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28 Mar 2005

Volume 86, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 86, 131114 (2005); http://dx.doi.org/10.1063/1.1889243 (3 pages)

R. Chan, M. Feng, N. Holonyak, and G. Walter
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Low-voltage pentacene thin-film transistors with Ta2O5 gate insulators and their reversible light-induced threshold voltage shift

Yan Liang, Guifang Dong, Yan Hu, Liduo Wang, and Yong Qiu

Appl. Phys. Lett. 86, 132101 (2005); http://dx.doi.org/10.1063/1.1896099 (3 pages) | Cited 13 times

Online Publication Date: 21 March 2005

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We have fabricated pentacene thin-film transistors using Ta2O5 films prepared by magnetron reactive sputtering as gate insulators. These transistors exhibit good electrical characteristics at an operating voltage as low as 5 V, with a field-effect mobility of 0.32 cm2/Vs, an on∕off ratio of 104, and a subthreshold slope of 0.5 V/decade. We have also investigated the optical properties of these transistors and observed a reversible light-induced threshold voltage shift. Under illumination, the threshold voltage shifts towards the positive direction while the field-effect mobility and on∕off ratio remain almost unchanged. In the dark, however, the threshold voltage can slowly be restored to its original state. At a gate voltage of −5 V, the transistors show a broadband responsivity of 3.7 A/W after illumination at 60 μW/cm2 for 10 min.
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85.30.Tv Field effect devices
81.15.Cd Deposition by sputtering
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
77.55.-g Dielectric thin films

Resonance-tunneling-assisted emission enhancement in green light-emitting diodes with nanocraters formed in InGaN/GaN quantum-well active layers

Jae Ho Song, G. Hugh Song, Jhang W. Lee, Young-Woo Ok, Tae-Yeon Seong, Oleg Laboutin, Paul Deluca, and H. K. Choi

Appl. Phys. Lett. 86, 132102 (2005); http://dx.doi.org/10.1063/1.1890475 (3 pages) | Cited 1 time

Online Publication Date: 21 March 2005

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Data are presented on the resonant tunneling-related abrupt redshift observed in the temperature-dependent electroluminescence spectra of high-brightness InGaN/GaN multi-quantum-well green light-emitting diodes (LEDs). It is found that the redshift arises mostly between 120 and 150 K, and brighter LEDs yield larger redshifts. These results are well explained by the proposed nanocrater model which comprises a Ga-rich quantum barrier surrounding the In-rich quantum-dot-like localized state. Intensity analysis manifests that the resonant tunneling from the quantum-well to the nanocrater-shaped localized states induces such an abrupt energy shift and enhances the room-temperature emission.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
78.60.Fi Electroluminescence
73.40.Gk Tunneling

Impact of interface structure on Schottky-barrier height for Ni/ZrO2(001) interfaces

Y. F. Dong, S. J. Wang, J. W. Chai, Y. P. Feng, and A. C. H. Huan

Appl. Phys. Lett. 86, 132103 (2005); http://dx.doi.org/10.1063/1.1891285 (3 pages) | Cited 24 times

Online Publication Date: 21 March 2005

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The Schottky-barrier heights for the Ni and ZrO2 interfaces have been determined using the x-ray photoemission method. Depending on the surface treatment of ZrO2, the variation of Schottky-barrier heights at Ni/ZrO2 interfaces was found as large as 0.76±0.10 eV. The p-type Schottky-barrier height for the oxygen-rich (oxygen-deficient) interface was measured to be 2.60 eV (3.36 eV). First-principles calculations provide a microscopic explanation of such variation, which was attributed to the different interface dipole formed by interfacial Ni–O, Ni–Zr bonds, or oxygen vacancies.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
68.35.Ct Interface structure and roughness
79.60.Jv Interfaces; heterostructures; nanostructures
61.72.J- Point defects and defect clusters
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
73.20.At Surface states, band structure, electron density of states

Deep-level optical spectroscopy investigation of N-doped TiO2 films

Yoshitaka Nakano, Takeshi Morikawa, Takeshi Ohwaki, and Yasunori Taga

Appl. Phys. Lett. 86, 132104 (2005); http://dx.doi.org/10.1063/1.1896450 (3 pages) | Cited 72 times

Online Publication Date: 24 March 2005

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N-doped TiO2 films were deposited on n+-GaN/Al2O3 substrates by reactive magnetron sputtering and subsequently crystallized by annealing at 550 °C in flowing N2 gas. The N-doping concentration was ∼ 8.8%, as determined from x-ray photoelectron spectroscopy measurements. Deep-level optical spectroscopy measurements revealed two characteristic deep levels located at ∼ 1.18 and ∼ 2.48 eV below the conduction band. The 1.18 eV level is probably attributable to the O vacancy state and can be active as an efficient generation-recombination center. Additionally, the 2.48 eV band is newly introduced by the N doping and contributes to band-gap narrowing by mixing with the O 2p valence band.
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81.05.Hd Other semiconductors
61.72.up Other materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Cd Deposition by sputtering
61.72.Cc Kinetics of defect formation and annealing
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.72.J- Point defects and defect clusters
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.72.S- Impurities in crystals
73.61.Le Other inorganic semiconductors

Strain relaxation and oxygen superstructure modulation in epitaxial Sr4Fe6O13±δ films

J. Santiso, J. A. Pardo, C. Solís, G. Garcia, A. Figueras, M. D. Rossell, and G. Van Tendeloo

Appl. Phys. Lett. 86, 132105 (2005); http://dx.doi.org/10.1063/1.1886264 (3 pages) | Cited 2 times

Online Publication Date: 25 March 2005

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The compressive strain induced in epitaxial Sr4Fe6O13±δ (SFO) films of different thicknesses grown on SrTiO3 substrates is partially released by the modulation of the incommensurate oxygen superstructure along the a-axis parallel to the substrate [q = αam*, superspace group Xmmm(α00)0s0]. The modulation α value varies proportionally to the in-plane a-parameter in a continuous range from 0.41, for fully strained thin films of about 20–30 nm, to 0.44 for partially-relaxed thicker films of about 280 nm. This mechanism is responsible for the observed slow relaxation of the cell structure upon the film thickness increase in comparison with an equilibrium misfit dislocation-mediated relaxation.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
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