of both 20 ML and 150 nm (≅ 460 ML) in thickness. For the thicker buffer layer, the XRD spectrum exhibits a single, symmetric peak at a reflected angle corresponding to the bulk GaAs lattice parameter, while for the thinner one it exhibits asymmetry around the GaAs substrate reflection with the spectrum tailing to lower angle. This indicates that the thin buffer layer possesses a distribution of interlayer distances in the [220] direction that are larger than that of the GaAs substrate. The XRD data agree very well with theoretical calculations in which the thin GaAs buffer layer is modeled as unconstrained at its base. Our results provide direct evidence that thin GaAs buffer layers behave mechanically similarly to compliant substrates. © 2000 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Silicon nanowires grown on iron-patterned silicon substrates

Qian Gu, Haiyan Dang, Jien Cao, Jianhong Zhao, and Shoushan Fan

Appl. Phys. Lett. 76, 3020 (2000); http://dx.doi.org/10.1063/1.126565 (2 pages) | Cited 20 times

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This letter reports the synthesis of silicon nanowires on iron-patterned silicon substrates in a controlled fashion using a method involving thermal evaporation of pure silicon powder. The positions of these silicon nanowires were controlled by depositing iron in desired areas on the substrates. Transmission electron microscopy, high-resolution transmission electron microscopy, and scanning electron microscopy images indicate that the products are straight crystalline silicon nanowires with diameters of 10–60 nm. The formation mechanism of the nanowires is discussed. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.05.Cy Elemental semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.07.-b Nanoscale materials and structures: fabrication and characterization

Stabilization of strained alloy film growth by a difference in atomic mobilities

B. J. Spencer, P. W. Voorhees, and J. Tersoff

Appl. Phys. Lett. 76, 3022 (2000); http://dx.doi.org/10.1063/1.126566 (3 pages) | Cited 24 times

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We analyze the development of compositional and surface nonuniformities during the growth of strained alloy films, for the case of different surface mobilities of the alloy components. We find that a difference in surface mobilities can completely suppress the stress-driven morphological instability. The stabilization occurs under compressive misfit when one atomic species is both large and fast relative to the other, and similarly under tensile misfit when one species is small and fast. © 2000 American Institute of Physics.
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68.55.Nq Composition and phase identification
68.55.-a Thin film structure and morphology
68.35.Fx Diffusion; interface formation
68.35.Dv Composition, segregation; defects and impurities

Optical characterization of high-purity cubic GaN grown on GaAs (001) substrate by metalorganic chemical vapor deposition

Dapeng Xu, Hui Yang, J. B. Li, D. G. Zhao, S. F. Li, S. M. Zhuang, R. H. Wu, Y. Chen, and G. H. Li

Appl. Phys. Lett. 76, 3025 (2000); http://dx.doi.org/10.1063/1.126567 (3 pages) | Cited 6 times

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The optical properties of cubic GaN films have been investigated in the temperature range of 10–300 K. Five peaks were observed at 10 K. From the dependence of photoluminescence emissions on the temperature and excitation intensity, we have assigned two of the five peaks (2.926 and 2.821 eV) to donor–acceptor pair (DAP) transitions. Furthermore, these two peaks were found to be related to a common shallow donor involved in the peak position previously reported at 3.150 eV. The intensities of DAP transitions were much weaker than that of excitonic emission even at low temperature, indicating a relatively high purity of our samples. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.55.Eq III-V semiconductors

Growth of AlGaN on Si(111) by gas source molecular beam epitaxy

S. A. Nikishin, N. N. Faleev, A. S. Zubrilov, V. G. Antipov, and H. Temkin

Appl. Phys. Lett. 76, 3028 (2000); http://dx.doi.org/10.1063/1.126568 (3 pages) | Cited 15 times

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Gas source molecular beam epitaxy with ammonia was used to grow AlxGa1−xN on Si(111). Three types of buffer layers, containing AlN, AlGaN/AlN, and AlGaN/GaN short period superlattices, were used and their effectiveness evaluated by x-ray diffraction. We determined that a combination of AlN buffer layer, prepared under the two-dimensional growth mode, with a short period superlattice of AlGaN/GaN results in the highest quality AlGaN. Under optimized growth conditions, x-ray diffraction coherence length almost equal to the layer thickness was obtained for low Al content layers. The normalized coherence length was reduced to ∼0.4 for x=0.66 and it increased again to ∼0.75 in AlN. From room temperature band edge cathodoluminescence of AlGaN grown on Si(111) we determined the alloy bowing coefficient of b=1.5 eV, in good agreement with previous results obtained by absorption measurements. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.05.Ea III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors

Spatially resolved band-edge emission from partially coalesced GaN pyramids prepared by epitaxial lateral overgrowth

X. Li, P. W. Bohn, Jeongyong Kim, J. O. White, and J. J. Coleman

Appl. Phys. Lett. 76, 3031 (2000); http://dx.doi.org/10.1063/1.126569 (3 pages) | Cited 11 times

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Partially coalesced GaN pyramidal structures are formed by metal-organic chemical vapor deposition using the epitaxial lateral overgrowth method. Spatially resolved optical characterization of these structures has been carried out using cathodoluminescence (CL) microscopy and spectroscopy. The coalesced region exhibits much stronger and more uniform luminescence than other regions of the sample. In addition, the emission from the coalesced region is blue-shifted, while that from the sidewalls is red-shifted, relative to broad area grown samples. The peak shift mechanism is discussed based on the CL temperature and power dependence and analysis of the confocal Raman scattering. © 2000 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Desorption of organic species from the GaAs (100) surface at low temperatures using low energy electron irradiation in a hydrogen ambient

Y. Chen, J. Schmidt, L. Šiller, J. C. Barnard, R. E. Palmer, T. M. Burke, M. P. Smith, S. J. Brown, D. A. Ritchie, and M. Pepper

Appl. Phys. Lett. 76, 3034 (2000); http://dx.doi.org/10.1063/1.126570 (3 pages) | Cited 1 time

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We present a technique for the controlled removal of organic adsorbates from the GaAs (100) surface incorporating hydrogen dosing (atomic or molecular) combined with low-energy electron irradiation. High-resolution electron energy-loss and Auger electron spectroscopes verify a considerable desorption of carbon/hydrocarbons following electron irradiation at 50 eV under a hydrogen atom flux even at room temperature. At a sample temperature of 500 °C, static secondary ion mass spectroscopy data demonstrate selective area removal of carbon from the surface following 25 eV electron irradiation in a molecular hydrogen ambient, with a desorption rate controlled by the incident electron flux. © 2000 American Institute of Physics.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
79.20.La Photon- and electron-stimulated desorption
81.65.Cf Surface cleaning, etching, patterning
68.35.Dv Composition, segregation; defects and impurities
79.20.Fv Electron impact: Auger emission
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Nano-icosahedral quasicrystalline phase formation from a supercooled liquid state in Zr–Fe–Ni ternary metallic glass

Junji Saida, Chunfei Li, Mitsuhide Matsushita, and Akihisa Inoue

Appl. Phys. Lett. 76, 3037 (2000); http://dx.doi.org/10.1063/1.126571 (3 pages) | Cited 7 times

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It was found that an icosahedral quasicrystalline phase was formed as a primary precipitation phase from the supercooled liquid region of the melt-spun Zr70Fe20Ni10 ternary metallic glass. The precipitation of an icosahedral phase takes place at 673 K at the heating rate of 0.67 K s−1. The precipitated icosahedral particle has a nearly spherical morphology and a fine grain size in the diameter range of 5–10 nm. The second crystallization reaction proceeds through a broad exothermic peak and results in the formation of Zr2Ni and Zr2Fe phases. The formation of nanoscale icosahedral phase by the addition of Fe as well as noble metals such as Pd, Au, and Pt indicates the possibility of existence of an icosahedral short-range order in the various Zr-based metallic glasses. © 2000 American Institute of Physics.
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61.44.Br Quasicrystals
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
61.43.Fs Glasses
81.05.Bx Metals, semimetals, and alloys

Well-width dependence of the quantum efficiencies of GaN/AlxGa1−xN multiple quantum wells

K. C. Zeng, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 76, 3040 (2000); http://dx.doi.org/10.1063/1.126572 (3 pages) | Cited 26 times

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A set of GaN/AlxGa1−xN(x ≈ 0.2) multiple quantum wells (MQWs) with well widths, Lw, varying from 6 to 48 Å has been grown by metalorganic chemical vapor deposition under the optimal GaN-like growth conditions. Picosecond time-resolved photoluminescence spectroscopy has been employed to probe the well-width dependence of the quantum efficiencies (QE) of these MQWs. Our results have shown that these GaN/AlGaN MQW structures exhibit negligibly small piezoelectric effects and hence enhanced QE. Furthermore, GaN/AlxGa1−xN MQWs with Lw between 12 and 42 Å were observed to provide the highest QE, which can be attributed to the reduced nonradiative recombination rate as well as the improved quantum-well quality. The decreased QE in GaN/AlxGa1−xN MQWs with Lw<12 Å is due to the enhanced carrier leakage to the underlying GaN epilayers, while the decreased QE in MQWs with Lw>42 Å is associated with an increased nonradiative recombination rate as Lw approaching the critical thickness of MQWs. The implications of our results on device applications are also discussed. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Correlation between strain and dielectric properties in ZrTiO4 thin films

Taeseok Kim, Jeongmin Oh, Byungwoo Park, and Kug Sun Hong

Appl. Phys. Lett. 76, 3043 (2000); http://dx.doi.org/10.1063/1.126573 (3 pages) | Cited 35 times

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Single-phase paraelectric ZrTiO4 thin films were synthesized at various temperatures using direct-current magnetron reactive sputtering. The dielectric constants (ε) and dielectric losses (tan δ) of as-deposited and annealed films were measured in the 100 kHz range using a Pt upper electrode and a phosphorous-doped Si (100) bottom electrode. Data showed that as the deposition temperature increased, the dielectric losses decreased, while the dielectric constants did not change much. Similar trends for dielectric losses were observed after annealing at 800 °C. These results of dielectric losses correlated well with strains in ZrTiO4 thin films, analyzed from x-ray diffraction peak widths at various scattering angles. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Gm Dielectric loss and relaxation
81.15.Cd Deposition by sputtering
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.22.Ch Permittivity (dielectric function)
68.60.Bs Mechanical and acoustical properties

Effect of strain transfer on critical thickness for epitaxial layers grown on compliant substrate

F. Y. Huang

Appl. Phys. Lett. 76, 3046 (2000); http://dx.doi.org/10.1063/1.126574 (3 pages) | Cited 9 times

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The critical thickness of strained layers grown on a thin-film substrate is analyzed based on an equilibrium theory. Due to the strain transfer from the epitaxial layer to the underneath substrate, the critical thickness increases as the substrate thickness decreases. Ultimately, there exists a threshold thickness for the substrate below which mismatched epitaxial layers of any thickness can be grown without dislocations. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.60.Bs Mechanical and acoustical properties
61.72.Bb Theories and models of crystal defects

Vertical motional narrowing of exciton polaritons in GaN based multiple quantum wells

Guillaume Malpuech and Alexey Kavokin

Appl. Phys. Lett. 76, 3049 (2000); http://dx.doi.org/10.1063/1.126575 (3 pages) | Cited 6 times

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Numerical simulation of time-resolved light reflection from GaN/AlGaN single and multiquantum wells (MQWs) revealed a pronounced vertical motional narrowing effect. This effect consists in reduction of the inhomogeneous broadening of the exciton peaks and increase of the decay time of the time-resolved reflection due to the averaging of the vertical disorder in the structure by extended exciton-polariton modes. The theory predicts pronounced oscillations in the time-resolved reflection of MQWs resulting from the interference of exciton-polariton modes in the structure. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.-y Excitons and related phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.47.-p Spectroscopy of solid state dynamics
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