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8 Jun 2009

Volume 94, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 94, 233101 (2009); http://dx.doi.org/10.1063/1.3148782 (3 pages)

E. Moyen, M. Macé, G. Agnus, A. Fleurence, T. Maroutian, F. Houzé, A. Stupakiewicz, L. Masson, B. Bartenlian, W. Wulfhekel, P. Beauvillain, and M. Hanbücken
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Carrier compensation by deep levels in Zn1−xMgxO/sapphire

A. Hierro, G. Tabares, J. M. Ulloa, E. Muñoz, A. Nakamura, T. Hayashi, and J. Temmyo

Appl. Phys. Lett. 94, 232101 (2009); http://dx.doi.org/10.1063/1.3149699 (3 pages) | Cited 10 times

Online Publication Date: 8 June 2009

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A systematic analysis of the deep level spectrum in the lower half of the bandgap of Au–Zn1−xMgxO (0.056<x<0.18) Schottky diodes is presented. Two deep levels are observed at Ev+580 and Ev+280 meV regardless of the bandgap energy with trap concentrations linearly increasing with the Mg content. The Ev+280 meV trap concentration becomes as high as 1.01×1018 cm−3 at 18% Mg, partially compensating the films and causing a decrease from 8.02×1016 to 1.27×1016 cm−3 in the net electron concentration and an increase by three orders of magnitude in the diode series resistance due to electron trapping.
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71.55.Gs II-VI semiconductors
85.30.Kk Junction diodes
72.80.Jc Other crystalline inorganic semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Nonadiabatic small polaron tunneling conduction in reduced Cr-doped SrTiO3−δ thin films

Bach Thang Phan and Jaichan Lee

Appl. Phys. Lett. 94, 232102 (2009); http://dx.doi.org/10.1063/1.3151957 (3 pages) | Cited 6 times

Online Publication Date: 9 June 2009

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We investigated the electrical conduction and dielectric relaxation of reduced Cr-doped SrTiO3−δ thin films. The electrical conduction behavior indicates the formation of small polarons in oxygen deficient Cr-doped SrTiO3−δ thin films. The associated dielectric relaxation further indicates nonadiabatic small polaron tunneling conduction. A strong electron-phonon interaction is identified based on the large polaron coupling constant, α ≈ 28(α⪢4).
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77.22.Gm Dielectric loss and relaxation
73.61.Ng Insulators
71.38.-k Polarons and electron-phonon interactions
77.55.-g Dielectric thin films
63.20.kd Phonon-electron interactions
73.40.Gk Tunneling

Frequency-dependent complex conductivity of an organic thin-film transistor

Daniel R. Lenski, Adrian Southard, and Michael S. Fuhrer

Appl. Phys. Lett. 94, 232103 (2009); http://dx.doi.org/10.1063/1.3153159 (3 pages) | Cited 3 times

Online Publication Date: 10 June 2009

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We measure the complex impedance between source/drain electrodes and the gate electrode of a pentacene thin-film transistor (TFT) at frequencies 50 Hz<ω/2π<20 kHz. Modeling the TFT as a distributed resistor and capacitor (RC) network (RC transmission line), we find that the data cannot be explained by a model including only a real, frequency-independent sheet conductivity. Instead, we use the RC transmission line model to extract the frequency-dependent complex sheet conductivity σ(ω) = σ′(ω)+jσ″(ω) of the pentacene film. At high frequencies, σ(ω) increases with frequency, σ′(ω) and σ″(ω) become similar in magnitude, and the on/off ratio is significantly reduced.
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85.30.Tv Field effect devices

Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures

Elmer Estacio, Minh Hong Pham, Satoru Takatori, Marilou Cadatal-Raduban, Tomoharu Nakazato, Toshihiko Shimizu, Nobuhiko Sarukura, Armando Somintac, Michael Defensor, Fritz Christian B. Awitan, Rafael B. Jaculbia, Arnel Salvador, and Alipio Garcia

Appl. Phys. Lett. 94, 232104 (2009); http://dx.doi.org/10.1063/1.3148670 (3 pages) | Cited 7 times

Online Publication Date: 11 June 2009

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We report on the intense terahertz emission from InAs/GaAs quantum dot (QD) structures grown by molecular beam epitaxy. Results reveal that the QD sample emission was as high as 70% of that of a p-type InAs wafer, the most intense semiconductor emitter to date. Excitation wavelength studies showed that the emission was due to absorption in strained undoped GaAs, and corresponds to a two order-of-magnitude enhancement. Moreover, it was found that multilayer QDs emit more strongly compared with a single layer QD sample. At present, we ascribe the intense radiation to huge strain fields at the InAs/GaAs interface.
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78.67.Hc Quantum dots
81.07.Ta Quantum dots
78.70.Gq Microwave and radio-frequency interactions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.47.D- Time resolved spectroscopy (>1 psec)

Electron transport in carbon nanotube-silicon heterodimensional heterojunction array: An experimental investigation

Teng-Fang Kuo, Marian B. Tzolov, Daniel A. Straus, and Jimmy Xu

Appl. Phys. Lett. 94, 232105 (2009); http://dx.doi.org/10.1063/1.3151858 (3 pages) | Cited 4 times

Online Publication Date: 11 June 2009

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Current-voltage experiments on a highly ordered array of carbon nanotubes interfaced with silicon reveal interesting features arising from the regular array of heterojunctions between one-dimensional (1D) and three-dimensional materials. At high temperature, the vertically aligned and ordered nanotubes behave as an array of point junction contacts to the silicon below, which merge into a planar junction as temperature decreases. This model is further supported by the observation of signature space charge limited conduction, whose origin is attributed to deep levels in the silicon substrate and to the strong field enhancement due to the quasi-1D nanotubes.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Ht High-field and nonlinear effects
68.47.Fg Semiconductor surfaces
73.63.Fg Nanotubes
61.46.Fg Nanotubes

Control and elimination of nucleation-related defects in GaP/Si(001) heteroepitaxy

T. J. Grassman, M. R. Brenner, S. Rajagopalan, R. Unocic, R. Dehoff, M. Mills, H. Fraser, and S. A. Ringel

Appl. Phys. Lett. 94, 232106 (2009); http://dx.doi.org/10.1063/1.3154548 (3 pages) | Cited 21 times

Online Publication Date: 11 June 2009

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GaP films were grown on offcut Si(001) substrates using migration enhanced epitaxy nucleation followed by molecular beam epitaxy, with the intent of controlling and eliminating the formation of heterovalent (III-V/IV) nucleation-related defects—antiphase domains, stacking faults, and microtwins. Analysis of these films via reflection high-energy electron diffraction, atomic force microscopy, and both cross-sectional and plan-view transmission electron microscopies indicate high-quality GaP layers on Si that portend a virtual GaP substrate technology, in which the aforementioned extended defects are simultaneously eliminated. The only prevalent remaining defects are the expected misfit dislocations due to the GaP–Si lattice mismatch.
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68.55.ag Semiconductors
61.72.Nn Stacking faults and other planar or extended defects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Ps Atomic force microscopy (AFM)

Temperature dependence of microwave-induced magnetoresistance oscillation in two-dimensional electron systems

X. L. Lei and S. Y. Liu

Appl. Phys. Lett. 94, 232107 (2009); http://dx.doi.org/10.1063/1.3136757 (3 pages) | Cited 3 times

Online Publication Date: 12 June 2009

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Microwave-induced magnetoresistance oscillations in two-dimensional electron systems are examined from a photon-assisted transport scheme with short-range impurity scatterings. Analytical results at high filling factors strongly support early considerations and the recent experimental observation that the temperature dependence of the oscillation amplitude is exponential and originates primarily from the single-particle lifetime.
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72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)

Study of hole accumulation in individual germanium quantum dots in p-type silicon by off-axis electron holography

Luying Li, Sutharsan Ketharanathan, Jeff Drucker, and Martha R. McCartney

Appl. Phys. Lett. 94, 232108 (2009); http://dx.doi.org/10.1063/1.3154524 (3 pages) | Cited 3 times

Online Publication Date: 12 June 2009

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Epitaxial germanium quantum dots (QDs) embedded in boron-doped silicon have been studied using off-axis electron holography to estimate the number of holes associated with a single QD. Holes were confined near the base of the pyramidal, 25-nm-wide Ge QDs. The resulting estimate of charge density was 0.03 holes/nm3 which corresponded to about 30 holes localized to the investigated dot. For comparison, the average number of holes confined to each Ge dot was found to be about 40, using a capacitance-voltage measurement. The difference emphasizes the value of measuring charges confined to individual nm-scale regions of a heterogeneous sample.
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73.63.Kv Quantum dots
73.61.Cw Elemental semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Transport properties of a quantum dot in quantum Hall regimes probed by a single-electron transistor

J. C. Chen, Ming-Yang Li, T. Ueda, and S. Komiyama

Appl. Phys. Lett. 94, 232109 (2009); http://dx.doi.org/10.1063/1.3155205 (3 pages) | Cited 2 times

Online Publication Date: 12 June 2009

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Coulomb blockade oscillations in a semiconductor quantum dot (QD) with two confined Landau levels are investigated by probing a current through a single-electron transistor (SET) fabricated directly on top of the QD. The intradot tunneling events between the compressible regions in the dot are mapped out by measuring SET currents. Our results demonstrate that a SET can be an excellent electrometer that is extremely responsive to the local individual electron tunneling events in a closed electronic system.
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85.35.Gv Single electron devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.43.Jn Tunneling
73.63.Kv Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling
85.35.Ds Quantum interference devices
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