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27 Mar 2000

Volume 76, Issue 13, pp. 1641-1784

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A study of Ar+ laser-assisted Si doping of GaAs by chemical beam epitaxy

B. Q. Shi and C. W. Tu

Appl. Phys. Lett. 76, 1716 (2000); http://dx.doi.org/10.1063/1.126145 (3 pages)

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Doping results from Ar+ laser-assisted chemical beam epitaxy with triethylgallium, tris(dimethylamino) arsenic, and silicon tetrabromide precursors are reported. Enhancements in the n-type doping concentration are observed with laser irradiation in the substrate–temperature range 390–500 °C. With a 300 W/cm2 irradiation power density, a 70-fold increase in the carrier concentration is obtained at 390 °C substrate temperature. An expression for doping concentration is derived to assess the contribution of laser-induced thermal heating to the observed doping increase. Effects of photogenerated carriers on surface decomposition of metalorganic species are discussed. We postulate that the dramatic increase in carrier concentration at low growth temperatures is due to photolysis of silicon tetrabromide. © 2000 American Institute of Physics.
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81.05.Ea III-V semiconductors
61.72.uj III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.S- Impurities in crystals

Experimental evidence for recombination-assisted leakage in thin oxides

Daniele Ielmini, Alessandro S. Spinelli, and Andrea L. Lacaita

Appl. Phys. Lett. 76, 1719 (2000); http://dx.doi.org/10.1063/1.126146 (3 pages) | Cited 6 times

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Carrier separation experiments in degraded p-channel metal–oxide–semiconductor devices reveal the occurrence of both electron and hole leakage processes. A detailed study of the excess currents as a function of time after stress, stress fluence, and polysilicon doping is presented. Evidence for a linear correlation between electron and hole leakage currents is provided, suggesting that the same defect species are responsible for both leakage phenomena. The dependence on polysilicon gate type confirms this explanation, supporting a leakage model based on trap-assisted tunneling and recombination in oxide traps. © 2000 American Institute of Physics.
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73.61.Ng Insulators
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.25.+i Surface conductivity and carrier phenomena
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Hole-induced transient bandgap renormalization: A mechanism for photo-induced absorption in defect-engineered semiconductors

Paul W. Juodawlkis and Stephen E. Ralph

Appl. Phys. Lett. 76, 1722 (2000); http://dx.doi.org/10.1063/1.126147 (3 pages) | Cited 5 times

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In semiconductors, photoexcitation often results in a transient band edge-absorption bleaching due to the dominance of conduction-band filling over bandgap renormalization. In this letter, we show that the presence of electron traps can act to reverse this behavior so that photoexcitation results in an absorption increase in these same semiconductors. We associate this photo-induced absorption with bandgap renormalization caused by photoexcited holes that remain after the electrons have become trapped. We develop a dynamic model that predicts the wavelength dependence of photo-induced absorption and accurately describes the measured nonlinear-absorption recovery of low-temperature-grown InGaAs/InAlAs multiple quantum wells. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Modification of GaN Schottky barrier interfaces probed by ballistic-electron-emission microscopy and spectroscopy

L. D. Bell, R. P. Smith, B. T. McDermott, E. R. Gertner, R. Pittman, R. L. Pierson, and G. J. Sullivan

Appl. Phys. Lett. 76, 1725 (2000); http://dx.doi.org/10.1063/1.126148 (3 pages) | Cited 6 times

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Ballistic-electron-emission microscopy (BEEM) and spectroscopy have been used to investigate the properties of Au/GaN interfaces. The effects of in situ and ex situ annealing on the starting GaN surface were examined, with the aim of increasing the surprisingly low value of interface electron transmission observed in previous BEEM measurements. BEEM imaging and spectroscopy have demonstrated that much higher, more uniform transmission across the Au/GaN interface can be achieved. However, while methods were identified that increase transmission by more than an order of magnitude, BEEM spectroscopy indicates that annealing can substantially alter the Schottky barrier height. These barrier height changes at moderate temperatures are attributed to vacancy diffusion. © 2000 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
81.05.Ea III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
68.37.Vj Field emission and field-ion microscopy

Effects of alloy disorder on the transport properties of AlxGa1−xN epilayers probed by persistent photoconductivity

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

Appl. Phys. Lett. 76, 1728 (2000); http://dx.doi.org/10.1063/1.126149 (3 pages) | Cited 10 times

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The effects of alloy fluctuations on the transport properties of AlxGa1−xN alloys (x ∼ 0.35) have been probed through the use of persistent photoconductivity (PPC). In the PPC state, the electron mobility, μe, as a function of electron concentration, n, in a single sample can be obtained under controlled light illumination conditions. It was found that μe is a constant when n is below a critical value nc and it then increases with n at n>nc. This mobility behavior was attributed to the effects of alloy fluctuations in AlxGa1−xN alloys. As a result, the initial PPC buildup kinetics seen in AlxGa1−xN alloys was quite different from those in better understood semiconductor alloys, such as AlGaAs and ZnCdSe, and is a direct consequence of the observed unique dependence of μe on n. From these measurements, the total density of the tail states below the mobility edge in the conduction band was estimated to be 1.46×1017 cm−3 in a Al0.35Ga0.65N sample. The results were compared with those in II–VI semiconductor alloys and their implications on III-nitride device applications were discussed. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
72.40.+w Photoconduction and photovoltaic effects
73.50.Dn Low-field transport and mobility; piezoresistance

Addition energies and quasiparticle gap of CdSe nanocrystals

Alberto Franceschetti and Alex Zunger

Appl. Phys. Lett. 76, 1731 (2000); http://dx.doi.org/10.1063/1.126150 (3 pages) | Cited 19 times

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Using atomistic pseudopotential wave functions we calculate the quasiparticle gap, the optical gap and the electron and hole addition energies of CdSe nanocrystals. We find that the quasiparticle gap and the addition energies depend strongly on the dielectric constant of the surrounding material, while the optical gap is rather insensitive to the environment. We provide scaling lows for these quantities as a function of the quantum dot size, and compare our results with recent scanning tunneling spectroscopy experiments. © 2000 American Institute of Physics.
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73.22.-f Electronic structure of nanoscale materials and related systems
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Dz II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
61.46.-w Structure of nanoscale materials
71.20.Nr Semiconductor compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
78.66.Hf II-VI semiconductors

Transient and steady-state space-charge-limited currents in polyfluorene copolymer diode structures with ohmic hole injecting contacts

Alasdair J. Campbell, Donal D. C. Bradley, Homer Antoniadis, Mike Inbasekaran, Weishi W. Wu, and Ed P. Woo

Appl. Phys. Lett. 76, 1734 (2000); http://dx.doi.org/10.1063/1.126182 (3 pages) | Cited 47 times

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We report detailed measurements on diode structures containing the electroluminescent polyfluorene copolymer poly(9,9-dioctylfluorene-co-bis-N,N′-(4-methoxyphenyl)-bis-N,N′-phenyl-1,4 phenylenediamine). Ohmic injection of holes is achieved with an oxygen plasma cleaned indium tin oxide (ITO) electrode, untreated ITO coated with a film of poly(ethylenedioxythiophene)/polystyrenesulphonic acid (PEDOT/PSS) and plasma cleaned ITO with PEDOT/PSS. Transient dark injection and time-of-flight mobility measurements and steady state current density versus voltage measurements are then entirely consistent with a positive carrier, trap-free, space-charge-limited current. Injection limited behavior is observed, however, for untreated ITO without PEDOT/PSS and for evaporated Au contacts. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics
72.20.Ht High-field and nonlinear effects
73.50.Fq High-field and nonlinear effects
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning
72.80.Le Polymers; organic compounds (including organic semiconductors)

Effect of silicon doping on the optical and transport properties of InGaN/GaN multiple-quantum-well structures

T. Wang, H. Saeki, J. Bai, T. Shirahama, M. Lachab, S. Sakai, and P. Eliseev

Appl. Phys. Lett. 76, 1737 (2000); http://dx.doi.org/10.1063/1.126151 (3 pages) | Cited 28 times

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Temperature-dependent photoluminescence and transport measurements were performed on the In0.13Ga0.87N:Si/GaN:Si multiple-quantum-well (MQW) structures with different doping levels. By fitting the temperature-dependent emission energy of these samples using the band tail model, an obvious localization effect is observed in lightly doped MQW structures. Correspondingly, the electron mobilities in these structures are significantly higher than those of undoped and heavily doped MQW structures. Furthermore, when the localization effect is stronger, the mobility is higher. © 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
73.21.-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
73.50.Dn Low-field transport and mobility; piezoresistance
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Surface polarity dependence of Mg doping in GaN grown by molecular-beam epitaxy

L. K. Li, M. J. Jurkovic, W. I. Wang, J. M. Van Hove, and P. P. Chow

Appl. Phys. Lett. 76, 1740 (2000); http://dx.doi.org/10.1063/1.126152 (3 pages) | Cited 51 times

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The effect of surface polarity on the growth of Mg-doped GaN thin films on c-plane sapphire substrates by molecular-beam epitaxy has been investigated. The doping behavior of Mg and resulting conductivity of the doped layers were found to strongly depend on the surface polarity of the growing GaN planes. The samples grown on the Ga-polar face (A face) exhibited a p-type conductivity with a free-hole concentration up to 5×1017 cm−3, while the samples grown on the N-polar face (B face) were highly resistive or semi-insulating. The incorporation of residual impurities (O, Si, and C) in the two different polar surfaces was studied by secondary ion mass spectrometry analysis and its effect on the Mg doping was discussed. Our results suggest that the A face (Ga face) is the favored surface polarity for achieving p-type conductivity during the growth of Mg-doped GaN. © 2000 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Ey III-V semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
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Crystallographic and magneto-optical studies of nanoscaled MnSb dots grown on GaAs

M. Mizuguchi, H. Akinaga, K. Ono, and M. Oshima

Appl. Phys. Lett. 76, 1743 (2000); http://dx.doi.org/10.1063/1.126153 (3 pages) | Cited 14 times

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MnSb ultrathin films with the nominal thickness of 0–1.40 nm were grown on sulfur passivated GaAs substrates by molecular beam epitaxy. Atomic force microscopy analysis showed that MnSb formed nanosize clusters on the substrate, and the coalescence of the clusters occurred at the nominal thickness between 0.70 and 1.05 nm. The intensity of the polar magnetic circular dichroism of MnSb clusters suddenly increased when the nominal thickness reached the critical value of 1.05 nm. The coalescence among the dots can be correlated with the sharp increase of the magnetic circular dichroism intensity. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Li Other semiconductors
75.50.Pp Magnetic semiconductors
78.20.Ls Magneto-optical effects
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Hd Other semiconductors

Nanocomposite Nd-rich Nd–Fe–B alloys: Approaching ideal Stoner–Wohlfarth type behavior

Er. Girt, Kannan M. Krishnan, G. Thomas, and Z. Altounian

Appl. Phys. Lett. 76, 1746 (2000); http://dx.doi.org/10.1063/1.126154 (3 pages) | Cited 20 times

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Starting from rapidly quenched NdδFe13.1B(2.05 ⩽ δ ⩽ 147.6) alloys and by appropriate annealing, the microstructure was tailored from strongly interacting Nd2Fe14B grains to magnetically isolated single domain Nd2Fe14B grains embedded in a nonmagnetic Nd-rich matrix (α-Nd and γ-Nd). This change in microstructure was found to have a large effect on coercivity, i.e., coercivity, μ0Hc, increases with an increase of the Nd concentration from 1.25 T in Nd2.05Fe13.1B to 2.75 T in Nd147.6Fe13.1B at 290 K. Using transmission electron microscopy, the Nd2Fe14B grains in Nd147.6Fe13.1B were confirmed to be randomly oriented platelets with the c axis normal to the plate and an average size of 100×40×25 nm. For these randomly oriented, noninteracting, single domain Nd2Fe14B grains, the coercivity was calculated using a Stoner–Wohlfarth model which included the shape anisotropy of the grains. The observed coercivity of Nd2Fe14B in such nanocomposite Nd147.6Fe13.1B alloys is ∼83% of its theoretical value. © 2000 American Institute of Physics.
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75.50.Ww Permanent magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.50.Tt Fine-particle systems; nanocrystalline materials
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
75.50.Bb Fe and its alloys

Phonon spectrometry with a bolometer based on spin-lattice relaxation

A. M. Witowski, H.-P. Moll, M. L. Sadowski, P. Wyder, G. Karczewski, J. Kossut, and T. Wojtowicz

Appl. Phys. Lett. 76, 1749 (2000); http://dx.doi.org/10.1063/1.126155 (3 pages)

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We discuss the possibility of a bolometer based on the effect of spin-lattice relaxation detected by a pickup coil. The system is composed of an epitaxial layer of CdMnTe on a GaAs substrate, grown by molecular beam epitaxy (MBE). The “phonon wave,” generated by a light pulse on the back surface of the substrate, changes the spin alignment in the MBE layer, thus also changing its magnetization. This change is detected by a pickup coil. The possible use of such a system as a bolometer and “phonon spectrometer” is discussed. © 2000 American Institute of Physics.
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63.20.-e Phonons in crystal lattices
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Linewidth of a resistively shunted high-temperature-superconductor Josephson heterodyne oscillator

J. C. Macfarlane, L. Hao, D. A. Peden, and J. C. Gallop

Appl. Phys. Lett. 76, 1752 (2000); http://dx.doi.org/10.1063/1.126156 (3 pages) | Cited 11 times

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High-temperature-superconducting (HTS) resistively shunted superconducting quantum interference devices, consisting of two yttrium–barium–copper–oxide (YBCO) grain boundary junctions shunted by gold-film resistors of ∼20 μΩ, have been prepared and characterized at temperatures from 17 to 74 K. The small value and stability of the resistor allows narrow-band heterodyne oscillations to be generated between the Josephson oscillations in the individual junctions. The frequency can be precisely controlled in accordance with the ac Josephson effect by adjustment of an external current applied to the YBCO–Au–YBCO shunt resistor, and the linewidth is determined in principle only by Johnson noise in the resistor. Off-chip detection and spectral analysis of the heterodyne signal generated in this way has not been previously reported. Measurements of the signal power (∼nW), the tunability of the center frequency from 5 to 50 MHz, the frequency stability and the linewidth of the heterodyne Josephson oscillation are described. Although linewidth broadening due to nonthermal fluctuations is observed, the linewidth of ∼30 kHz at T = 17 K, at a center frequency of 24 MHz, is believed to be the narrowest reported for Josephson oscillations in an HTS device of this type. © 2000 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.72.-h Cuprate superconductors
74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
74.78.-w Superconducting films and low-dimensional structures
74.40.-n Fluctuation phenomena

Low angle grain boundary transport in YBa2Cu3O7−δ coated conductors

D. T. Verebelyi, D. K. Christen, R. Feenstra, C. Cantoni, A. Goyal, D. F. Lee, M. Paranthaman, P. N. Arendt, R. F. DePaula, J. R. Groves, and C. Prouteau

Appl. Phys. Lett. 76, 1755 (2000); http://dx.doi.org/10.1063/1.126157 (3 pages) | Cited 99 times

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Second generation, high-temperature superconducting wires are based on buffered, metallic tape substrates of near single crystal texture. Strong alignment of adjacent grains was found to be necessary from previous work that suggested large angle, YBa2Cu3O7−δ [001]-tilt boundaries reduce Jc exponentially with increasing misorientation angle (θ). We pursue the low-θ regime by evaluating single grain boundaries (GB) and biaxially aligned polycrystalline films utilizing both the rolling-assisted biaxially textured substrates and ion-beam assisted deposition coated conductor architectures. Analysis concludes that an exponential dependence on Jc is applicable for θ≳4°, where the spacing between the periodic disordered regions along the GB become smaller than a coherence length. © 2000 American Institute of Physics.
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84.71.Mn Superconducting wires, fibers, and tapes
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
61.72.Mm Grain and twin boundaries
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
74.25.Sv Critical currents
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Low-temperature preparation and characterization of SrBi2Ta2O9 thin films on (100)-oriented LaNiO3 electrodes

G. D. Hu, I. H. Wilson, J. B. Xu, C. P. Li, and S. P. Wong

Appl. Phys. Lett. 76, 1758 (2000); http://dx.doi.org/10.1063/1.126158 (3 pages) | Cited 23 times

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SrBi2Ta2O9 (SBT) ferroelectric thin films were prepared by the metalorganic decomposition technique at annealing temperatures of 600 and 650 °C on Pt/Ti/SiO2/Si substrates coated by (100)-oriented LaNiO3 (LNO) metal oxide thin films, which were fabricated by the sol–gel technique combined with a layer-by-layer annealing method at 600 °C. A (200)-predominant SBT thin film can be formed on LaNiO3(100)/Pt/Ti/SiO2/Si substrate at 600 °C. The effect of the LNO oxide electrode on the dielectric and ferroelectric properties of SBT thin film annealed at 600 °C was studied. Although the remanent polarization of the (200)-predominant SBT thin film is not as large as expected, the film can be uniformly polarized and imaged using an atomic force microscope in the piezoelectric mode. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
77.80.Dj Domain structure; hysteresis
68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
77.22.Ej Polarization and depolarization
77.80.Fm Switching phenomena

Na0.5K0.5NbO3/SiO2/Si thin film varactor

Choong-Rae Cho, Jung-Hyuk Koh, Alex Grishin, Saeed Abadei, and Spartak Gevorgian

Appl. Phys. Lett. 76, 1761 (2000); http://dx.doi.org/10.1063/1.126159 (3 pages) | Cited 34 times

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Perfectly c-axis oriented micrometer thick Na0.5K0.5NbO3(NKN) films have been prepared on a thermally grown ultrathin SiO2 template layer onto a Si(001) wafer by the pulsed laser deposition technique. A x-ray diffraction θ–2θ scan reveals multiple-cell structuring of single phase NKN film along the polar axis, while films grown onto amorphous ceramic (Corning) glass show a mixture of slightly c-axis oriented NKN and pyrochlore phases. This implies a small amount of SiO2 crystallites distributed in an amorphous matrix inherit Si(001) orientation and promotes highly oriented NKN film growth. NKN film dielectric permittivity ε′ was found to vary from 114.0 to 107.2 in the frequency range 1 kHz–1 MHz, while the resistivity was on the order of 2.6×1010 Ω cm @ 20 kV/cm. The planar interdigital variable reactance device (varactor) based on the NKN/SiO2/Si thin film structure possesses a dissipation factor of 0.8% at 1 MHz and zero bias, electrical tunability of 3.1%, and nA order leakage current at 20 V bias at room temperature. © 2000 American Institute of Physics.
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84.32.Tt Capacitors
81.15.Fg Pulsed laser ablation deposition
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Noise and conversion properties of Y–Ba–Cu–O Josephson mixers at operating temperatures above 20 K

Oliver Harnack, Marian Darula, Stephan Beuven, and Hermann Kohlstedt

Appl. Phys. Lett. 76, 1764 (2000); http://dx.doi.org/10.1063/1.126160 (3 pages) | Cited 5 times

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We have measured the noise performance and conversion efficiency of Y–Ba–Cu–O bicrystal Josephson mixers at operating temperatures between 20 and 60 K and at operating frequencies around 90 GHz. A double-sideband mixer noise temperature of about 1600 K and a conversion efficiency of −10 dB at 20 K operating temperature has been measured using the Y-factor method. The absorbed local oscillator power was in the range of 10 nW. The dependence of the mixer performance on the normalized frequency Ω and the fluctuation parameter Γ has been studied. In accordance with the resistively shunted junction model, the experimental data show the presence of excess noise. The temperature dependence of the mixer noise temperature can be explained by the variation of the linewidth of the Josephson oscillations with the operating temperature. © 2000 American Institute of Physics.
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85.25.Cp Josephson devices
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
84.40.-x Radiowave and microwave (including millimeter wave) technology
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors

Al composition dependence of breakdown voltage in AlxGa1−xN Schottky rectifiers

A. P. Zhang, G. Dang, F. Ren, J. Han, A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, J. M. Redwing, X. A. Cao, and S. J. Pearton

Appl. Phys. Lett. 76, 1767 (2000); http://dx.doi.org/10.1063/1.126161 (3 pages) | Cited 27 times

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Planar geometry, lateral Schottky rectifiers were fabricated on high resistivity AlxGa1−xN (x = 0–0.25) epitaxial layers grown on sapphire substrates. The reverse breakdown voltages of unpassivated devices increased with Al composition, varying from 2.3 kV for GaN to 4.3 kV for Al0.25Ga0.75N. The reverse current–voltage (I–V) characteristics showed classical Shockley–Read–Hall recombination as the dominant mechanism, with I∝V0.5. The reverse current density in all diodes was in the range 5–10×10−6 A cm−2 at 2 kV. The use of p+ guard rings was effective in preventing premature edge breakdown and with optimum ring width increased VB from 2.3 to 3.1 kV in GaN diodes. © 2000 American Institute of Physics.
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85.30.Kk Junction diodes
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
73.61.Ey III-V semiconductors
73.50.Fq High-field and nonlinear effects

Transient electroluminescence under double voltage pulse: Charge accumulation in light-emitting devices based on alizarin violet

Sharmistha Das and Amlan J. Pal

Appl. Phys. Lett. 76, 1770 (2000); http://dx.doi.org/10.1063/1.126162 (3 pages) | Cited 18 times

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Transient characteristics of organic light-emitting devices with alizarin violet as emitting material have been studied. A sequence of two voltage pulses separated by a time delay was applied. From the transient response of electroluminescence, the effects of accumulated and injected carriers have been separated out. During the first voltage pulse, the intrinsically accumulated charges generated a peak in luminance, which was absent during the latter pulses. The separation time between the two pulses has been varied to study the relaxation dynamics of the accumulated carriers. By varying the molar concentration of the emitting material, we have studied the parameters related to electron barrier modification and discussed the contribution of accumulated carriers in device operation. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
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Electron-beam-induced conduction in a ruthenium carbonyl nanoparticle polymer

M. D. R. Thomas, H. Ahmed, K. M. Sanderson, D. S. Shephard, B. F. G. Johnson, and W. Zhou

Appl. Phys. Lett. 76, 1773 (2000); http://dx.doi.org/10.1063/1.126163 (3 pages) | Cited 3 times

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A polymer composed of ruthenium carbonyl and of the formula [Ru6C(CO)15Ph2PCCPPh2]n has been synthesized. It is found to behave as a negative electron-beam resist with a sensitivity of 400 C/m2. Upon exposure to the electron beam, the electrical conductivity of the patterned films is found to vary over seven orders of magnitude according to a power-law dependence on dose. Temperature dependence of the conductivity is studied, and the conduction is attributed to variable-range hopping between ruthenium superclusters in two dimensions. © 2000 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance
85.40.Hp Lithography, masks and pattern transfer
73.63.-b Electronic transport in nanoscale materials and structures

Field emission from well-aligned, patterned, carbon nanotube emitters

Hirohiko Murakami, Masaaki Hirakawa, Chiaki Tanaka, and Hiroyuki Yamakawa

Appl. Phys. Lett. 76, 1776 (2000); http://dx.doi.org/10.1063/1.126164 (3 pages) | Cited 179 times

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We have developed a process to fabricate well-aligned, patterned, carbon nanotube field emitters on glass substrates. The process consists of depositing and patterning a nickel-based metal line on the glass substrate followed by a bias-enhanced microwave plasma chemical vapor deposition to grow carbon nanotube emitters. A turn-on field of 1.2 V/μm, and emission currents of 1 mA/cm2 at 3 V/μm were achieved on well-aligned carbon nanotube emitters. A test of cathode-ray tube lighting elements now underway suggests a lifetime of exceeding 10 000 h. © 2000 American Institute of Physics.
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73.61.Wp Fullerenes and related materials
79.70.+q Field emission, ionization, evaporation, and desorption
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
71.20.Tx Fullerenes and related materials; intercalation compounds

An optical spin micromotor

Zong-Ping Luo, Yu-Long Sun, and Kai-Nan An

Appl. Phys. Lett. 76, 1779 (2000); http://dx.doi.org/10.1063/1.126165 (3 pages) | Cited 28 times

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An optical spin micromotor operated by optical tweezers, described in the present study, converts radiant energy directly to mechanical energy. This conversion is of great practical and fundamental interest. The optical spin micromotor consists of a two-bead linkage. The large bead (2.0 μm in diameter) is trapped by the optical tweezers and rotates around the laser beam axis. The small bead (0.94 μm in diameter) is partially coated with gold/palladium for generating the spin torque through the change of momentum from gradient radiation pressure of the same laser applied on the coated small bead. With a laser power of 29 mW at the sample plane, the spin speed averaged 158.8±155.5 rpm (mean±standard deviation) and the torque was estimated as 101.9±99.8 pN nm. This optical spin micromotor will be useful in (1) providing a fundamental step toward developing optical-operated mechanical devices, (2) twisting macromolecules, and (3) generating vortex and shear force in medium at nanoscale. © 2000 American Institute of Physics.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions

The kinetics and mechanism of scanned probe oxidation of Si

E. S. Snow, G. G. Jernigan, and P. M. Campbell

Appl. Phys. Lett. 76, 1782 (2000); http://dx.doi.org/10.1063/1.126166 (3 pages) | Cited 47 times

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We report measurements of the kinetics of scanned probe oxidation under conditions of high humidity and pulsed bias. For a hydrophobic Si surface the oxidation rate for short pulse times (∼10 ms) is controlled by the density of H2O molecules in the ambient humidity surrounding the tip-sample interface. At longer pulse times (∼0.1 s) liquid H2O bridges this interface and the maximum oxidation rate increases by a factor of ∼ 104 because of the increased density of H2O molecules. We propose that the rate-limiting step of the oxidation process is the production of O anions from the ambient humidity. © 2000 American Institute of Physics.
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81.65.Mq Oxidation
81.05.Cy Elemental semiconductors
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