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7 Aug 2000

Volume 77, Issue 6, pp. 767-915

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Lateral epitaxial overgrowth of GaSb on GaSb and GaAs substrates by metalorganic chemical vapor deposition

S. S. Yi, D. M. Hansen, C. K. Inoki, D. L. Harris, T. S. Kuan, and T. F. Kuech

Appl. Phys. Lett. 77, 842 (2000); http://dx.doi.org/10.1063/1.1306919 (3 pages) | Cited 5 times

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Lateral epitaxial overgrowth of GaSb on GaSb and GaAs substrates patterned with SiO2 or Si3N4 films by metalorganic chemical vapor deposition was accomplished using trimethylgallium and trimethylantimony. Transmission electron microscopy measurements show that coalesced films grown on GaSb substrates exhibit defect-free materials, while those on GaAs substrates show regular, small-angle crystal tilting originating from large lattice mismatch. © 2000 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Reactive removal of misfit dislocations from InGaAs on GaAs by lateral oxidation

S. K. Mathis, P. Chavarkar, A. M. Andrews, U. K. Mishra, and J. S. Speck

Appl. Phys. Lett. 77, 845 (2000); http://dx.doi.org/10.1063/1.1306918 (3 pages)

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Layers of hypercritical thickness InGaAs/AlAs/GaAs have been shown to strain relax when the underlying AlAs layer is laterally oxidized. InxGa1−xAs layers of composition 0.2 ⩽ x ⩽ 0.4 have been investigated at thicknesses in the range 5–20 times the Matthews–Blakeslee critical thickness hc. The amount of strain relieved does not depend on the InGaAs-layer thickness, the initial strain state, or the composition of the material, but it does strongly depend on the oxidation temperature. The structure of the strain-relaxed InGaAs layer has been investigated using plan-view transmission electron microscopy. It is shown that the misfit dislocation density in In0.3Ga0.7As grown to 15 times the critical thickness (660 Å) has been reduced by two orders of magnitude after lateral oxidation. It is proposed that this is due to interfacial oxidation, which consumes the misfit dislocation cores. © 2000 American Institute of Physics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.65.Mq Oxidation
68.60.Bs Mechanical and acoustical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors

Intersubband electroluminescence using X−Γ carrier injection in a GaAs/AlAs superlattice

C. Domoto, N. Ohtani, K. Kuroyanagi, P. O. Vaccaro, H. Takeuchi, M. Nakayama, and T. Nishimura

Appl. Phys. Lett. 77, 848 (2000); http://dx.doi.org/10.1063/1.1306911 (3 pages) | Cited 1 time

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We report midinfrared electroluminescence originated from an intersubband transition in a GaAs/AlAs superlattice consisting of asymmetric double quantum wells. It is confirmed from interband photoluminescence properties under applied bias voltages that electrons populate at the second Γ (Γ2) subband in the GaAs layer. The electron population results from the carrier injection into the Γ2 subband from the adjacent X1 subband in the AlAs layer, which is initiated by the X1–Γ2 resonance. The energy of the intersubband electroluminescence, 190 meV, agrees with the energy spacing between the Γ2 and Γ1 subbands. This demonstrates that the carrier injection into the higher Γ subband using X–Γ scattering is useful for the design of intersubband-emission devices. © 2000 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Nanoindentation and x-ray diffraction studies of pressure-induced amorphization in C-70 fullerene

Jeremy R. Patterson, Shane A. Catledge, and Yogesh K. Vohra

Appl. Phys. Lett. 77, 851 (2000); http://dx.doi.org/10.1063/1.1306913 (3 pages) | Cited 12 times

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We have carried out high-pressure studies on a C-70 fullerene sample in a diamond anvil cell to 46 GPa at room temperature. Synchrotron energy dispersive x-ray diffraction studies were carried out to monitor the irreversible amorphization transformation followed by nanoindentation studies of the pressure-quenched samples. Micro-Raman studies indicate broad bands at 1570 and 1422 cm−1 indicative of an amorphous phase with a mixture of sp2- and sp3-bonded carbon. Nanoindentation studies on the quenched amorphous phase shows an elastic loading behavior with a hardness of 18 GPa, which is 2–3 times that of the surrounding steel gasket. Our results conclusively establish that the hard carbon phases can be produced from C-70 fullerene by application of pressure at room temperature. © 2000 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
61.43.Er Other amorphous solids
62.50.-p High-pressure effects in solids and liquids
62.20.Qp Friction, tribology, and hardness
64.70.K- Solid-solid transitions
68.35.Gy Mechanical properties; surface strains
78.30.Na Fullerenes and related materials
81.05.ub Fullerenes and related materials

Strong and stable ultraviolet luminescence in porous silicon in situ passivated by manganese

Qianwang Chen, D. L. Zhu, and Y. H. Zhang

Appl. Phys. Lett. 77, 854 (2000); http://dx.doi.org/10.1063/1.1306396 (3 pages) | Cited 9 times

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A strong and stable ultraviolet photoluminescence (PL) band (370 nm) together with a red luminescence band around 670 nm with a 730 nm shoulder were observed in Mn-passivated porous silicon (PS) prepared by the hydrothermal technique. The surface structure is examined by Fourier infrared and x-ray photoelectron spectroscopy analysis. The 670 nm band was confirmed to be the usually observed PL band in PS, and the appearance of the 370 nm band and 730 nm shoulder peak was interpreted based on surface structure characterization and spectroscopy measurements. © 2000 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.55.Mb Porous materials
78.30.Am Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors
81.65.Rv Passivation
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Nonequilibrium electron distributions in a three-subband InGaAs/InAlAs quantum well studied via double resonance spectroscopy

G. B. Serapiglia, K. L. Vodopyanov, and C. C. Phillips

Appl. Phys. Lett. 77, 857 (2000); http://dx.doi.org/10.1063/1.1306651 (3 pages) | Cited 5 times

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Midinfrared optical pumping of electrons from the ground (n = 1) to the first excited (n = 2) subband of the quantum well produces a strongly nonthermal electron distribution which is probed spectroscopically. Two sharp induced absorption peaks appear, associated with electrons which have scattered from the upper subband via longitudinal optical (LO) phonon emission and absorption. The presence of the phonon absorption channel evidences the importance of nonequilibrium LO phonon populations (nph ∼ 1), and the impact on the nonradiative intersubband scattering rates in quantum cascade laser devices is explored. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
71.38.-k Polarons and electron-phonon interactions
72.40.+w Photoconduction and photovoltaic effects
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Thermoelectric figure-of-merit barrier at minimum lattice thermal conductivity?

Gao Min and D. M. Rowe

Appl. Phys. Lett. 77, 860 (2000); http://dx.doi.org/10.1063/1.1306652 (3 pages) | Cited 12 times

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An analysis of the transport properties data on established thermoelectric materials indicates that the ratio of the electrical power factor to optimum electrical conductivity appears constant. This result, when combined with the previously proposed concept of a minimum thermal conductivity, enables realistic maximum dimensionless figures-of-merit to be calculated. It is concluded that a barrier to increasing the dimensionless figure-of-merit appears to exist which is around 2 at room temperature and that overcoming this barrier will require the development of materials with radically different transport properties from those currently available. © 2000 American Institute of Physics.
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72.20.Pa Thermoelectric and thermomagnetic effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
72.10.-d Theory of electronic transport; scattering mechanisms

SiO2-passivated lateral-geometry GaN transparent Schottky-barrier detectors

V. Adivarahan, G. Simin, J. W. Yang, A. Lunev, M. Asif Khan, N. Pala, M. Shur, and R. Gaska

Appl. Phys. Lett. 77, 863 (2000); http://dx.doi.org/10.1063/1.1306647 (3 pages) | Cited 49 times

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We report on a transparent Schottky-barrier ultraviolet detector on GaN layers over sapphire substrates. Using SiO2 surface passivation, reverse leakage currents were reduced to a value as low as 1 pA at 5 V reverse bias for 200 μm diameter device. The device exhibits a high internal gain, about 50, at low forward biases. The response time (about 15 ns) is RC limited, even in the internal gain regime. A record low level of the noise spectral density, 5×10−23 A2/Hz, was measured at 10 Hz. We attribute this low noise level to the reduced reverse leakage current. © 2000 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.65.Rv Passivation
85.60.Dw Photodiodes; phototransistors; photoresistors
73.30.+y Surface double layers, Schottky barriers, and work functions

Effect of oxidation method and post-oxidation annealing on interface properties of metal–oxide–semiconductor structures formed on n-type 4H-SiC C(000math) face

K. Fukuda, W. J. Cho, K. Arai, S. Suzuki, J. Senzaki, and T. Tanaka

Appl. Phys. Lett. 77, 866 (2000); http://dx.doi.org/10.1063/1.1306649 (3 pages) | Cited 16 times

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The C(000math) face of silicon carbide (SiC) has superior properties such as a faster oxidation ratio and a smoother surface compared with the Si(0001) face. We have investigated the oxidation and post-oxidation annealing effects on the capacitance–voltage and the interface state density (Dit) of n-type SiC metal–oxide–semiconductor (MOS) structures formed on the C(000math) face. It was found that pyrogenic oxidation and hydrogen annealing above 700 °C reduced Dit near the conduction-band edge. The value of Dit at Ec−E = 0.2 eV is 1×1012 eV−1 cm−2, which is comparable with that of the MOS structure formed on the Si(0001) face. However, the value of Dit around the deep level at Ec−E = 0.6 eV is one order of magnitude higher than that of n-type MOS structures formed on the Si(0001) face. It is very important to reduce Dit at the deep level for a high-quality SiO2/SiC interface on the 4H-SiC C(000math) face. © 2000 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing
81.05.Hd Other semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Metamorphic InP/InGaAs double-heterojunction bipolar transistors on GaAs grown by molecular-beam epitaxy

H. Q. Zheng, K. Radhakrishnan, H. Wang, K. H. Yuan, S. F. Yoon, and G. I. Ng

Appl. Phys. Lett. 77, 869 (2000); http://dx.doi.org/10.1063/1.1306657 (3 pages) | Cited 16 times

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InP/InGaAs double-heterojunction bipolar transistor (HBT) structures were grown metamorphically on GaAs substrates by solid-source molecular-beam epitaxy. A linearly graded InxGa1−xP (x varying from 0.48 to 1) buffer layer was used to accommodate the strain relaxation. The crystallinity of the buffer layer and the HBT structure was examined by x-ray diffractometry. Devices with 5×5 μm2 emitter area showed a typical peak current gain of 40, a common-emitter breakdown voltage (BVCEO) higher than 9 V, a current gain cut-off frequency (fT) of 46 GHz, and a maximum oscillation frequency (fmax) of 40 GHz. © 2000 American Institute of Physics.
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85.30.Pq Bipolar transistors
84.40.-x Radiowave and microwave (including millimeter wave) technology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties

Room-temperature InAs0.89Sb0.11 photodetectors for CO detection at 4.6 μm

H. H. Gao, A. Krier, and V. V. Sherstnev

Appl. Phys. Lett. 77, 872 (2000); http://dx.doi.org/10.1063/1.1306656 (3 pages) | Cited 20 times

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An InAs0.89Sb0.11 photovoltaic detector that operates at room temperature in the 2.5–5 μm mid-infrared wavelength region is reported. The photodiode has an extended spectral response compared with other currently available III–V room-temperature detectors. In order to accommodate the large lattice mismatch between the InAs0.89Sb0.11 active region and the InAs substrate, a buffer layer with an intermediate composition was introduced into the structure. In this way, we obtained room-temperature photodiodes with a cutoff wavelength near 5 μm, a peak responsivity of 0.8 A/W, and a detectivity of 1.26×109 cm Hz1/2/W. These devices could be effectively used as the basis of an optical sensor for the environmental monitoring of carbon monoxide at 4.6 μm, or as a replacement for PbSe photoconductors. © 2000 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Electron beam-induced increase of electron diffusion length in p-type GaN and AlGaN/GaN superlattices

Leonid Chernyak, Andrei Osinsky, Vladimir Fuflyigin, and E. F. Schubert

Appl. Phys. Lett. 77, 875 (2000); http://dx.doi.org/10.1063/1.1306910 (3 pages) | Cited 24 times

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The diffusion length, L, of electrons in Mg-doped p-GaN grown by metal-organic chemical vapor deposition was found to increase linearly from 0.55 to 2.0 μm during 1500 s of electron beam irradiation. Similar trends were observed for p-type Mg-doped GaN and AlGaN/GaN superlattices grown by molecular-beam epitaxy. While the electron diffusion length in p-(Al)GaN depends on irradiation time, the diffusion length of holes in n-GaN remains unchanged, with L ∼ 0.35 μm. We attribute the observed diffusion length change in p-(Al)GaN to an increase in the minority carrier lifetime. This increase is likely due to electron beam-induced charging of the deep metastable centers associated with Mg doping. The concentration of these centers was estimated to be ∼ 1018 cm−3. The minority carrier diffusion length increase in p-(Al)GaN, which occurs during electron injection, may lead to self-improvement of the bipolar transistor characteristics. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.82.Fk Semiconductors
71.55.Eq III-V semiconductors
81.05.Ea III-V semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species
61.80.Fe Electron and positron radiation effects

Sulfur: A potential donor in diamond

D. Saada, Joan Adler, and R. Kalish

Appl. Phys. Lett. 77, 878 (2000); http://dx.doi.org/10.1063/1.1306914 (2 pages) | Cited 48 times

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We performed first-principle calculations of substitutional sulfur in diamond, in the neutral (S0) and charged states. The energy levels induced by sulfur in diamond are calculated to be 0.15 and 0.5 eV from the bottom of the conduction band, for S0 and the singly ionized state S+, respectively. The formation energy for the neutral state of sulfur is found to be 7.2 eV, lower than that of phosphorus in diamond. The most likely state of sulfur in diamond is found to be the doubly ionized state S++, which cannot act as a donor. However, a small fraction of sulfur can be found in the singly ionized state S+, which can donate an electron for conduction at reasonable temperatures. © 2000 American Institute of Physics.
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71.55.Cn Elemental semiconductors
71.20.Mq Elemental semiconductors
81.05.ub Fullerenes and related materials
81.05.Cy Elemental semiconductors

Pyramidal defects in metalorganic vapor phase epitaxial Mg doped GaN

P. Vennéguès, M. Benaissa, B. Beaumont, E. Feltin, P. De Mierry, S. Dalmasso, M. Leroux, and P. Gibart

Appl. Phys. Lett. 77, 880 (2000); http://dx.doi.org/10.1063/1.1306421 (3 pages) | Cited 53 times

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A transmission electron microscopy study of structural defects induced by the introduction of Mg during the growth of metalorganic vapor phase epitaxy GaN is presented. These defects are assumed to be pyramidal inversion domains with an hexagonal base and {11math3} inclined facets. The tip of the pyramids is always pointing toward the [000math] direction, i.e., in a Ga-terminated film, toward the substrate and in a N-terminated film, toward the surface. A chemical quantitative analysis shows that these pyramidal defects are Mg rich. They are present in all the studied films, independent of the doping level. © 2000 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.-y Defects and impurities in crystals; microstructure
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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Temporal evolution of spin-polarization in ferromagnetic tunnel junctions

D. J. Monsma and S. S. P. Parkin

Appl. Phys. Lett. 77, 883 (2000); http://dx.doi.org/10.1063/1.1306641 (3 pages) | Cited 16 times

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The spin polarization of the simple transition-metal ferromagnets Fe, Co, and Ni can be measured using ferromagnet/insulator/superconductor tunneling structures. Measurements, carried out over the past 20 years using superconducting aluminum electrodes and alumina tunneling barriers, have given a wide range of values, especially for Ni. In this letter, we show that high-spin-polarization values are found for Ni using superconducting films formed from Cu-doped aluminum deposited in a high-vacuum sputter-deposition system. However, we find that the magnitude of the spin polarization slowly decreases over time, which we believe to result from a reaction between Ni and alumina. We conclude that the spin-polarization values measured in such studies are strongly influenced by the detailed structure of the ferromagnet–superconductor interface. © 2000 American Institute of Physics.
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75.50.Cc Other ferromagnetic metals and alloys
68.35.Ct Interface structure and roughness
74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

6% magnetic-field-induced strain by twin-boundary motion in ferromagnetic Ni–Mn–Ga

S. J. Murray, M. Marioni, S. M. Allen, R. C. O’Handley, and T. A. Lograsso

Appl. Phys. Lett. 77, 886 (2000); http://dx.doi.org/10.1063/1.1306635 (3 pages) | Cited 395 times

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Field-induced strains of 6% are reported in ferromagnetic Ni–Mn–Ga martensites at room temperature. The strains are the result of twin boundary motion driven largely by the Zeeman energy difference across the twin boundary. The strain measured parallel to the applied magnetic field is negative in the sample/field geometry used here. The strain saturates in fields of order 400 kA/m and is blocked by a compressive stress of order 2 MPa applied orthogonal to the magnetic field. The strain versus field curves exhibit appreciable hysteresis associated with the motion of the twin boundaries. A simple model accounts quantitatively for the dependence of strain on magnetic field and external stress using as input parameters only measured quantities. © 2000 American Institute of Physics.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Cc Other ferromagnetic metals and alloys
61.72.Mm Grain and twin boundaries
81.40.Jj Elasticity and anelasticity, stress-strain relations

Reduced coercivity in ferromagnetic Co–Cu coevaporated epitaxial films on Cu(111)

J. E. Prieto, J. Camarero, J. J. de Miguel, R. Miranda, Ch. Rath, S. Müller, L. Hammer, and K. Heinz

Appl. Phys. Lett. 77, 889 (2000); http://dx.doi.org/10.1063/1.1306650 (3 pages) | Cited 3 times

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Epitaxial films grown by coevaporation of Co and Cu on Cu(111) were investigated by low-energy electron diffraction and surface magneto-optical Kerr-effect measurements. The films are dominantly face-centered-cubic stacked up to high Co concentrations and exhibit ferromagnetism. Their coercivity is significantly reduced compared to pure Co films produced by thermal Co deposition on Cu(111) independent of the use of Pb as a surfactant. © 2000 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Layer selective determination of magnetization vector configurations in an epitaxial double spin valve structure: Si(001)/Cu/Co/Cu/FeNi/Cu/Co/Cu

B. C. Choi, A. Samad, C. A. F. Vaz, J. A. C. Bland, S. Langridge, and J. Penfold

Appl. Phys. Lett. 77, 892 (2000); http://dx.doi.org/10.1063/1.1306395 (3 pages) | Cited 3 times

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The magnetization vector configurations in an epitaxial Si(001)/Cu/Co/Cu/Fe20Ni80/Cu/Co/Cu double spin valve structure have been investigated at room temperature using polarized neutron reflectivity measurements. The layer-averaged magnetic moment per FeNi atom was found to be 0.99±0.06 μB at saturation, while the top (bottom) Co layer moment was 1.69±0.09 μB (1.67±0.08 μB), which are identical to the bulk values within experimental error. Furthermore, the Co magnetization vectors are found to lie in-plane but canted with respect to the applied field direction for an applied field strength smaller than the coercive fields (∼80 and 130 Oe) of the Co layers. This result indicates that a complete antiparallel alignment of the layer magnetizations is not reached causing a corresponding reduction in the giant magnetoresistance (GMR). These observations emphasize the importance of the detailed spin configuration in determining the GMR amplitude at low fields. © 2000 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities

SmNi4B: A narrow domain-wall ferromagnet

Chandan Mazumdar, R. Nagarajan, L. C. Gupta, B. D. Padalia, and R. Vijayaraghavan

Appl. Phys. Lett. 77, 895 (2000); http://dx.doi.org/10.1063/1.1306294 (3 pages) | Cited 19 times

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We have investigated magnetic properties of SmNi4B. The material undergoes a ferromagnetic ordering at TC ≈ 39 K, which, surprisingly, is higher than that of isostructural GdNi4B ( ≈ 36 K). The saturation magnetic moment is rather small (0.15 μB per Sm at 5 K), suggesting the presence of crystal-field effects. Below TC, the material exhibits a large thermomagnetic irreversibility and also a large magnetic hysteresis at 5 K with a coercive field ≈ 28 kOe, which is one of the largest observed in a Sm-based material. We suggest that the large coercive field is intrinsic, associated with narrow domain walls of thickness of only one atomic layer, which resembles a ferroelectric wall. © 2000 American Institute of Physics.
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75.60.Ch Domain walls and domain structure
75.50.Cc Other ferromagnetic metals and alloys
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
71.70.Ch Crystal and ligand fields
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Investigation of interface and bulk fatigue scenarios in sol-gel derived Pb(Zr0.5Ti0.5)O3 films by asymmetric field driving

Biao Li, F. Koch, X. J. Meng, J. G. Cheng, and J. H. Chu

Appl. Phys. Lett. 77, 898 (2000); http://dx.doi.org/10.1063/1.1306609 (3 pages) | Cited 6 times

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A method to distinguish the bulk and interface scenarios of fatigue in sol-gel derived Pb(Zr0.5Ti0.5)O3 (PZT) thin films on Pt and LaNiO3 (LNO) substrates is proposed based on the asymmetric electric field driving of capacitors. The “hard” and “soft” failures of polarization, which are typical for sputtering and sol-gel deposited PZT, respectively, are realized in sol-gel derived Pt/PZT/Pt capacitors by changing the asymmetricity of driving pulses, indicating that the interface plays an important role in the polarization breakdown. For Pt/PZT/LNO capacitors, it is shown that the bulk pinning of domains appears to be more evident than the interface pinning. A model based on the electromigration and entrapment of charged defects subjected to the asymmetric field is also given, and the plausible approximation of space charge field versus charge density is discussed. © 2000 American Institute of Physics.
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77.55.-g Dielectric thin films
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)
77.22.Jp Dielectric breakdown and space-charge effects
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
66.30.Qa Electromigration
71.55.Ht Other nonmetals
73.20.Hb Impurity and defect levels; energy states of adsorbed species
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Porous-silicon vapor sensor based on laser interferometry

Jun Gao, Ting Gao, and Michael J. Sailor

Appl. Phys. Lett. 77, 901 (2000); http://dx.doi.org/10.1063/1.1306640 (3 pages) | Cited 44 times

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Certain porous-silicon (PS) films exhibit well-resolved Fabry–Pérot fringes in their optical reflection spectra due to thin-film interference. The fringes shift to higher wavelengths when the PS is exposed to vapors from organic solvents, as a result of an increase in the average refractive index of the PS layer. If a small diode laser is used as the light source, the shift of the Fabry–Pérot fringes upon analyte adsorption results in a change in the reflected light intensity, which correlates with the concentration of the analyte (ethanol) in an air stream. Based on this principle, a PS vapor sensor has been demonstrated with a detection limit of 500 ppb and a dynamic range of nearly five orders of magnitude. © 2000 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
81.05.Cy Elemental semiconductors
81.05.Rm Porous materials; granular materials
78.66.Db Elemental semiconductors and insulators
61.43.Gt Powders, porous materials
68.55.-a Thin film structure and morphology
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.25.Hz Interference
07.60.Ly Interferometers

High-efficiency organic electrophosphorescent devices with tris(2-phenylpyridine)iridium doped into electron-transporting materials

Chihaya Adachi, Marc A. Baldo, Stephen R. Forrest, and Mark E. Thompson

Appl. Phys. Lett. 77, 904 (2000); http://dx.doi.org/10.1063/1.1306639 (3 pages) | Cited 419 times

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We demonstrate high-efficiency organic light-emitting devices employing the green electrophosphorescent molecule, fac tris(2-phenylpyridine)iridium [Ir(ppy)3], doped into various electron-transport layer (ETL) hosts. Using 3-phenyl-4-(1′-naphthyl)-5-phenyl-1,2,4-triazole as the host, a maximum external quantum efficiency (ηext) of 15.4±0.2% and a luminous power efficiency of 40±2 Im/W are achieved. We show that very high internal quantum efficiencies (approaching 100%) are achieved for organic phosphors with low photoluminescence efficiencies due to fundamental differences in the relationship between electroluminescence from triplet and singlet excitons. Based on the performance characteristics of single and double heterostructures, we conclude that exciton formation in Ir(ppy)3 occurs within close proximity to the hole-transportlayer/ETL:Ir(ppy)3 interface. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
78.55.Kz Solid organic materials
78.60.Fi Electroluminescence
71.35.-y Excitons and related phenomena

Amorphous silicon air-gap resonators on large-area substrates

M. Boucinha, P. Brogueira, V. Chu, and J. P. Conde

Appl. Phys. Lett. 77, 907 (2000); http://dx.doi.org/10.1063/1.1306912 (3 pages) | Cited 16 times

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Air-gap resonators composed of bridges of hydrogenated amorphous silicon and aluminum bilayers on glass and polyethylene terephthalate substrates are realized using surface micromachining techniques. The resonance frequency of structures on plastic substrates was found to vary inversely with the square of the length of the bridge span. On glass substrates, this dependence is seen for lengths >100 μm, while for lengths <100 μm, a decrease in the frequency is attributed to compressive stress. Resonance frequencies of ∼ 500 kHz to ∼ 2 MHz were measured in bridges with lengths from 160 μm down to ∼ 80 μm. © 2000 American Institute of Physics.
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07.10.Cm Micromechanical devices and systems
81.20.Wk Machining, milling
81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors
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Focused nanoparticle-beam deposition of patterned microstructures

F. Di Fonzo, A. Gidwani, M. H. Fan, D. Neumann, D. I. Iordanoglou, J. V. R. Heberlein, P. H. McMurry, S. L. Girshick, N. Tymiak, W. W. Gerberich, and N. P. Rao

Appl. Phys. Lett. 77, 910 (2000); http://dx.doi.org/10.1063/1.1306638 (3 pages) | Cited 44 times

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A method was developed for fabricating nanocrystalline microstructures. This method involves synthesizing nanoparticles in a thermal plasma expanded through a nozzle, and then focusing the nanoparticles to a collimated beam by means of aerodynamic lenses. High-aspect-ratio structures of silicon carbide and titanium were deposited on stationary substrates, and lines and two-dimensional patterns were deposited on translated substrates. Linewidths equalled approximately 50 μm. This approach allows the use of much larger nozzles than in previously developed micronozzle methods, and also allows size selection of the particles that are deposited. © 2000 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
61.46.-w Structure of nanoscale materials
07.10.Cm Micromechanical devices and systems

Imaging of charge transport in polycrystalline diamond using ion-beam-induced charge microscopy

P. J. Sellin, M. B. H. Breese, A. P. Knights, L. C. Alves, R. S. Sussmann, and A. J. Whitehead

Appl. Phys. Lett. 77, 913 (2000); http://dx.doi.org/10.1063/1.1306259 (3 pages) | Cited 12 times

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Studies have been made using a 1 μm spatial resolution ion-beam-induced charge (IBIC) technique of the charge transport distribution in polycrystalline diamond produced by chemical vapor deposition. The devices tested used a coplanar electrode structure fabricated only on the growth side of the diamond film, and were predominantly sensitive to charge transport close to the growth surface of the diamond film where the diamond crystallites are largest. Irradiation with 5.48 MeV alpha particles gave a pulse height spectrum with a broad full energy peak and a mean charge collection efficiency of 15%. IBIC images obtained using microfocus proton and alpha particle beams showed spatially resolved regions of high charge collection efficiency correlating to individual diamond crystallites with a typical width of 20 μm, as observed by secondary electron microscopy. © 2000 American Institute of Physics.
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73.61.Cw Elemental semiconductors
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
29.40.Wk Solid-state detectors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
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