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18 Sep 2000

Volume 77, Issue 12, pp. 1741-1913

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Low-threshold and high power λ ∼ 9.0 μm quantum cascade lasers operating at room temperature

A. Matlis, S. Slivken, A. Tahraoui, K. J. Luo, J. Diaz, Z. Wu, A. Rybaltowski, C. Jelen, and M. Razeghi

Appl. Phys. Lett. 77, 1741 (2000); http://dx.doi.org/10.1063/1.1310632 (3 pages) | Cited 12 times

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We report a low threshold current density and high power for λ ∼ 9 μmAlInAs/GaInAs quantum cascade lasers operating at room temperature. The threshold current density is 1.95 kA/cm2 at 300 K and 0.61 kA/cm2 at 80 K for 5 μs pulses at 200 Hz repetition rate. The peak output power is 700 mW at room temperature and 1.3 W at 80 K per two facets for cavity length is 3 mm with a stripe width of 20 μm. The characteristic temperature T0 is 185 °C. The slope efficiency is 450 and 800 mW/A at 300 and 80 K, respectively. In continuous wave operation, the output power is more than 150 mW at 80 K and 25 mW at 140 K. This high performance was achieved by improving the material growth and processing technology. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Resonant-cavity InGaN quantum-well blue light-emitting diodes

Y.-K. Song, M. Diagne, H. Zhou, A. V. Nurmikko, R. P. Schneider, and T. Takeuchi

Appl. Phys. Lett. 77, 1744 (2000); http://dx.doi.org/10.1063/1.1310625 (3 pages) | Cited 40 times

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We describe progress in blue resonant-cavity light-emitting diodes, based on InGaN/GaN quantum-well heterostructures. We have fabricated vertical-microcavity devices in which either one or both mirrors forming the cavity are patterned, high-reflectivity dielectrics Bragg reflectors. The results suggest that a blue vertical-cavity diode laser may be feasible by this approach. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.55.Sa Microcavity and microdisk lasers
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Thin-film-induced index change and channel waveguiding in epitaxial GaN films

Euisong Kim, Byounghee Lee, Ahmed Nahhas, and Hong Koo Kim

Appl. Phys. Lett. 77, 1747 (2000); http://dx.doi.org/10.1063/1.1311315 (3 pages) | Cited 7 times

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We report on optical waveguiding in the channel region of an epitaxial GaN film defined by a SiN cladding layer of a stripe window pattern. We carried out numerical analyses on the various possible effects that might contribute to the overcompensation of the negative loading effect of a SiN cladding window. This includes the photoelastic, piezoelectric, and electro-optic effects in GaN induced by a SiN window layer. The analysis result suggests that the observed phenomenon can be ascribed to a combination of both the photoelastic and electro-optic effects, and especially that the spontaneous polarization field in undoped GaN with a low background carrier concentration might play an important role in forming a channel waveguide in the window region. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.79.Gn Optical waveguides and couplers
77.65.Ly Strain-induced piezoelectric fields
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
78.20.Jq Electro-optical effects

High-brightness organic double-quantum-well electroluminescent devices

Jingsong Huang, Kaixia Yang, Shiyong Liu, and Hongjin Jiang

Appl. Phys. Lett. 77, 1750 (2000); http://dx.doi.org/10.1063/1.1311313 (3 pages) | Cited 25 times

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An organic double-quantum-well structure electroluminescent device fabricated by a doping method is demonstrated. The device consists of N,N′-bis-(1-naphthl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) used as a hole transporter, undoped tris(8-quinolinolato) aluminum (Alq) as a barrier potential or electron transporter, and Alq doped with 5,6,11,12-tetraphenylnaphthacene (rubrene) as a potential well and emitter, and has the following structure: indium tin oxide/NPB/Alq:rubrene/Alq/Alq:rubrene/Alq/Mg/Al. The maximum brightness and efficiency reach 48 000 cd/m2 and 4.59 lm/W, respectively. The present double-quantum-well structure device shows higher brightness and higher efficiency than those of the common heterostructure devices. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence

Nonlinear processes responsible for nondegenerate four-wave mixing in quantum-dot optical amplifiers

Tomoyuki Akiyama, Osamu Wada, Haruhiko Kuwatsuka, Takashi Simoyama, Yoshiaki Nakata, Kohki Mukai, Mitsuru Sugawara, and Hiroshi Ishikawa

Appl. Phys. Lett. 77, 1753 (2000); http://dx.doi.org/10.1063/1.1311319 (3 pages) | Cited 35 times

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Wavelength conversion using nondegenerate four-wave mixing in quantum-dot optical amplifiers is investigated. From the detuning frequency dependence of χ(3), derived from the conversion efficiency, we consider that, within the range of detuning in the experiment, spectral-hole burning and carrier heating are responsible, and that their time constants, i.e., carrier relaxation time to the ground state and the phonon scattering time, are in the range of 60–140 and 200–400 fs, respectively. This indicates that the carrier supply to the ground level via relaxation from the higher levels is very fast and that a broad conversion bandwidth comparable to that of quantum-well devices is ensured. © 2000 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.An Optical susceptibility, hyperpolarizability
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.55.Px Semiconductor lasers; laser diodes
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.66.Fd III-V semiconductors

Short-cavity, edge-emitting lasers with high-reflectance, dielectric mirrors

J. L. Fitz, S. C. Horst, D. S. Hinkel, and H. Turk

Appl. Phys. Lett. 77, 1756 (2000); http://dx.doi.org/10.1063/1.1311322 (3 pages) | Cited 1 time

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The fabrication and characterization of short-cavity, edge-emitting lasers operating at 861 nm is reported. These lasers were fabricated with high-reflectance, dielectric mirrors formed by plasma-enhanced, chemical-vapor deposition. Lasers with cavity lengths of 64 and 32 μm had continuous-wave, room-temperature threshold currents of 4.0 and 2.9 mA, respectively. To determine the reflectance of the deposited dielectric mirrors, a simple relationship was derived that used the change in the laser threshold current density resulting from mirror deposition.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Bh Lenses, prisms and mirrors
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Third-order nonlinear optical properties of an expanded porphyrin cadmium complex

Wenfang Sun, Clare C. Byeon, Chris M. Lawson, Gary M. Gray, and Duoyuan Wang

Appl. Phys. Lett. 77, 1759 (2000); http://dx.doi.org/10.1063/1.1311321 (3 pages) | Cited 13 times

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The third-order nonlinear optical properties of a pentaazadentate porphyrin-like cadmium complex, [(DBP–APPC)Cd]Cl, have been investigated using 40-ps and 5-ns laser pulses at 532 nm. The molecular second-order hyperpolarizability of this complex is 9.7×10−31 esu, and the nonlinearity is predominantly electronic in origin with picosecond laser pulses. Temporal response of the nonlinear process is composed of at least two components with different time responses and shows a strong fluence dependence that indicates the participation of excited states in the nonlinear process. Nonlinear absorption measurements demonstrate that this complex shows strong reverse saturable absorption for nanosecond laser pulses, but exhibits a transformation from reverse saturable absorption to saturable absorption at high fluence for picosecond pulses. These results suggest that [(DBP–APPC)Cd]Cl is a very promising candidate for optical limiting of nanosecond laser pulses. © 2000 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.An Optical susceptibility, hyperpolarizability
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Jk Polymers and organics

Differential electronic gating: A method to measure the shape of short THz pulses with a poorly defined trigger signal

J. N. Hovenier, R. W. van Es, T. O. Klaassen, W. Th. Wenckebach, M. Krätschmer, F. Klappenberger, E. Schomburg, S. Winnerl, G. M. H. Knippels, and A. F. G. van der Meer

Appl. Phys. Lett. 77, 1762 (2000); http://dx.doi.org/10.1063/1.1311601 (3 pages) | Cited 3 times

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A simple experimental method has been developed to determine the shape of repetitive picosecond THz pulses in the presence of a large jitter in the trigger signal. This method, a modification of the recently reported differential optical gating method, is based on the femtosecond electronic gating of a high-frequency sequential oscilloscope. As a test, the shape of THz pulses from the free-electron laser has been measured. © 2000 American Institute of Physics.
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42.79.Dj Gratings
41.60.Cr Free-electron lasers
42.60.Mi Dynamical laser instabilities; noisy laser behavior
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment

Optical properties of spontaneous lateral composition modulation in AlAs/InAs short-period superlattices

S. Francoeur, Yong Zhang, A. G. Norman, F. Alsina, A. Mascarenhas, J. L. Reno, E. D. Jones, S. R. Lee, and D. M. Follstaedt

Appl. Phys. Lett. 77, 1765 (2000); http://dx.doi.org/10.1063/1.1311598 (3 pages) | Cited 7 times

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The effect of lateral composition modulation, spontaneously generated during the epitaxial growth of an AlAs/InAs short-period superlattice, on the electronic band structure is investigated using phototransmission and photoluminescence spectroscopy. Compared with uniform layers of identical average composition, the presence of the composition modulation considerably reduces the band-gap energy and produces strongly polarized emission and absorption spectra. We demonstrate that the dominant polarization direction can selectively be aligned along the [math10] or [010] crystallographic directions. In compressively strained samples, the use of (001) InP substrates slightly miscut toward (111)A or (101) resulted in modulation directions along [110] or [100], respectively, and dominant polarization directions along a direction orthogonal to the respective composition modulation. Band-gap reductions as high as 350 and 310 meV are obtained for samples with composition modulation along [110] and [100], respectively. Ratios of polarized intensities up to 26 are observed in transmission spectra. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Micro-optomechanical sensor for optical connection in the near field

B. Belier, A. Santoso, J. Bonnafe, L. Nicu, P. Temple-Boyer, and C. Bergaud

Appl. Phys. Lett. 77, 1768 (2000); http://dx.doi.org/10.1063/1.1311602 (3 pages) | Cited 1 time

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A micro-optomechanical sensor has been used to collect and carry optical information at the nanometer scale. This simple device consists of a SiNx microfabricated cantilever used simultaneously as an atomic-force microscope (AFM) probe and optical waveguide. When approaching the micro-optical cantilever close to the surface, the tip converts evanescent waves into radiative waves that propagate within the cantilever over long distances. Since the device is also employed as an AFM probe, mechanical contact is fully controlled as the tip approaches the surface, thus avoiding any crash. This sensor has been used to collect optical information from an optical fiber in the near field. © 2000 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
07.79.Fc Near-field scanning optical microscopes
07.79.Lh Atomic force microscopes
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.81.Qb Fiber waveguides, couplers, and arrays

Chaos in an additive-pulse mode-locked laser

E. J. Mozdy and C. R. Pollock

Appl. Phys. Lett. 77, 1771 (2000); http://dx.doi.org/10.1063/1.1311816 (3 pages)

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We present and analyze an experimental bifurcation diagram for the additive-pulse modelocked (APM) laser, reconfirming the existence of both quasiperiodicity and period-doubling bifurcations into chaos for this system. Large fiber coupling is required to observe period doublings into chaos, while quasiperiodicity occurs for small fiber coupling. The experimental chaotic time series are reconstructed in phase space using the method of delayed coordinates, then graphically compared with the expected orbits from APM simulations. This experimental bifurcation diagram for the APM laser demonstrates that the main contribution to APM instability is in fact deterministic. © 2000 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.65.Sf Dynamics of nonlinear optical systems; optical instabilities, optical chaos and complexity, and optical spatio-temporal dynamics
42.55.Rz Doped-insulator lasers and other solid state lasers
05.45.Tp Time series analysis

Magneto-optical disk properties enhanced by a nonmagnetic mask layer

J. H. Kim, D. Buechel, T. Nakano, J. Tominaga, N. Atoda, H. Fuji, and Y. Yamakawa

Appl. Phys. Lett. 77, 1774 (2000); http://dx.doi.org/10.1063/1.1290489 (3 pages) | Cited 13 times

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Magneto-optical (MO) recording signals were enhanced by a nonmagnetic mask layer combining a silver oxide (AgOx) thin film and near-field coupled super-resolution. The signal intensity of 300 nm marks recorded by a 680 nm laser and a lens numerical aperture of 0.55 with light-intensity modulation was amplified 100 times in comparison with conventional MO media. Resolution of less than 200 nm was achieved by near-field coupling between a light-scattering center generated in the AgOx film and light polarization of MO marks. To identify near-field enhancement, we simulated electrical field components, finding that near-field coupling between the light-scattering center and a MO layer enhances MO signals about 20 times due to the surface plasmon effect. © 2000 American Institute of Physics.
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42.79.Vb Optical storage systems, optical disks
85.70.Sq Magnetooptical devices
42.30.Va Image forming and processing
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Determination of internal optical mode loss of semiconductor laser diodes

Linzhang Wu

Appl. Phys. Lett. 77, 1777 (2000); http://dx.doi.org/10.1063/1.1310208 (3 pages)

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This letter proposes a technique to accurately determine the internal optical mode loss of individual semiconductor laser diode for each given current, which is simple and based on measurements of spontaneous emission spectra. Therefore, it can be used to study the dependence of loss on temperature, current, and carrier density. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.50.Nn Quantum optical phenomena in absorbing, amplifying, dispersive and conducting media; cooperative phenomena in quantum optical systems
78.45.+h Stimulated emission
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Influence of electrode-size effects on plasma sheath expansion

Han S. Uhm, Gon H. Kim, Young W. Kim, Gun. W. Kim, Seung H. Han, and Mun P. Hong

Appl. Phys. Lett. 77, 1780 (2000); http://dx.doi.org/10.1063/1.1311318 (3 pages)

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Influence of the electrode-size effects on plasma sheath expansion is investigated for a negative voltage at the cathode with maximum amplitude of V0, assuming that the cathode is a thin, flat, conducting, circular disk of radius R. It is shown that propagation of the sheath front is proportional to the one-third power of the combination, 2V0R/π. Experimental measurements have been carried out to verify theoretical predictions. The experimental data agree remarkably well with theoretical results in every aspect. © 2000 American Institute of Physics.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
52.65.-y Plasma simulation
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Very thin insulating layer formed by low-energy Ar-beam bombardment in the surface region of undoped hydrogenated amorphous silicon

R. Durny, E. Pincik, V. Nadazdy, M. Jergel, J. Shimizu, M. Kumeda, and T. Shimizu

Appl. Phys. Lett. 77, 1783 (2000); http://dx.doi.org/10.1063/1.1310634 (3 pages) | Cited 5 times

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A very thin insulating layer (VTIL) is formed by low-energy Ar-beam bombardment in the surface region of undoped hydrogenated amorphous silicon (a-Si:H). Several experimental techniques have been utilized to determine the optimal argon beam bombardment conditions to prepare electrically reliable VTIL and to investigate its physical properties (thickness, structure, nature, and density of defects). VTILs prepared under such conditions make the leakage current of a-Si:H based semiconductor structures negligible and allow bias voltages of several volts (up to 5 V). © 2000 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Scanning reflection electron microscopy study of surface defects in GaN films formed by epitaxial lateral overgrowth

Heiji Watanabe, Naotaka Kuroda, Haruo Sunakawa, and Akira Usui

Appl. Phys. Lett. 77, 1786 (2000); http://dx.doi.org/10.1063/1.1310631 (3 pages) | Cited 4 times

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We have used scanning reflection electron microscopy (SREM) to detect surface defects in GaN films formed by facet-initiated epitaxial lateral overgrowth. SREM revealed individual threading dislocations and single atomic steps on the GaN surface, and provided images of crystallographic tilting near the surfaces. We found that one of the two tilted GaN crystals in the overgrown areas became dominant and that the surface changed to a single domain after 50-μm-thick GaN deposition. Our SREM results also showed that the deposition of thick (over 100 μm) GaN films significantly improves the crystallographic structures of the overgrown regions, and reduces the threading dislocations in the GaN films. © 2000 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Strain-induced material intermixing of InAs quantum dots in GaAs

M. O. Lipinski, H. Schuler, O. G. Schmidt, K. Eberl, and N. Y. Jin-Phillipp

Appl. Phys. Lett. 77, 1789 (2000); http://dx.doi.org/10.1063/1.1311314 (3 pages) | Cited 60 times

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A systematic investigation of the stacking behavior of InAs quantum dots (QDs) with varying GaAs interlayer thickness d is presented. We compare two-fold stacks of large QDs (≈25 nm base width), which emit at 1.30 μm, to small QDs (≈20 nm base width) emitting at 1.14 μm. For large islands photoluminescence yields an energetic blueshift of the second layer islands with decreasing d, although transmission electron microscopy clearly reveals a ≈70% larger dot size in the second layer, whereas for small islands a similar size increase of the dots in the upper layer and an energetic redshift are observed. A detailed analysis of confinement and material intermixing effects suggests that for large QDs strain driven material intermixing is dominant. For small QDs the confinement effect plays the major role and causes the observed photoluminescence energy redshifts. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
66.30.Ny Chemical interdiffusion; diffusion barriers

Characterizing mechanical resonators by means of a scanning acoustic force microscope

F. Sthal and R. Bourquin

Appl. Phys. Lett. 77, 1792 (2000); http://dx.doi.org/10.1063/1.1311317 (3 pages) | Cited 1 time

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A method of characterizing resonators is presented. This method is based on scanning acoustic force microscopy. Data on the topography and the vibration amplitude of the resonator are obtained simultaneously, by means of atomic force interaction. The normal component of the surface vibration of the resonator is evaluated. A tuning fork resonator and a 10 MHz SC-cut Boîtier Vieillissement Amélioré quartz crystal resonator with adherent electrodes are studied. This analysis allows the cartography of the local characteristics of the resonator material to be made. © 2000 American Institute of Physics.
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07.10.-h Mechanical instruments and equipment
07.79.Lh Atomic force microscopes
43.58.Ls Acoustical lenses and microscopes
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
43.35.Yb Ultrasonic instrumentation and measurement techniques

Plasma-induced damage to n-type GaN

H. W. Choi, S. J. Chua, A. Raman, J. S. Pan, and A. T. S. Wee

Appl. Phys. Lett. 77, 1795 (2000); http://dx.doi.org/10.1063/1.1311605 (3 pages) | Cited 34 times

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The effects of plasma etching on 1/f noise and photoluminescence (PL) characteristics of n-GaN have been investigated. A reduction of 1/f noise was observed after plasma exposure, a result of enhanced passivation of the reactive surface. This is attributed to the removal of carbon and the creation of a Ga-rich surface by the etching process. Nevertheless, the formation of nonradiative recombination centers impaired the PL intensity. Reconstruction of a stoichiometric surface was achieved by annealing. This induced the incorporation of carbon into GaN, deteriorating the PL performance further, but it could be restored by a chemical treatment of 10:1 HF:H2O. © 2000 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)

Detection of terahertz radiation from longitudinal optical phonon–plasmon coupling modes in InSb film using an ultrabroadband photoconductive antenna

Ping Gu, Masahiko Tani, Kiyomi Sakai, and T.-R. Yang

Appl. Phys. Lett. 77, 1798 (2000); http://dx.doi.org/10.1063/1.1311609 (3 pages) | Cited 13 times

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Terahertz radiation from longitudinal optical (LO) phonon–plasmon coupling modes in InSb films is observed using an ultrafast photoconductive antenna detector. We demonstrate a response frequency of up to 7 THz for a low-temperature-grown GaAs-based photoconductive antenna gated with 25 fs laser pulses. It is found that the emission frequencies of the coupling modes are dependent only on the residual carrier density, not on the excitation carrier density. It is also found that the LO phonon–plasmon oscillations in semiconductors can serve as an efficient THz source. © 2000 American Institute of Physics.
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63.20.kk Phonon interactions with other quasiparticles
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
84.40.Ba Antennas: theory, components and accessories
72.30.+q High-frequency effects; plasma effects
72.80.Ey III-V and II-VI semiconductors

Uniaxial locked epitaxy of ZnO on the a face of sapphire

P. Fons, K. Iwata, A. Yamada, K. Matsubara, S. Niki, K. Nakahara, T. Tanabe, and H. Takasu

Appl. Phys. Lett. 77, 1801 (2000); http://dx.doi.org/10.1063/1.1311603 (3 pages) | Cited 81 times

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High-quality, c-oriented ZnO epitaxial films have been grown on the a surface using molecular-beam epitaxy. The use of a-oriented sapphire eliminates rotational domains and related structural defects which have limited the use of ZnO in electronic applications. The ZnO epitaxial layers are uniquely oriented with the ZnO/sapphire orientational relationship [0001]‖[11math0] and 〈11math0〉‖[0001]. This unique orientation is a consequence of the anisotropy of the a-sapphire surface in conjunction with a strong correlation along a single direction leading to the term uniaxial locked epitaxy. High-resolution x-ray diffraction measurements show an increase in x-ray lateral coherence length from several tens of nanometers to >0.7 μm for growth of c-oriented ZnO on the a surface as opposed to the c surface of sapphire. © 2000 American Institute of Physics.
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81.05.Dz II-VI semiconductors
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Two-step growth of high-quality GaN by hydride vapor-phase epitaxy

P. R. Tavernier, E. V. Etzkorn, Y. Wang, and D. R. Clarke

Appl. Phys. Lett. 77, 1804 (2000); http://dx.doi.org/10.1063/1.1311600 (3 pages) | Cited 20 times

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The use of a low-temperature layer of GaN formed by hydride vapor-phase epitaxy (HVPE) as a template to grow high-quality HVPE films is demonstrated. Using layers formed by reacting GaCl and NH3 at 550 °C and annealed at a growth temperature of 1050 °C, thick films of GaN can be grown by HVPE with fewer than 108 dislocations per cm2. Dislocation densities measured by high-resolution x-ray diffraction, atomic-force microscopy step termination density and plan-view transmission electron miscroscopy reveal that ∼ 23 μm films have dislocation densities of ∼ 6×107 cm−2. Obtaining high-quality single-crystal character films was found to be dependent on several factors, most importantly, the rate of temperature increase to growth temperature and the layer thickness. © 2000 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Aligned CNx nanotubes by pyrolysis of ferrocene/C60 under NH3 atmosphere

Wei-Qiang Han, Philipp Kohler-Redlich, Torsten Seeger, Frank Ernst, Manfred Rühle, Nicole Grobert, Wen-Kuang Hsu, Bao-He Chang, Yan-Qiu Zhu, Harold W. Kroto, David R. M. Walton, Mauricio Terrones, and Humberto Terrones

Appl. Phys. Lett. 77, 1807 (2000); http://dx.doi.org/10.1063/1.1311813 (3 pages) | Cited 42 times

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Aligned CNx (x<0.1) nanotubes have been generated by pyrolyzing ferrocene/C60 mixtures at 1050 °C in an ammonia atmosphere. The structure and composition of the product were determined by high-resolution transmission electron microscopy and high spatial resolution electron energy-loss spectroscopy. The CNx tubes (15–70 nm diameter, <50 μm length) grown in large flakes (<3 mm2) consist of a reduced number of “graphitic” layers (<15 on either side) arranged in a bamboo-like structure. Areas of high nitrogen concentration were found within curved or corrugated “graphite-like” domains. The observation of a well-developed double peak in the σ∗ feature of the N K-edge suggests that the material has not undergone the transition to the fullerene-like phase known for nitrogenated carbons. Incorporation of nitrogen from the gas phase (NH3) into CNx nanotubes therefore leads to improved and more efficient N substitution into the network as compared to the synthesis with solid nitrogen-containing precursors reported earlier. © 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
81.05.Cy Elemental semiconductors
79.20.Kz Other electron-impact emission phenomena
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Determination of thermal conductivity of natural silicate melts

R. Büttner, B. Zimanowski, C. Lenk, A. Koopmann, and V. Lorenz

Appl. Phys. Lett. 77, 1810 (2000); http://dx.doi.org/10.1063/1.1311815 (3 pages) | Cited 8 times

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Cooling of natural silicate melts and energy transfer to the environment are controlled by the temperature-dependent thermal conductivity. We describe a method that allows a correlation between temperature-dependent strain rate and a bulk temperature during a cooling or heating process under quasisteady state conditions in a Newtonian flow regime. A rotational viscometer measured data for experimental cooling curves of remelted volcanic rock materials. From these data we can calculate the thermal conductivity of an unknown melt after we calibrate the setup with a melt of known thermal conductivity as a by-product of viscosimetry. © 2000 American Institute of Physics.
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93.85.-q Instruments and techniques for geophysical research: Exploration geophysics
91.60.Ki Thermal properties
83.80.Nb Geological materials: Earth, magma, ice, rocks, etc.
07.20.-n Thermal instruments and apparatus
66.25.+g Thermal conduction in nonmetallic liquids
83.85.Jn Viscosity measurements

Phonons and exciton recombination in CdSe/ZnSe self-assembled quantum dots

H. Rho, L. M. Robinson, L. M. Smith, Howard E. Jackson, S. Lee, M. Dobrowolska, and J. K. Furdyna

Appl. Phys. Lett. 77, 1813 (2000); http://dx.doi.org/10.1063/1.1311393 (3 pages) | Cited 13 times

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We report resonant photoluminescence from CdSe/ZnSe self-assembled quantum dots. When CdSe quantum dots are resonantly excited, excitonic sharp micro-photoluminescence peaks originating from individual quantum dots are strongly enhanced in the region corresponding to optical phonon energies below the excitation. The phonons active in this process are identified as the longitudinal optical (LO) phonons from the CdSe dots, as the interface phonons, and tentatively as the LO phonons from the two-dimensional-like precursor layers. These observations suggest that exciton recombination via phonons is a major relaxation process under resonant excitation. © 2000 American Institute of Physics.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
63.20.kk Phonon interactions with other quasiparticles
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
68.35.Ja Surface and interface dynamics and vibrations
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.Gg Exciton-mediated interactions
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