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24 Apr 2000

Volume 76, Issue 17, pp. 2325-2474

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Self-organized formation and photoluminescence of Cd1−xMnxTe quantum dots grown on ZnTe by atomic layer epitaxy

Yoshikazu Terai, Shinji Kuroda, and Kôki Takita

Appl. Phys. Lett. 76, 2400 (2000); http://dx.doi.org/10.1063/1.126357 (3 pages) | Cited 14 times

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Self-organized quantum dots (QDs) of Cd1−xMnxTe were grown on the ZnTe(100) surface by atomic layer epitaxy. Atomic force microscope measurement on the surface of a 3.5-ML-thick Cd1−xMnxTe layer revealed dot formation in a high density of the order of 1010–1011 cm−2 when the Mn composition x was less than 10%. The typical dot size was given approximately by 20 nm in diameter and 2 nm in height. In photoluminescence (PL) measurements on the capped QDs, the excitonic emissions from the QDs were observed at 2.16–2.27 eV in the range of Mn composition x = 0%–10%. The PL spectra from Cd1−xMnxTe QDs with x = 0.6%–10.2% consisted of two lines separated by about 20 meV. The dependence of the PL energies on the Mn composition and the Zeeman shift were compared with the calculation. © 2000 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
75.50.Pp Magnetic semiconductors
81.05.Dz II-VI semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Ls Magneto-optical effects

Selective enhancement of 1540 nm Er3+ emission centers in Er-implanted GaN by Mg codoping

S. Kim, S. J. Rhee, X. Li, J. J. Coleman, and S. G. Bishop

Appl. Phys. Lett. 76, 2403 (2000); http://dx.doi.org/10.1063/1.126358 (3 pages) | Cited 36 times

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The ∼1540 nm 4I13/2 to 4I15/2 Er3+ photoluminescence (PL) and photoluminescence excitation (PLE) spectra of Er-implanted Mg-doped GaN reveal a selective enhancement of one of the nine different Er3+ centers observed previously in PL and PLE studies of Er-implanted undoped GaN. These Er3+ PL spectra are excited selectively by pump wavelengths that correspond to broadband, below-gap absorption bands associated with different Er3+ centers. In the Er-implanted, Mg-doped GaN, both the 1540 nm PL spectrum characteristic of the so-called violet-pumped Er3+ center and the ∼2.8–3.4 eV (violet) PLE band that enables its selective excitation are significantly enhanced by Mg doping. In addition, the violet-pumped PL center dominates the above-gap-excited Er3+ PL spectrum of Er-implanted Mg-doped GaN, whereas it was nearly unobserveable under above-gap excitation in Er-implanted undoped GaN. These results confirm our hypothesis that appropriate codopants can increase the efficiency of trap-mediated above-gap excitation of Er3+ emission in Er-implanted GaN. © 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
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Photoexcited carrier transfer in InGaAs quantum dot structures: Dependence on the dot density

Saulius Marcinkevicius and Rosa Leon

Appl. Phys. Lett. 76, 2406 (2000); http://dx.doi.org/10.1063/1.126359 (3 pages) | Cited 23 times

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Carrier dynamics has been measured by time-resolved photoluminescence in self-assembled InGaAs/GaAs quantum-dot structures with dot density of the order of 108–1010 cm−2. The time of carrier transfer into a dot, which ranges from 2 to 20 ps, has been found to decrease with increasing quantum dot density. The temperature and photoexcited carrier density dependencies of the carrier transfer times suggest that potential barriers at wetting layer and quantum-dot interfaces hinder carrier capture in low-density quantum-dot structures. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Dn Low-field transport and mobility; piezoresistance
78.47.-p Spectroscopy of solid state dynamics
73.50.Pz Photoconduction and photovoltaic effects

Large, nitrogen-induced increase of the electron effective mass in InyGa1−yNxAs1−x

C. Skierbiszewski, P. Perlin, P. Wisniewski, W. Knap, T. Suski, W. Walukiewicz, W. Shan, K. M. Yu, J. W. Ager, E. E. Haller, J. F. Geisz, and J. M. Olson

Appl. Phys. Lett. 76, 2409 (2000); http://dx.doi.org/10.1063/1.126360 (3 pages) | Cited 147 times

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A dramatic increase of the conduction band electron mass in a nitrogen-containing III–V alloy is reported. The mass is found to be strongly dependent on the nitrogen content and the electron concentration with a value as large as 0.4m0 in In0.08Ga0.92As0.967N0.033 with 6×1019 cm−3 free electrons. This mass is more than five times larger than the electron effective mass in GaAs and comparable to typical heavy hole masses in III–V compounds. The results provide a critical test and fully confirm the predictions of the recently proposed band anticrossing model of the electronic structure of the III–N–V alloys. © 2000 American Institute of Physics.
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71.20.Nr Semiconductor compounds
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Gating individual nanotubes and crosses with scanning probes

Thomas W. Tombler, Chongwu Zhou, Jing Kong, and Hongjie Dai

Appl. Phys. Lett. 76, 2412 (2000); http://dx.doi.org/10.1063/1.125611 (3 pages) | Cited 21 times

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Atomic force microscopy tips are used to apply point-like local gates to manipulate the electrical properties of individual single-walled carbon nanotubes (SWNT) contacted by Ti electrodes. Depleting a semiconducting SWNT at a local point along its length leads to orders of magnitude decrease of the nanotube conductance, whereas local gating to metallic SWNTs causes no change in the conductance of the system. These results shed light into gating effects on metal-tube contacts. Electrical properties of SWNT crosses are also investigated. Scanning-probe gating is used to identify the metallic or semiconducting nature of the nanotube components in the crosses. © 2000 American Institute of Physics.
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73.61.Wp Fullerenes and related materials
85.40.Ls Metallization, contacts, interconnects; device isolation
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Spatial instability of the nonlinear ferromagnetic resonance in uniaxial films

A. F. Popkov, T. Wöbbeking, H. Dötsch, and V. I. Korneev

Appl. Phys. Lett. 76, 2415 (2000); http://dx.doi.org/10.1063/1.126361 (3 pages) | Cited 1 time

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The spatial instability of the nonlinear magnetization precession in uniaxial films with low magnetization is analyzed analytically and numerically solving Landau–Lifshitz equations. The foldover effect is essential in this geometry. The formation of spatial soliton-like magnetization precessions is predicted for nonuniform driving inductions exceeding the threshold value. Time–space instability boundaries of the obtained soliton-like structures are calculated. The numerical simulations show that these structures are stabilized at the boundaries of the foldover region. This behavior is in qualitative agreement with a recent experiment where a spatial pattern formation by a nonuniformly driven ferromagnetic resonance in a garnet film has been observed. © 2000 American Institute of Physics.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.70.Ak Magnetic properties of monolayers and thin films
05.45.Yv Solitons
75.30.Ds Spin waves

Barkhausen jumps in a magnetic microstructure

Ezio Puppin, Simona Ricci, and Luca Callegaro

Appl. Phys. Lett. 76, 2418 (2000); http://dx.doi.org/10.1063/1.126362 (3 pages) | Cited 7 times

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The magnetization process in a square dot of permalloy having a size of 20 μm and 80 nm thickness has been investigated with a focused magneto-optical hysteresigraph. With this apparatus, it is possible to measure in a few seconds the hysteresis loop with a signal-to-noise ratio adequate for the observation of Barkhausen jumps also in such a small magnetic sample. From a sequence of 6000 loops, systematic data on the statistical properties of these jumps have been extracted. The observed behavior shows strong deviations with respect to the available data on bulk samples and thin films. © 2000 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
78.66.Bz Metals and metallic alloys

Strain-dependent magnetic phase diagram of epitaxial La0.67Sr0.33MnO3 thin films

F. Tsui, M. C. Smoak, T. K. Nath, and C. B. Eom

Appl. Phys. Lett. 76, 2421 (2000); http://dx.doi.org/10.1063/1.126363 (3 pages) | Cited 116 times

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Effects of lattice strain on magnetic behavior of epitaxial La0.67Sr0.33MnO3 thin films grown by 90° off-axis sputtering have been studied. The size of epitaxial strain was varied using four different substrates, i.e., (001) LaAlO3, (001) SrTiO3, (001) La0.3Sr0.7Al0.65Ta0.35O9, and (110) NdGaO3. The observed magnetism of coherent epitaxial films grown on these substrates, particularly anisotropy and Curie temperature, exhibit strong correlations with lattice strains. Spin reorientation transitions have been observed. The dependence of Curie temperature on the bulk and Jahn–Teller strains has been determined. © 2000 American Institute of Physics.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
75.50.Dd Nonmetallic ferromagnetic materials
68.60.Bs Mechanical and acoustical properties
81.15.Cd Deposition by sputtering
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.Gk Colossal magnetoresistance

Low resistance and high thermal stability of spin-dependent tunnel junctions with synthetic antiferromagnetic CoFe/Ru/CoFe pinned layers

J. J. Sun, K. Shimazawa, N. Kasahara, K. Sato, S. Saruki, T. Kagami, O. Redon, S. Araki, H. Morita, and M. Matsuzaki

Appl. Phys. Lett. 76, 2424 (2000); http://dx.doi.org/10.1063/1.126364 (3 pages) | Cited 45 times

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In this work, submicron-size (down to 0.273 μm2) spin–dependent tunnel junctions with resistance as low as ∼30 Ω μm2 have been fabricated, where the tunneling barrier of AlOx was formed by in situ natural oxidation. These junctions annealed at 250 °C for 5 h showed tunneling magnetoresistance (TMR) of 14.3% and 25.8% for the pinned layers of CoFe/RuRhMn and CoFe/PtMn, respectively, while the TMR is further increased to 31.6% for a synthetic antiferromagnetic pinned layer of CoFe/Ru/CoFe/PtMn due to less interdiffusion at CoFe/Ru interface. The investigation has indicated that the growth of ultrathin Al layer is very sensitive to the surface roughness of bottom ferromagnetic electrode, and large surface roughness leads to small junction resistance. © 2000 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.45.+j Macroscopic quantum phenomena in magnetic systems
73.40.Jn Metal-to-metal contacts
75.50.Ee Antiferromagnetics
72.15.Gd Galvanomagnetic and other magnetotransport effects
68.60.Dv Thermal stability; thermal effects
68.35.Fx Diffusion; interface formation
68.35.B- Structure of clean surfaces (and surface reconstruction)

Nucleation of epitaxial yttria-stabilized zirconia on biaxially textured (001) Ni for deposited conductors

C. Park, D. P. Norton, D. T. Verebelyi, D. K. Christen, J. D. Budai, D. F. Lee, and A. Goyal

Appl. Phys. Lett. 76, 2427 (2000); http://dx.doi.org/10.1063/1.126365 (3 pages) | Cited 15 times

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The nucleation of (001)-oriented yttria-stabilized zirconia (YSZ) directly on the (001) Ni surface is realized via nucleation on an oxygen-terminated nickel surface using pulsed-laser deposition. Under conditions where the nickel surface is either oxygen free or substantially covered with NiO, a mixed orientation of YSZ occurs. The epitaxial YSZ layer grown on a biaxially textured Ni(001) surface was used as a single buffer layer for a high temperature superconducting coated conductor architecture, yielding superconducting YBa2Cu3O7 films with high critical current densities, Jc. This architecture eliminates the necessity for a multilayer buffer architecture, since high Jc superconducting films are achieved with no intermediate buffer layer between the (001) YSZ and the biaxially textured metal. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
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SrRuO3/(Ba, Sr)TiO3/SrRuO3 capacitor annealed in the forming gas with and without oxygen addition

Jun Lin, Katsuaki Natori, Yoshiaki Fukuzumi, Mitsuaki Izuha, Kohji Tsunoda, Kazuhiro Eguchi, Katsuhiko Hieda, and Daisuke Matsunaga

Appl. Phys. Lett. 76, 2430 (2000); http://dx.doi.org/10.1063/1.126366 (3 pages) | Cited 9 times

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Forming gas (3%H2+97%N2) anneals result in decomposition of SrRuO3 and increase the leakage current of the SrRuO3/(Ba, Sr)TiO3/SrRuO3 capacitor. However, we show that 0.5% O2 addition to the forming gas (3%H2+0.5%O2+96.5%N2) does not cause degradation of the SrRuO3/(Ba, Sr)TiO3/SrRuO3 capacitor, and can also enhance the performance of the transistor effectively. To correctly study the effect of a forming gas anneal on the SrRuO3/(Ba, Sr)TiO3/SrRuO3 capacitor, efforts should be made to avoid the possible O2 diffusion from air into furnace. © 2000 American Institute of Physics.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.80.-e Ferroelectricity and antiferroelectricity
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.65.-b Surface treatments

Effects of the postannealing atmosphere on the dielectric properties of (Ba, Sr)TiO3 capacitors: Evidence of an interfacial space charge layer

F. M. Pontes, E. R. Leite, E. Longo, J. A. Varela, E. B. Araujo, and J. A. Eiras

Appl. Phys. Lett. 76, 2433 (2000); http://dx.doi.org/10.1063/1.126367 (3 pages) | Cited 71 times

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The dielectric properties of (Ba, Sr)TiO3 films were found to be remarkably sensitive to the postannealing treatment atmosphere. This study demonstrates that postannealing in an oxygen atmosphere increases the dielectric relaxation phenomenon and that postannealing in a nitrogen atmosphere produces a slight dielectric relaxation. Such dependence of the dielectric relaxation was related both to oxygen vacancies and to the presence of negatively charged oxygen, trapped at the grain boundary and/or at the electrode/dielectric film interface. © 2000 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
77.22.Jp Dielectric breakdown and space-charge effects
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
77.80.Dj Domain structure; hysteresis

Ferroelectric domain reversal in congruent LiTaO3 crystals at elevated temperatures

Charles C. Battle, Sungwon Kim, Venkatraman Gopalan, Kendra Barkocy, Mool C. Gupta, Q. X. Jia, and T. E. Mitchell

Appl. Phys. Lett. 76, 2436 (2000); http://dx.doi.org/10.1063/1.126368 (3 pages) | Cited 10 times

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We report a four-times decrease in the electric fields for 180° domain reversal in congruent LiTaO3 crystals with an increase in temperature from 22 to 250 °C. This is accompanied by a substantial broadening of the field range over which domain reversal takes place, by an order of magnitude. The large internal fields of ∼5.5 kV/mm at room temperature, as measured by the asymmetry in polarization hysteresis loop, disappears at higher temperatures. With increasing temperature, the domain switching changes from lateral growth dominated to nucleation dominated kinetics. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
77.22.Ej Polarization and depolarization

Growth mode mapping of SrTiO3 epitaxy

M. Lippmaa, N. Nakagawa, M. Kawasaki, S. Ohashi, and H. Koinuma

Appl. Phys. Lett. 76, 2439 (2000); http://dx.doi.org/10.1063/1.126369 (3 pages) | Cited 46 times

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We have mapped the growth mode of homoepitaxial SrTiO3 thin films as a function of deposition rate and substrate temperature during pulsed laser deposition. The transition from layer by layer growth to step flow growth was mapped by making 260 depositions, 3 monolayers each, on a single substrate. The growth mode was determined by time-resolved reflection high-energy electron diffraction. An atomically smooth surface was regenerated after each deposition by annealing the sample at temperatures above 1200 °C. The depositions were performed at an oxygen pressure of 10−6 Torr and covered a temperature range from 900 to 1380 °C. The effective activation energies of surface migration on Ti- and Sr-terminated surfaces were determined from the mapping results. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Fg Pulsed laser ablation deposition
77.55.-g Dielectric thin films
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Threshold voltage of excimer-laser-annealed polycrystalline silicon thin-film transistors

C. T. Angelis, C. A. Dimitriadis, F. V. Farmakis, J. Brini, G. Kamarinos, and M. Miyasaka

Appl. Phys. Lett. 76, 2442 (2000); http://dx.doi.org/10.1063/1.126370 (3 pages) | Cited 8 times

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Based on experimental studies of n-channel excimer-laser-annealed polycrystalline silicon thin-film transistors with gate ratio width/length varying from 0.5 to 2.5, we propose a reliable method to determine the threshold voltage Vt from linear extrapolation of the transconductance to zero. The results reveal that the determined values of Vt are independent of the device geometry and the applied drain voltage in the linear region, in contrast with the drain current linear extrapolation method. The values of Vt are correlated with the density of the total trap states derived from the subthreshold gate swing voltage. © 2000 American Institute of Physics.
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85.30.Tv Field effect devices
81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

High-Tc gradiometric superconducting quantum interference device and its incorporation into a single-layer gradiometer

A. J. Millar, E. J. Romans, C. Carr, A. Eulenburg, G. B. Donaldson, P. Maas, and C. M. Pegrum

Appl. Phys. Lett. 76, 2445 (2000); http://dx.doi.org/10.1063/1.126371 (3 pages) | Cited 7 times

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We describe a first-order gradiometric dc superconducting quantum interference device (SQUID) and its incorporation into a first-order directly coupled single-layer gradiometer. The gradiometric SQUIDs were fabricated from a single layer of YBa2Cu3O7, with a silicon dioxide insulating layer and a gold crossover structure. For several gradiometric SQUIDs, with estimated inductances of order 67 pH, we measured parasitic effective areas in the range 1–2 μm2, approximately two orders of magnitude lower than for conventional narrow linewidth SQUIDs of similar inductance. For a single-layer gradiometer incorporating a gradiometric SQUID, we measured a parasitic effective area of 95 μm2. We demonstrate that for this device, the SQUID itself makes a negligible contribution to the overall parasitic effective area. We show that the improved balance leads to better performance in an unshielded environment. © 2000 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Hydrogenation of ZnS passivation on narrow-band gap HgCdTe

J. K. White, C. A. Musca, H. C. Lee, and L. Faraone

Appl. Phys. Lett. 76, 2448 (2000); http://dx.doi.org/10.1063/1.126372 (3 pages) | Cited 12 times

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Due to the narrow band gap of HgCdTe required for infrared photodetectors, the device performance is readily influenced by surface effects. This letter examines the effect that hydrogenation has on the quality of industry-standard ZnS passivating films. The hydrogenation is achieved by exposing the samples to a H2/CH4 plasma that is present during a reactive ion etching process. The results show a marked improvement of the passivant/substrate interface for hydrogenated devices with a reduction of the average fixed interface charge density to 3.5×1010 cm−2, accompanied by a sixfold decrease in the standard deviation. The advantage of this method of hydrogenation is that it is integrated into the reactive ion etch processing for mesa formation or p-type to n-type conversion in photoconductive or photovoltaic device fabrication, respectively. With the improvement of the ZnS passivation with hydrogenation, this method may alleviate the need for complex epitaxial passivation processing. © 2000 American Institute of Physics.
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81.65.Rv Passivation
81.05.Dz II-VI semiconductors
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
85.60.Gz Photodetectors (including infrared and CCD detectors)
81.65.Cf Surface cleaning, etching, patterning
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Peltier microcalorimeter

I. K. Moon, D. H. Jung, K.-B. Lee, and Y. H. Jeong

Appl. Phys. Lett. 76, 2451 (2000); http://dx.doi.org/10.1063/1.126373 (3 pages) | Cited 6 times

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We developed an ac microcalorimeter utilizing the Peltier effect of a thermocouple junction as an ac power source. This Peltier microcalorimeter allows us to measure the absolute value of the heat capacity of small samples with submilligrams of mass. The performance of the microcalorimeter was checked in the temperature range of 15–420 K with α-Al2O3 samples of 0.54 and 2.25 mg. The absolute accuracy was ±3% for the range of 30–150 K and ±1% for 150–420 K. The precision was better than 0.5% in the whole temperature range. © 2000 American Institute of Physics.
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07.20.Fw Calorimeters
65.40.-b Thermal properties of crystalline solids
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Improving the performance of conjugated polymer-based devices by control of interchain interactions and polymer film morphology

Thuc-Quyen Nguyen, Raymond C. Kwong, Mark E. Thompson, and Benjamin J. Schwartz

Appl. Phys. Lett. 76, 2454 (2000); http://dx.doi.org/10.1063/1.126374 (3 pages) | Cited 90 times

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Interchain interactions in conjugated polymer films promote good carrier transport but also reduce the luminescence quantum yield, leading to a fundamental trade-off in optimizing film morphology for device performance. We present two methods to improve the efficiency of light-emitting diodes (LEDs) based on poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) by altering film morphology without changing device architecture. First, “trilayer” LEDs, which use a central MEH-PPV layer with reduced interchain interactions between layers of highly aggregated MEH-PPV near the electrodes, have a higher efficiency than single-layer devices. Second, device efficiency can be improved by annealing MEH-PPV films, so that the reduced emission upon increasing interchain interactions is overcome by more balanced charge injection. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
61.41.+e Polymers, elastomers, and plastics
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials

High voltage operation (>80 V) of GaN bipolar junction transistors with low leakage

J. B. Limb, H. Xing, B. Moran, L. McCarthy, S. P. DenBaars, and U. K. Mishra

Appl. Phys. Lett. 76, 2457 (2000); http://dx.doi.org/10.1063/1.126375 (3 pages) | Cited 16 times

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We have demonstrated the high voltage operation of n-p-n GaN bipolar junction transistors using regrown emitters. Devices were grown by metalorganic chemical vapor deposition on sapphire substrates. The n-type emitter was grown selectively on a base-collector p-n junction diode using a dielectric mask. A thin base (1000 Å) was used to increase the current gain over our previous result with a regrown emitter [J. B. Limb, L. McCarthy, P. Kozodoy, H. Xing, J. Ibbetson, Y. Smorchkova, S. P. DenBaars, and U. K. Mishra, Electron. Lett. 35, 19 (1999)]. The base contacts were better than expected despite the use of a thin base. Common emitter operation showing a voltage operation of over 80 V with negligible leakage has been demonstrated. Room temperature current gain was ∼3 corresponding to a current transfer ratio of ∼0.75. This results in a calculated minority carrier lifetime of about 80 pS in the base. © 2000 American Institute of Physics.
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85.30.Pq Bipolar transistors
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
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Temperature measurements of a thermal wave at static high pressures

G. I. Pangilinan, H. D. Ladouceur, and T. P. Russell

Appl. Phys. Lett. 76, 2460 (2000); http://dx.doi.org/10.1063/1.126376 (3 pages) | Cited 1 time

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Experiments probing the dynamics of a thermal wave in a material compressed at static high pressures are presented. The method involves launching a thermal wave in a sample compressed in an anvil cell and monitoring the temporal profile of temperature at a fixed point downstream. A pulsed laser incident on a metal foil provides the thermal wave, while fluorescence from a small ruby sphere yields the time-resolved temperature. Results from compressed NaCl show that temperature rises quickly and decays much more slowly, consistent with the expected heat flow. This temporal profile evaluated with a numerical solution of the heat-conduction equation or an analytical approximation provides values for thermal conductivity, thermal diffusivity, and heat capacity at pressures to 1.7 GPa. © 2000 American Institute of Physics.
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07.20.Dt Thermometers
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.47.-p Spectroscopy of solid state dynamics
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
65.40.-b Thermal properties of crystalline solids
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
44.10.+i Heat conduction
62.50.-p High-pressure effects in solids and liquids

Physical origin of nonlinearity in the Fowler–Nordheim plot of field-induced emission from amorphous diamond films: Thermionic emission to field emission

N. S. Xu, Jun Chen, and S. Z. Deng

Appl. Phys. Lett. 76, 2463 (2000); http://dx.doi.org/10.1063/1.126377 (3 pages) | Cited 37 times

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Nonlinearity is observed in Fowler–Nordheim (FN) plots of field emission from nondoped and nitrogen-doped amorphous diamond films. Based on a unified electron emission equation a detailed analysis is carried out. The results from numerical calculation of the unified equation are consistent with the experimental data. It is shown that the nonlinearity in the FN plot originates from a transition from thermionic emission to field emission as the applied field increases. The electrical field ranges are derived in which the field emission and thermionic emission approximation applies. © 2000 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
79.40.+z Thermionic emission
81.05.ub Fullerenes and related materials
73.50.-h Electronic transport phenomena in thin films
73.61.-r Electrical properties of specific thin films

Low-energy electron-beam patterning of amine-functionalized self-assembled monolayers

C. K. Harnett, K. M. Satyalakshmi, and H. G. Craighead

Appl. Phys. Lett. 76, 2466 (2000); http://dx.doi.org/10.1063/1.126378 (3 pages) | Cited 48 times

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Patterned amine-functionalized self-assembled monolayers have potential as a template for the deposition and patterning of a wide variety of materials on silicon surfaces, including biomolecules. Results are presented here for low-energy electron-beam patterning of 2-aminopropyltriethoxysilane and (aminoethylaminomethyl)phenethyltrimethoxysilane self-assembled monolayers on silicon substrates. On these ultrathin (1–2 nm) monolayers, lower electron beam energies (<5 keV) produce higher resolution patterns than high-energy beams. Auger electron spectroscopy indicates that low-energy electron exposure primarily damages the amine groups. At 1 keV, a dose of 40 μC/cm2 is required to make the patterns observable by lateral force microscopy. Features as small as 80 nm were exposed at 2 keV on these monolayers. After exposure, palladium colloids and aldehyde- and protein-coated polystyrene fluorescent spheres adhered only to unexposed areas of the monolayers. © 2000 American Institute of Physics.
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68.18.-g Langmuir-Blodgett films on liquids
85.40.Hp Lithography, masks and pattern transfer
79.20.Fv Electron impact: Auger emission

Field emission of different oriented carbon nanotubes

Yan Chen, David T. Shaw, and Liping Guo

Appl. Phys. Lett. 76, 2469 (2000); http://dx.doi.org/10.1063/1.126379 (3 pages) | Cited 135 times

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Field emission data from aligned high-density carbon nanotubes (CNTs) with orientations parallel, 45°, and perpendicular to the substrate have been obtained. The large-area uniformly distributed CNTs were synthesized on smooth nickel substrates via dc plasma-assisted hot filament chemical vapor deposition. CNTs with diameters in the range of 100–200 nm were employed in this study. The different orientations were obtained by changing the angle between the substrate and the electrical field direction. The growth mechanism for the alignment and orientation control of CNTs has been discussed. The CNTs oriented parallel to the substrate have a lower onset applied field than those oriented perpendicular to the substrate. This result indicates that electrons can emit from the body of the CNT, which means that the CNT can be used as a linear emitter. The small radius of the tube wall and the existence of defects are suggested as the reasons for the emission of electrons from the body of the tubes. © 2000 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.05.ub Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Sono implantation of hydrogen and deuterium from water into metallic fine powders

Yoshiaki Arata and Yue-Chang Zhang

Appl. Phys. Lett. 76, 2472 (2000); http://dx.doi.org/10.1063/1.126380 (3 pages) | Cited 1 time

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We observed the production of hydrogenated/deuterated metallic fine powders when various metals (Pd, Ag, Ta, Pt, and Au) were irradiated in normal and heavy water by ultrasonic waves. Mass analyses of remnant metal powders revealed substantial amounts of sono-implanted hydrogen and deuterium. The deuterium implantation (D implantation) in D2O was found to be much stronger than the hydrogen implantation (H implantation) in H2O. © 2000 American Institute of Physics.
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43.35.Ty Other physical effects of sound
62.65.+k Acoustical properties of solids
61.72.up Other materials
61.82.Bg Metals and alloys
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
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