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15 Sep 2008

Volume 93, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 93, 111901 (2008); http://dx.doi.org/10.1063/1.2980583 (3 pages)

W.-J. Lee, E.-A. Choi, J. Bang, B. Ryu, and K. J. Chang
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High-resolution ultrasonic imaging using an etalon detector array

Sheng-Wen Huang, Yang Hou, Shai Ashkenazi, and Matthew O’Donnell

Appl. Phys. Lett. 93, 113501 (2008); http://dx.doi.org/10.1063/1.2982584 (3 pages) | Cited 2 times

Online Publication Date: 15 September 2008

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A photoacoustic imaging system was built and tested to demonstrate the feasibility of high-resolution low-noise ultrasonic imaging based on parallel detection using polymer etalons. Its capability of detecting ultrasound at different elements simultaneously in the optical end was verified by imaging three 49 μm beads. An average noise-equivalent pressure of 3.6 kPa over 50 MHz for 50 μm diameter detection elements in a two-dimensional array with a diameter of 1.35 mm and a detection bandwidth of 75 MHz at –3 dB was measured. These results demonstrate the potential of polymer etalons for high-frame-rate high-resolution three-dimensional photoacoustic and ultrasound pulse-echo imaging.
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43.60.Lq Acoustic imaging, displays, pattern recognition, feature extraction
07.60.Ly Interferometers
42.70.Jk Polymers and organics

Tailoring the gas sensing properties of ZnO thin films through oxygen nonstoichiometry

V. Kobrinsky, A. Rothschild, V. Lumelsky, Y. Komem, and Y. Lifshitz

Appl. Phys. Lett. 93, 113502 (2008); http://dx.doi.org/10.1063/1.2982587 (3 pages) | Cited 9 times

Online Publication Date: 15 September 2008

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A comparative study of the gas sensing properties of n- and p-type ZnO films was performed. The carrier type and concentration tailored by varying the sputtering Ar/O2 mixture were examined by Hall effect measurements. The gas sensing properties were studied by monitoring changes in the dc resistance upon exposure to hydrogen or oxygen. The selectivity of ZnO sensors to these gases was tailored by the carrier type. The origin of the doping and the defect chemistry are evaluated in view of the films’ growth process. The doping effect on the electrical conduction mechanism and sensor performance is discussed.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.61.Ga II-VI semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors

Giant sharp converse magnetoelectric effect from the combination of a piezoelectric transformer with a piezoelectric/magnetostrictive laminated composite

Yaojin Wang, Feifei Wang, Siu Wing Or, Helen Lai Wa Chan, Xiangyong Zhao, and Haosu Luo

Appl. Phys. Lett. 93, 113503 (2008); http://dx.doi.org/10.1063/1.2976329 (3 pages) | Cited 26 times

Online Publication Date: 16 September 2008

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Giant sharp converse magnetoelectric (CME) coefficient of 11.9 G/V is obtained in a heterostructure formed by combining a Rosen-type 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN-PT) piezoelectric single-crystal transformer with a CME laminated composite of a length-magnetized Tb0.3Dy0.7Fe1.92 (Terfenol-D) magnetostrictive alloy plate sandwiched between two thickness-polarized, electroparallel-connected PMN-PT piezoelectric single-crystal plates. The observed giant sharp CME is found to originate from the step-up voltage-gain effect in the transformer and the resonance CME effect in the laminated composite. This heterostructure has promising applications in electrically controlled magnetic memory devices.
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75.80.+q Magnetomechanical effects, magnetostriction
77.65.-j Piezoelectricity and electromechanical effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Voltage polarity dependent low-power and high-speed resistance switching in CoO resistance random access memory with Ta electrode

Hisashi Shima, Fumiyoshi Takano, Hidenobu Muramatsu, Hiro Akinaga, Yukio Tamai, Isao H. Inque, and Hidenori Takagi

Appl. Phys. Lett. 93, 113504 (2008); http://dx.doi.org/10.1063/1.2982426 (3 pages) | Cited 32 times

Online Publication Date: 18 September 2008

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Structural and resistance switching properties were investigated in the CoO resistance random access memory (RRAM) with the Ta electrode. The intermediate layer consisting of Co and Ta oxides was confirmed at the interface by the transmission electron microscopy and electron energy loss spectroscopy. The great affinity with oxygen in Ta together with a high resistivity of the Ta oxide improves the operational performance of RRAM. The controllability of the resistance after forming and the low-current operation property were substantially improved by using the load resistor connected in series with CoO RRAM with the Ta electrode. The reset current less than 0.2 mA and the switching speed faster than 20 ns were demonstrated.
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84.30.Sk Pulse and digital circuits

Oscillator circuit based on a single organic transistor

René Dost, Sumon K. Ray, Arindam Das, and Martin Grell

Appl. Phys. Lett. 93, 113505 (2008); http://dx.doi.org/10.1063/1.2987425 (3 pages) | Cited 1 time

Online Publication Date: 18 September 2008

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We design and demonstrate an oscillator circuit based on feedback and controlled by a single organic transistor. Oscillations are assisted by standard operational amplifiers. The oscillator frequency f partly depends on the parameters of the circuit, but also on the transistor’s channel length and charge carrier mobility. Monitoring f provides a fast and simple tool in following the change in semiconductor mobility under changing environmental conditions. We demonstrate the application of the circuit for cheap, portable organic transistor-based odor sensors.
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84.30.Ng Oscillators, pulse generators, and function generators
05.45.Xt Synchronization; coupled oscillators
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Tv Field effect devices

Comparison of n-type and p-type GaAs oxide growth and its effects on frequency dispersion characteristics

C. L. Hinkle, A. M. Sonnet, M. Milojevic, F. S. Aguirre-Tostado, H. C. Kim, J. Kim, R. M. Wallace, and E. M. Vogel

Appl. Phys. Lett. 93, 113506 (2008); http://dx.doi.org/10.1063/1.2987428 (3 pages) | Cited 24 times

Online Publication Date: 19 September 2008

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The electrical characteristics of n- and p-type gallium arsenide (GaAs) capacitors show a striking difference in the “accumulation” capacitance frequency dispersion. This difference has been attributed by some to a variation in the oxide growth, possibly due to photoelectrochemical properties of the two substrates. We show that the oxide growth on n- and p-type GaAs substrates is identical when exposed to identical environmental and chemical conditions while still maintaining the diverse electrical characteristics. The difference in electron and hole trap time constants is suggested as the source of the disparity of the frequency dispersion for n-type versus p-type GaAs devices.
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81.05.Ea III-V semiconductors
81.65.Mq Oxidation
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
82.50.-m Photochemistry
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Structural and optical properties of Cr-doped semi-insulating GaN epilayers

F. Mei, K. M. Wu, Y. Pan, T. Han, C. Liu, J. W. Gerlach, and B. Rauschenbach

Appl. Phys. Lett. 93, 113507 (2008); http://dx.doi.org/10.1063/1.2988000 (3 pages) | Cited 1 time

Online Publication Date: 19 September 2008

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The properties of Cr-doped GaN epilayers grown by rf-plasma-assisted molecular beam epitaxy were studied. The deep acceptor nature of Cr was used to grow semi-insulating GaN epilayers on sapphire substrates for electronic device applications. The room-temperature (RT) sheet resistivity of the epilayers reached 1010 Ω/square. The activation energy of dark conductivity was about 0.48 eV. Step-graded AlxGa1−xN/GaN (x = 0.3−0.2) superlattices (SLs) were designed to filter dislocations. Transmission electron microscopy images showed that the SLs can dramatically reduce dislocation density. Al0.35Ga0.65N/GaN heterostructure grown on Cr-doped semi-insulating GaN epilayer exhibited a RT mobility of 960 cm2/V s and sheet carrier density of 2.1×1013 cm−2.
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68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors
73.50.Pz Photoconduction and photovoltaic effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
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