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5 Jul 2010

Volume 97, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 97, 013301 (2010); http://dx.doi.org/10.1063/1.3458867 (3 pages)

M. Uno, Y. Hirose, T. Uemura, K. Takimiya, Y. Nakazawa, and J. Takeya
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Nitrogen doped MgxZn1−xO/ZnO single heterostructure ultraviolet light-emitting diodes on ZnO substrates

K. Nakahara, S. Akasaka, H. Yuji, K. Tamura, T. Fujii, Y. Nishimoto, D. Takamizu, A. Sasaki, T. Tanabe, H. Takasu, H. Amaike, T. Onuma, S. F. Chichibu, A. Tsukazaki, A. Ohtomo, et al.

Appl. Phys. Lett. 97, 013501 (2010); http://dx.doi.org/10.1063/1.3459139 (3 pages) | Cited 48 times

Online Publication Date: 6 July 2010

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We have grown nitrogen-doped MgxZn1−xO:N films on Zn-polar ZnO single crystal substrates by molecular beam epitaxy. As N-sources, we employed NO-plasma or NH3 gas itself. As x increased, optimum growth temperature window for smooth film morphology shifted to higher temperatures, while maintaining high N-concentration ( ∼ 1×1019 cm−3). The heterosructures of MgxZn1−xO:N (0.1 ≤ x ≤ 0.4)/ZnO were fabricated into light emitting diodes of 500-μm-diameter. We observed ultraviolet near-band-edge emission (λ ∼ 382 nm) with an output power of 0.1 μW for a NO-plasma-doped LED and 70 μW for a NH3-doped one at a bias current of 30 mA.
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85.60.Jb Light-emitting devices

Inverted Al0.25Ga0.75N/GaN ultraviolet p-i-n photodiodes formed on p-GaN template layer grown by metalorganic vapor phase epitaxy

Kuo-Hua Chang, Jinn-Kong Sheu, Ming-Lun Lee, Shang-Ju Tu, Chih-Ciao Yang, Huan-Shao Kuo, J. H. Yang, and Wei-Chih Lai

Appl. Phys. Lett. 97, 013502 (2010); http://dx.doi.org/10.1063/1.3462294 (3 pages) | Cited 4 times

Online Publication Date: 7 July 2010

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Inverted Al0.25Ga0.75N/GaN ultraviolet (UV) p-i-n photodiodes (PDs) were grown by selective-area regrowth on p-GaN template. The inverted devices with low-resistivity n-type AlGaN top-contact layers exhibited a typical zero-bias peak responsivity of 66.7 mA/W at 310 nm corresponding to the external quantum efficiency of 26.6%. The typical UV-to-visible (310/400 nm) spectral rejection ratio at zero-bias was over three orders of magnitude. The differential resistance and detectivity were obtained at approximately 6.2×1012 Ω and 3.4×1013 cm Hz1/2 W−1, respectively. Compared with conventional AlGaN/GaN-based UV p-i-n PDs, the proposed device structure can potentially achieve solar-blind AlGaN/GaN-based p-i-n PDs with low-aluminum content or aluminum-free p-contact layer and reduce excessive tensile strain due to the lattice mismatch between AlGaN and GaN layers.
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85.60.Dw Photodiodes; phototransistors; photoresistors

p-Si nanowires/SiO2/n-ZnO heterojunction photodiodes

Chun-Ying Huang, Ying-Jay Yang, Ju-Ying Chen, Chun-Hsiung Wang, Yang-Fang Chen, Lu-Sheng Hong, Chie-Sheng Liu, and Chia-Yin Wu

Appl. Phys. Lett. 97, 013503 (2010); http://dx.doi.org/10.1063/1.3462319 (3 pages) | Cited 13 times

Online Publication Date: 8 July 2010

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Influence of a SiO2 ultrathin film on n-ZnO/p-silicon nanowires photodiodes has been investigated. With a SiO2 thin layer, the diode characteristics can be significantly improved, which exhibits high responsivity under a reverse bias. Based on the electron conversion efficiency measurement, we show that the ultrathin SiO2 layer with positive fixed charges not only acts as a hole blocking layer but also helps the photogenerated electrons to tunnel through the barrier. In addition, the SiO2 layer can effectively passivate the defects generated by wet etching process. It is expected that our approach can be extended to many other nanoscale heterojunction devices.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.De Semiconductor-device characterization, design, and modeling
81.65.Rv Passivation
81.65.Cf Surface cleaning, etching, patterning
85.60.Bt Optoelectronic device characterization, design, and modeling
85.30.Kk Junction diodes

Interface defect-assisted single electron charging (and discharging) dynamics in Ge nanocrystals memories

J. S. de Sousa, R. Peibst, G. A. Farias, J.-P. Leburton, and K. R. Hofmann

Appl. Phys. Lett. 97, 013504 (2010); http://dx.doi.org/10.1063/1.3455899 (3 pages) | Cited 1 time

Online Publication Date: 8 July 2010

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The charging and discharging dynamics of Ge nanocrystal memories is measured and compared with a realistic quantum mechanical model that is able to reproduce qualitatively the overall device behavior. Quantitatively, the charging (discharging) dynamics is faster (slower) than predicted by calculations. To explain the discrepancies, we propose the quantum confined nanocrystal states are responsible for collecting the incoming electrons, but some of them are captured by defects in the nanocrystal surface. The potential created by the filled defects modify the spatial distribution of the nanocrystal wave functions, enhancing their penetration in the tunneling oxide and increasing the incoming transition rates. In the discharging process, the electrons confined in the nanocrystal states escape initially, while the ones in the defects have to be thermally excited to the nanocrystals states in order to tunnel out, slowing down the escape of the last few electrons.
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84.30.Sk Pulse and digital circuits
85.30.-z Semiconductor devices

Nonlinear pH sensitivity of molecular modified transistors

Hila Einati, Roman Novitski, and Yosi Shacham-Diamand

Appl. Phys. Lett. 97, 013505 (2010); http://dx.doi.org/10.1063/1.3462318 (3 pages)

Online Publication Date: 9 July 2010

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The integration of organic self-assembled monolayers (SAMs) in electronic devices is very attractive since they offer high flexibility in design and applications. This paper models the operation of functionalized field effect transistor with a liquid gate. The model explains the nonlinear response to pH variations in SAM-field effect devices. The organic monolayers have low density of sites in comparison to inorganic layers; furthermore, the transistor sensitivity to pH is low and dramatically influenced by the Helmholtz capacitance. It was proven that the dissociation constants have a strong effect on the characteristics of organic field effect device.
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85.30.Tv Field effect devices
82.45.Mp Thin layers, films, monolayers, membranes
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Integration of HfO2 on Si/SiC heterojunctions for the gate architecture of SiC power devices

P. M. Gammon, A. Pérez-Tomás, M. R. Jennings, O. J. Guy, N. Rimmer, J. Llobet, N. Mestres, P. Godignon, M. Placidi, M. Zabala, J. A. Covington, and P. A. Mawby

Appl. Phys. Lett. 97, 013506 (2010); http://dx.doi.org/10.1063/1.3462932 (3 pages) | Cited 1 time

Online Publication Date: 9 July 2010

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In this paper we present a method for integrating HfO2 into the SiC gate architecture, through the use of a thin wafer bonded Si heterojunction layer. Capacitors consisting of HfO2 on Si, SiC, Si/SiC, and SiO2/SiC have been fabricated and electrically tested. The HfO2/Si/SiC capacitors minimize leakage, with a breakdown electric field of 3.5 MV/cm through the introduction of a narrow band gap semiconductor between the two wide band gap materials. The Si/SiC heterojunction was analyzed using transmission electron microscopy, energy dispersive x-ray, and Raman analysis, proving that the interface is free of contaminants and that the Si layer remains unstressed.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
85.30.Tv Field effect devices
78.30.Am Elemental semiconductors and insulators
85.30.De Semiconductor-device characterization, design, and modeling
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Planar Hall effect bridge magnetic field sensors

A. D. Henriksen, B. T. Dalslet, D. H. Skieller, K. H. Lee, F. Okkels, and M. F. Hansen

Appl. Phys. Lett. 97, 013507 (2010); http://dx.doi.org/10.1063/1.3460290 (3 pages) | Cited 7 times

Online Publication Date: 9 July 2010

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Until now, the planar Hall effect has been studied in samples with cross-shaped Hall geometry. We demonstrate theoretically and experimentally that the planar Hall effect can be observed for an exchange-biased ferromagnetic material in a Wheatstone bridge topology and that the sensor signal can be significantly enhanced by a geometric factor. For the samples in the present study, we demonstrate an enhancement of the sensor output by a factor of about 100 compared to cross-shaped sensors. The presented construction opens a new design and application area of the planar Hall effect, which we term planar Hall effect bridge sensors.
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85.75.Ss Magnetic field sensors using spin polarized transport
02.40.-k Geometry, differential geometry, and topology
07.55.Ge Magnetometers for magnetic field measurements
85.75.Nn Hybrid Hall devices
06.30.Ka Basic electromagnetic quantities
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