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23 Oct 2000

Volume 77, Issue 17, pp. 2629-2769

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Capacitance–voltage and admittance spectroscopy of self-assembled Ge islands in Si

C. Miesner, T. Asperger, K. Brunner, and G. Abstreiter

Appl. Phys. Lett. 77, 2704 (2000); http://dx.doi.org/10.1063/1.1320036 (3 pages) | Cited 19 times

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We investigate the electrical properties of self-assembled Ge islands embedded in Si Schottky diode structures by means of capacitance–voltage measurements and admittance spectroscopy. The Ge islands form at T = 550 °C by self-assembly in the Stranski–Krastanow growth mode with an area density of 4.5×109 cm−2. Their diameter and height are 70 and 6.5 nm, respectively. A linear increase of the thermal activation energy observed in voltage-dependent admittance spectroscopy shows that the ensemble of Ge islands has a low, continuous, averaged density of states. © 2000 American Institute of Physics.
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73.61.Cw Elemental semiconductors
85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.30.+y Surface double layers, Schottky barriers, and work functions

Comparative analysis of zinc-blende and wurtzite GaN for full-band polar optical phonon scattering and negative differential conductivity

C. Bulutay, B. K. Ridley, and N. A. Zakhleniuk

Appl. Phys. Lett. 77, 2707 (2000); http://dx.doi.org/10.1063/1.1320020 (3 pages) | Cited 11 times

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For high-power electronics applications, GaN is a promising semiconductor. Under high electric fields, electrons can reach very high energies where polar optical phonon (POP) emission is the dominant scattering mechanism. So, we undertake a full-band analysis of POP scattering of conduction-band electrons based on an empirical pseudopotential band structure. To uncover the directional variations, we compute POP emission rates along high-symmetry directions for the zinc-blende (ZB) crystal phase of GaN. We also compare the results with those of the wurtzite phase. In general, the POP scattering rates in the zinc-blende phase are lower than the wurtzite phase. Our analysis also reveals appreciable directional dependence, with the Γ–L direction of ZB GaN being least vulnerable to POP scattering, characterized by a scattering time of 11 fs. For both crystal phases, we consider the negative differential conductivity possibilities driven by the negative effective mass part of the band structure. According to our estimation, for the ZB phase the onset of this effect requires fields above ∼ 1 MV/cm. © 2000 American Institute of Physics.
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72.20.Ht High-field and nonlinear effects
72.80.Ey III-V and II-VI semiconductors
63.20.K- Phonon interactions
71.38.-k Polarons and electron-phonon interactions
71.20.Nr Semiconductor compounds
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Atomic beam deposition of lanthanum- and yttrium-based oxide thin films for gate dielectrics

S. Guha, E. Cartier, M. A. Gribelyuk, N. A. Bojarczuk, and M. C. Copel

Appl. Phys. Lett. 77, 2710 (2000); http://dx.doi.org/10.1063/1.1320464 (3 pages) | Cited 134 times

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We report on the electrical and microstructural characteristics of La- and Y-based oxides grown on silicon substrates by ultrahigh vacuum atomic beam deposition, in order to examine their potential as alternate gate dielectrics for Si complementary metal oxide semiconductor technology. We have examined the issues of polycrystallinity and interfacial silicon oxide formation in these films and their effect on the leakage currents and the ability to deposit films with low electrical thickness. We observe that polycrystallinity in the films does not result in unacceptably high leakage currents. We show significant Si penetration in both types of films. We find that the interfacial SiO2 is much thicker at ∼1.5 nm for the Y-based oxide compared to the La-based oxide where the thickness is <0.5 nm. We also show that while the Y-based oxide films show excellent electrical properties, the La based films exhibit a large flat band voltage shift indicative of positive charge in the films. © 2000 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.40.Sz Deposition technology
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.55.-a Thin film structure and morphology
61.66.Bi Elemental solids
61.66.Dk Alloys
68.35.Fx Diffusion; interface formation

Co-incorporation effects of O and Na with CulnS2 thin films

Koichi Fukuzaki, Shigemi Kohiki, Tetsuya Yamamoto, Masaoki Oku, and Takayuki Watanabe

Appl. Phys. Lett. 77, 2713 (2000); http://dx.doi.org/10.1063/1.1320014 (3 pages) | Cited 4 times

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By using x-ray photoelectron spectroscopy we have examined changes in the electronic structure of CuInS2 thin films with co-incorporation of O and Na that raised up the photovoltaic performance of CdS/CuInS2 solar cells. The electron binding energies of both the core levels and valence band for the film with the co-incorporation were smaller by 0.9 eV than those for the film without the co-incorporation. For the co-incorporated film an increase in the spectral intensity of the valence band was observed below 1–6 eV from the Cu 3d10 nonbonding states, and it was due to both the Na s, p-S p hybridization and the In s-Op hybridization. The surface of the co-incorporated film can be expressed as (Cu, Na)In(S, O)2. The (Cu, Na)In(S, O)2 phase is related to the enlarged open-circuit voltage (0.75 eV) of n-CdS/p-CuInS2 solar cells. © 2000 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
71.15.Nc Total energy and cohesive energy calculations
84.60.Jt Photoelectric conversion
79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.20.Ps Other inorganic compounds
61.72.up Other materials
85.40.Ry Impurity doping, diffusion and ion implantation technology

Defect generation in ultrathin silicon dioxide films produced by anode hole injection

D. J. DiMaria

Appl. Phys. Lett. 77, 2716 (2000); http://dx.doi.org/10.1063/1.1320460 (3 pages) | Cited 8 times

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A direct demonstration of defect generation in ultrathin silicon dioxide films due to the transport of holes through this layer is reported. These defects are observed only when the hole current to the cathode of the device exceeds the electron current to the anode. This condition is produced on p-channel field-effect transistors under negative gate-voltage-bias conditions with ultrathin gate oxide layers. These results are related to current reliability models which use anode hole injection and the defects produced to explain destructive breakdown of the oxide layer. © 2000 American Institute of Physics.
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73.61.Ng Insulators
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
71.55.Ht Other nonmetals
85.30.Tv Field effect devices
77.55.-g Dielectric thin films
77.22.Jp Dielectric breakdown and space-charge effects

Anomalous positive charge trapping in thin nitrided oxides under high-field impulse stressing

P. S. Lim and W. K. Chim

Appl. Phys. Lett. 77, 2719 (2000); http://dx.doi.org/10.1063/1.1320041 (3 pages) | Cited 2 times

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An anomalously high density of positive trapped charges was observed in thin (43 Å) nitrided gate oxides subjected to high-field impulse stressing. The hot-hole generation occurs via a regenerative feedback mechanism, with minimal charge relaxation due to the short duration of the impulse stress. This gives rise to an extremely high density of trapped holes that were not observed under direct current stressing conditions. The trapped holes can be easily annealed electrically at room temperature and the annihilation of positive trapped charges is accompanied by a higher number of interface states being created. A better understanding on thin oxide degradation under impulse stressing can help in the choice of a suitable programing/erasing pulse width/amplitude for use in endurance testing of nonvolatile memories. © 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
73.50.Fq High-field and nonlinear effects
85.30.Tv Field effect devices
73.20.-r Electron states at surfaces and interfaces

Effects of prewells on transport in p-type resonant tunneling diodes

R. M. Lewis, H. P. Wei, S. Y. Lin, and J. F. Klem

Appl. Phys. Lett. 77, 2722 (2000); http://dx.doi.org/10.1063/1.1320457 (3 pages) | Cited 1 time

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We investigate the transport of holes through AlAs/In0.10Ga0.90As resonant tunneling diodes which utilize InxGa1−xAs prewells in the emitter with x = 0,0.10, and 0.20. The data show an increase in peak current and bias at resonance and a concurrent increase in the peak-to-valley ratio with increasing x. We explain this enhancement in tunneling as due to confinement (or localization) of charges in the prewell and the formation of direct heavy (light) hole to heavy (light) hole conduction channels as a consequence. © 2000 American Institute of Physics.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.Kk Junction diodes
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.)
73.23.Hk Coulomb blockade; single-electron tunneling
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Giant magnetoimpedance near a metal–insulator transition: Study of Fe in a V2O3 matrix

Sangeetá Kale, S. E. Lofland, S. M. Bhagat, Litty Sebastian, K. Ramesha, J. Gopalakrishnan, S. B. Ogale, Y. H. Li, and J. Garrison

Appl. Phys. Lett. 77, 2725 (2000); http://dx.doi.org/10.1063/1.1319508 (3 pages) | Cited 1 time

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We report microwave absorption measurements as a function of temperature (from 290 to 125 K) and magnetic field (from 0 to 0.3 T) in mm-thick parallelepipeds of sintered V2O3 and V2O3 containing micron-size Fe precipitates. As before, it turns out that near the metal–insulator (MI) transition, the loss exhibits a sharp peak as a function of temperature. On application of a magnetic field, the peak temperature for (V2O3+Fe) changes by a few kelvin, causing a giant magnetoimpedance ( ≈  200% in 0.1 T field) in the neighborhood of the MI transition. © 2000 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.50.Tt Fine-particle systems; nanocrystalline materials
72.60.+g Mixed conductivity and conductivity transitions
75.50.Bb Fe and its alloys
78.70.Gq Microwave and radio-frequency interactions

Magnetoresistance of self-assembled lateral multilayers

E. D. Tober, R. F. Marks, D. D. Chambliss, K. P. Roche, M. F. Toney, A. J. Kellock, and R. F. C. Farrow

Appl. Phys. Lett. 77, 2728 (2000); http://dx.doi.org/10.1063/1.1319514 (3 pages) | Cited 9 times

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The angular-dependent magnetoresistance and magnetization of epitaxial FeηAg1−η self-assembled lateral multilayers (SALMs) grown on Mo(110)/Al2O3(11-20) template layers has been examined for an optimum stoichiometry of η=0.38. The low-temperature anisotropic magnetoresistance (AMR) and low-field magnetoresistance (MR) are measured as a function of field angle for two nearly orthogonal current directions. The SALM structures are observed to display a significant AMR (roughly 1.6% maximum for the entire structure) and a pronounced field-dependent MR with a maximum ΔR/R of 0.88% at 2.7 K. © 2000 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.30.Gw Magnetic anisotropy
75.47.De Giant magnetoresistance
78.20.Ls Magneto-optical effects
78.66.Bz Metals and metallic alloys
75.50.Bb Fe and its alloys

Asymmetry of coercivity dependence on temperature in exchange-biased FeMn/Co bilayers

J. Wang, W. N. Wang, X. Chen, H. W. Zhao, J. G. Zhao, and W. Sh. Zhan

Appl. Phys. Lett. 77, 2731 (2000); http://dx.doi.org/10.1063/1.1319511 (3 pages) | Cited 14 times

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The temperature dependence of the coercivity in biased FeMn/Co bilayers is investigated. An asymmetric behavior of the left and right coercivity with varying temperature is observed. The asymmetry can be understood by taking into account the variation of the spin arrangements in the antiferromagnetic layer. The calculated results are in agreement with the experimental ones qualitatively. All these results suggest that the magnetization reversal mechanisms are different for increasing and decreasing fields. © 2000 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related 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.Et Exchange and superexchange interactions
75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics

Double-exchange ferromagnetism and magnetoresistance in LaMn1−xCuxO3 (x ⩽ 0.3)

Young Sun, Xiaojun Xu, Wei Tong, and Yuheng Zhang

Appl. Phys. Lett. 77, 2734 (2000); http://dx.doi.org/10.1063/1.1320021 (3 pages) | Cited 12 times

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We have studied the magnetic and magnetotransport properties of the perovskite LaMn1−xCuxO3 (x ⩽ 0.3). All of these compounds show ferromagnetism and cluster glass behavior at low temperatures. Though no metallic-insulating transition associated with the ferromagnetic–paramagnetic transition appears, a large magnetoresistance was observed in the ferromagnetic phase. Due to the fact that the Cu ion in these compounds is divalent, the ferromagnetism in LaMn1−xCuxO3 is believed to be consistent with the Mn3+–O–Mn4+ double-exchange mechanism. These results suggest that double exchange and large magnetoresistance can be obtained by direct Mn-site doping. © 2000 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Et Exchange and superexchange interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Magnetoimpedance measurements of ferromagnetic resonance and antiresonance

M. R. Britel, D. Ménard, L. G. Melo, P. Ciureanu, A. Yelon, R. W. Cochrane, M. Rouabhi, and B. Cornut

Appl. Phys. Lett. 77, 2737 (2000); http://dx.doi.org/10.1063/1.1320042 (3 pages) | Cited 22 times

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We report the observation of both ferromagnetic resonance and antiresonance in a magnetic metal using a magnetoimpedance technique. In this experiment, the magnetoimpedance was measured as the frequency was swept from 30 MHz to 11 GHz at constant magnetic fields ranging up to 1.1 kOe (88 kA/m). The sample was an amorphous NiCo-rich soft-magnetic wire with a saturation magnetization sufficiently small to meet both the resonance and antiresonance conditions at frequencies below 10 GHz. A saturation magnetization, very close to that obtained through magnetometry, was deduced using a simultaneous fit to the field dependence of the resonance and antiresonance frequencies. This experiment clearly demonstrates that magnetoimpedance provides a powerful tool for characterizing the intrinsic properties of magnetic metals, with several advantages compared to standard ferromagnetic resonance techniques. © 2000 American Institute of Physics.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Kj Amorphous and quasicrystalline magnetic materials
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.47.De Giant magnetoresistance

Theory of magnetostatic coupling in thin-film rectangular magnetic elements

E. Y. Tsymbal

Appl. Phys. Lett. 77, 2740 (2000); http://dx.doi.org/10.1063/1.1320016 (3 pages) | Cited 9 times

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A theory of magnetostatic coupling in thin-film uniformly magnetized arrays of rectangular magnetic elements is presented. Analytic expressions for the magnetostatic energy and the dipolar fields are derived. The influence of the aspect ratio and the spacing between the elements on the magnetostatic coupling is investigated. It is found that increasing the aspect ratio reduces the critical distance between the elements, above which the magnetostatic inter-element coupling can be neglected. © 2000 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems

Microplow-row lithography and fabrication of submicrometer magnetic structures

S. P. Li, A. Lebib, D. Peyrade, M. Natali, and Y. Chen

Appl. Phys. Lett. 77, 2743 (2000); http://dx.doi.org/10.1063/1.1320462 (3 pages) | Cited 2 times

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This letter describes the use of a microplow-row lithography technique to fabricate wire and dot arrays with submicrometer resolution. Fabrication of patterned magnetic structures with or without resist processing was demonstrated that shows the simplicity and the usefulness of this technique. The performance of the patterned magnetic structures compares favorably with that of similar fabrication by using conventional methods. © 2000 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.05.Bx Metals, semimetals, and alloys
85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
75.50.Cc Other ferromagnetic metals and alloys
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Single-electron transistor strongly coupled to an electrostatically defined quantum dot

W. Lu, A. J. Rimberg, K. D. Maranowski, and A. C. Gossard

Appl. Phys. Lett. 77, 2746 (2000); http://dx.doi.org/10.1063/1.1320455 (3 pages) | Cited 13 times

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A system is described in which an Al-based superconducting single-electron transistor (S–SET) is fabricated directly above an electrostatically defined quantum dot formed in a two-dimensional electron gas. This arrangement allows the coupling capacitance between the S–SET central island and the dot to be comparable to the tunneling capacitances of the dot. As a result, the measured sensitivity of the S–SET referred to charge on the dot is 1.2×10−4 e/math, about an order of magnitude better than previously reported results. The increased sensitivity makes this system ideally suited for broadband measurements such as study of individual tunneling events. © 2000 American Institute of Physics.
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85.25.Cp Josephson devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.23.Hk Coulomb blockade; single-electron tunneling
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
07.68.+m Photography, photographic instruments; xerography
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Structural distortion and ferroelectric properties of SrBi2(Ta1−xNbx)2O9

Y. Shimakawa, Y. Kubo, Y. Tauchi, T. Kamiyama, H. Asano, and F. Izumi

Appl. Phys. Lett. 77, 2749 (2000); http://dx.doi.org/10.1063/1.1319509 (3 pages) | Cited 49 times

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Ferroelectric materials of the SrBi2(Ta1−xNbx)2O9 solid-solution system were synthesized, and their structural and ferroelectric properties were investigated. Atomic displacements of the ions in the (Ta,Nb)O6 octahedron significantly increase as x increases, which leads to more structural distortion of the perovskite-type unit. The Bi2O2 layer, in contrast, is less distorted in SrBi2Nb2O9 than in SrBi2Ta2O9. The contribution of the perovskite-type unit to total ferroelectric polarization is greater in the SrBi2Nb2O9 sample, while that of the Bi2O2 layer is less; consequently, the total calculated polarization slightly increases. The ferroelectric Curie temperature also increases from 300 (SrBi2Ta2O9) to 440 °C(SrBi2Nb2O9). Three short (Ta,Nb)–O bonds in the (Ta,Nb)O6 octahedron, whose lengths are less than 2 Å, have a covalent character, and the substitution of Nb for Ta makes the bonds more covalent. The strong covalent interaction of the (Ta,Nb)–O bonds increases the structural distortion, resulting in the higher ferroelectric Curie temperature and the larger contribution of the perovskite-type unit to the total spontaneous ferroelectric polarization. © 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.B- Phase transitions and Curie point
61.66.Fn Inorganic compounds
77.22.Ej Polarization and depolarization
61.50.Lt Crystal binding; cohesive energy

Ultrathin silicon nitride gate dielectrics prepared by catalytic chemical vapor deposition at low temperatures

Hidekazu Sato, Akira Izumi, and Hideki Matsumura

Appl. Phys. Lett. 77, 2752 (2000); http://dx.doi.org/10.1063/1.1319513 (3 pages) | Cited 7 times

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The feasibility of using ultrathin silicon nitride (SiNx) films, prepared by catalytic chemical vapor deposition (Cat-CVD) method, as an ultrathin gate dielectric is reported. The effects of postdeposition treatments carried out using hydrogen (H2)-decomposed species or NH3-decomposed species formed by catalytic cracking of H2 and NH3 are also studied. A small hysteresis loop is seen in the C–V curve of as-deposited Cat-CVD SiNx films. The leakage current in the case of these films with equivalent oxide thickness (EOT) of 3 nm is slightly larger than that in the conventional thermal SiO2 films of similar EOT. However, it is found that the properties of Cat-CVD SiNx films are markedly improved by the postdeposition H2 or NH3 treatments, that is, the hysteresis loop disappears and the leakage current decreases by three orders of magnitude. © 2000 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Ng Insulators
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
85.30.Tv Field effect devices

Hysteresis loops of ferroelectric bilayers and superlattices

Khian-Hooi Chew, Lye-Hock Ong, Junaidah Osman, and D. R. Tilley

Appl. Phys. Lett. 77, 2755 (2000); http://dx.doi.org/10.1063/1.1320040 (3 pages) | Cited 32 times

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A ferroelectric superlattice with an antiferroelectric interfacial coupling is considered; the same model describes a bilayer with antiferroelectric coupling. By mapping minimum points in the Landau free energy expression and plotting them against the applied electric field, a triple hysteresis loop pattern is obtained. The loop patterns vary between typically ferroelectric and typically antiferroelectric depending on the layer thicknesses and the magnitude of the interfacial-coupling constant. This work suggests the possibility of designing multilayer elements for computer memories with four or more different storage states. © 2000 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization

Tandem injection of charge carriers across a metal-dielectric interface

V. I. Arkhipov and H. Bässler

Appl. Phys. Lett. 77, 2758 (2000); http://dx.doi.org/10.1063/1.1320456 (3 pages) | Cited 7 times

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A tandem mechanism of charge injection from a metal contact into an organic dielectric via an intermediate injection-facilitating layer is considered. It is shown that introducing such a layer can enhance charge injection considerably if the energy of transport states in this layer is in between the Fermi level of the contact and the energy of transport states in the bulk dielectric. The optimum energy of transport states in the intermediate layer and the minimum thickness thereof are calculated. © 2000 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.20.-r Electron states at surfaces and interfaces
85.60.Jb Light-emitting devices
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Time response analysis of ZnSe-based Schottky barrier photodetectors

E. Monroy, F. Vigué, F. Calle, J. I. Izpura, E. Muñoz, and J.-P. Faurie

Appl. Phys. Lett. 77, 2761 (2000); http://dx.doi.org/10.1063/1.1320038 (3 pages) | Cited 18 times

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We report on the characterization of ZnSe- and ZnMgBeSe-based Schottky barrier photodetectors grown on semi-insulating GaAs(001) by molecular-beam epitaxy. The spectral response of the devices shows a very sharp cutoff at variable wavelength, determined by the alloy composition, with a large stop-band rejection. Short-wavelength responsivities of 0.10 A/W and detectivities as high as 1.4×1012 cm Hz1/2 W−1 at −3.5 V bias have been achieved. Their time response behavior has been analyzed in detail. When light is switched off, the devices show photocurrent decays in the microsecond range, consisting of two exponential components with very different time constants. The slower component becomes dominant for high load and reverse bias. This behavior is related to the strong frequency dependence of the device capacitance. © 2000 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes
73.30.+y Surface double layers, Schottky barriers, and work functions
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The effect of As4 pressure on material qualities of AlGaAs/GaAs heterostructures grown on (111)B GaAs substrates

W. Yeo, R. Dimitrov, W. J. Schaff, and L. F. Eastman

Appl. Phys. Lett. 77, 2764 (2000); http://dx.doi.org/10.1063/1.1319535 (3 pages) | Cited 1 time

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High-quality AlGaAs/GaAs heterostructures have been grown on on-axis (111)B GaAs substrates using molecular-beam epitaxy to study the effect of As4 pressure on the material qualities. It was found that the electrical and structural properties were strongly dependent on the As4 pressure. The quality of the heterostructure was investigated by Hall effect, atomic force microscopy, and high-resolution x-ray diffraction measurements. The electron Hall mobility dropped from 7200 and 90 000 cm2/V s to 930 and 1340 cm2/V s at room temperature and 77 K, respectively, as As4 pressure was increased from 4.9×10−6 to 1.1×10−7 Torr. The same trend was observed at the root-mean-square roughness of the AlGaAs/GaAs heterostructures measured by atomic force microscopy, and the intensity and full width at half-maximum of the x-ray diffraction curve. © 2000 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.35.Ct Interface structure and roughness
73.61.Ey III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Nucleation and growth of carbon nanotubes by microwave plasma chemical vapor deposition

Chris Bower, Otto Zhou, Wei Zhu, D. J. Werder, and Sungho Jin

Appl. Phys. Lett. 77, 2767 (2000); http://dx.doi.org/10.1063/1.1319529 (3 pages) | Cited 192 times

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The nucleation and growth of aligned multiwall carbon nanotubes by microwave plasma-enhanced chemical vapor deposition have been studied. The nanotubes nucleate and grow from catalytic cobalt islands on a silicon substrate surface, with both their diameter and length dependent on the size of the cobalt islands. Electron microscopy reveals that the nanotubes grow via a “base growth” mechanism. The nanotubes grow initially at a very rapid and constant rate (∼100 nm/s) that decreases sharply after the catalyst Co particles become fully encapsulated by the nanotubes. We propose a detailed model to explain these experimental observations on nucleation and growth of nanotubes. © 2000 American Institute of Physics.
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81.05.ub Fullerenes and related materials
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
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