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7 May 2012

Volume 100, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 100, 191901 (2012); http://dx.doi.org/10.1063/1.4709436 (4 pages)

Muamer Kadic, Tiemo Bückmann, Nicolas Stenger, Michael Thiel, and Martin Wegener
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Photo-induced changes in fundamental properties of organic solar cells

J. Bhattacharya, R. W. Mayer, M. Samiee, and V. L. Dalal

Appl. Phys. Lett. 100, 193501 (2012); http://dx.doi.org/10.1063/1.4711806 (3 pages) | Cited 3 times

Online Publication Date: 7 May 2012

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We report on the measurement of fundamental properties such as deep defects and hole mobility in poly-3-hexyl-thiophene (P3HT)/[6,6]-phenyl-C60-butyric acid methyl ester(PCBM) solar cells when the cells are exposed to solar radiation without any atmospheric exposure. It is found that the midgap defect density in P3HT and the interface density between P3HT and PCBM increase significantly upon light soaking along with a reduction in hole mobility in P3HT. The increase in defect density leads to a corresponding increase in reverse saturation current of the diode, and the corresponding decrease in open circuit voltage of the cell upon light soaking.
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88.40.jr Organic photovoltaics

Flow and force inducement using micron size dielectric barrier discharge actuators

Justin C. Zito, Ryan J. Durscher, Jignesh Soni, Subrata Roy, and David P. Arnold

Appl. Phys. Lett. 100, 193502 (2012); http://dx.doi.org/10.1063/1.4712068 (4 pages) | Cited 3 times

Online Publication Date: 8 May 2012

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Micron size dielectric barrier discharge actuators, designed for minimal footprint area and weight penalty, show a wall jet up to 2.0 m/s consuming 15 W/m of electrode. A torsional balance measures force up to 3 mN/m of electrode and demonstrates equivalent “thrust effectiveness” (induced force/power) to macroscale actuators. Compared with reported macroscale data, the microscale actuator shows a 31% increase in energy conversion efficiency. Per unit actuator mass, both the force and the velocity induced by microscale actuators show an order of magnitude (22.1 and 18.5 times, respectively) increase over macroscale actuators, making them suitable for distributed flow control applications.
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52.75.-d Plasma devices
52.80.-s Electric discharges

Role of the electric waveform supplying a dielectric barrier discharge plasma actuator

N. Benard and E. Moreau

Appl. Phys. Lett. 100, 193503 (2012); http://dx.doi.org/10.1063/1.4712125 (5 pages) | Cited 1 time

Online Publication Date: 8 May 2012

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The paper compares the influence of different waveforms as input for a dielectric barrier discharge plasma actuator investigated in context of plasma-assisted flow control. The electrical aspects, the plasma morphology, the body force production, and the two-component time-resolved electric wind produced over a single ac period of signal are investigated. Results shown that square waveform is optimal in terms of body force and mean electric wind production, but the velocity fluctuations are enhanced by using a sinusoidal waveform. The time-resolved measurements of the produced velocity demonstrate that the electromechanical conversion mechanism is quasi-linear in the vicinity of the discharge.
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52.80.-s Electric discharges
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena
52.30.-q Plasma dynamics and flow
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.75.-d Plasma devices

Multi-state resistive switching memory with secure information storage in Au/BiFe0.95Mn0.05O3/La5/8Ca3/8MnO3 heterostructure

Y. P. Yao, Y. K. Liu, S. N. Dong, Y. W. Yin, S. W. Yang, and X. G. Li

Appl. Phys. Lett. 100, 193504 (2012); http://dx.doi.org/10.1063/1.4714514 (4 pages) | Cited 1 time

Online Publication Date: 8 May 2012

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The ferroelectric polarization dependent bipolar and conductive filament related unipolar resistive switching behaviors are investigated systematically in Au/BiFe0.95Mn0.05O3/La5/8Ca3/8MnO3 heterostructure. The results show that after conductive filaments are formed, the ferroelectric state previously polarized will keep almost unchanged. By combining the two resistive switching mechanisms together under appropriate programming conditions, a tri-state-like resistive switching behavior is realized, finding effective routes in designing high-density storage. According to these distinctive characteristics, a prototype memory device with secure information storage is properly designed as an example of promising applications.
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85.50.Gk Non-volatile ferroelectric memories

Turn-on spread determines the size of the switching region in an avalanche transistor

Guoyong Duan, Sergey Vainshtein, and Juha Kostamovaara

Appl. Phys. Lett. 100, 193505 (2012); http://dx.doi.org/10.1063/1.4711782 (4 pages) | Cited 1 time

Online Publication Date: 8 May 2012

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It has been shown recently that only a small part of the emitter-base interface in a Si bipolar junction transistor participates in short-pulsing avalanche switching. This lateral current shrinkage attributed to the “winner takes all” effect reduces the transistor switching size from 1600 to ∼100 μm, still remaining much larger than the transistor structure thickness. We show using quasi-3-D transient modelling that the size of the operating perimeter, which is critically important for switching efficiency and device reliability, is determined by competition between lateral turn-on shrinkage and spread. The latter has never been demonstrated in avalanche transistors before.
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85.30.Pq Bipolar transistors
85.30.De Semiconductor-device characterization, design, and modeling

Vertical conduction mechanism of the epitaxial graphene/n-type 4H-SiC heterojunction at cryogenic temperatures

M. J. Tadjer, T. J. Anderson, K. D. Hobart, L. O. Nyakiti, V. D. Wheeler, R. L. Myers-Ward, D. K. Gaskill, C. R. Eddy, Jr., F. J. Kub, and F. Calle

Appl. Phys. Lett. 100, 193506 (2012); http://dx.doi.org/10.1063/1.4712621 (4 pages)

Online Publication Date: 10 May 2012

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Vertical diodes of epitaxial graphene on n− 4H-SiC were investigated. The graphene Raman spectra exhibited a higher intensity in the G-line than the 2D-line, indicative of a few-layer graphene film. Rectifying properties improved at low temperatures as the reverse leakage decreased over six orders of magnitude without freeze-out in either material. Carrier concentration of ∼1016 cm−3 in the SiC remained stable down to 15 K, while accumulation charge decreased and depletion width increased in forward bias. The low barrier height of 0.08 eV and absence of recombination-induced emission indicated majority carrier field emission as the dominant conduction mechanism.
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85.30.Kk Junction diodes

Nm-scale measurements of fast surface potential transients in an AlGaN/GaN high electron mobility transistor

D. W. Cardwell, A. R. Arehart, C. Poblenz, Y. Pei, J. S. Speck, U. K. Mishra, S. A. Ringel, and J. P. Pelz

Appl. Phys. Lett. 100, 193507 (2012); http://dx.doi.org/10.1063/1.4714536 (4 pages) | Cited 3 times

Online Publication Date: 10 May 2012

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Fast, bias-induced, surface potential transients (SPTs) and conductance transients (CTs) were simultaneously measured on an AlGaN/GaN high electron mobility transistor. SPTs measured near the drain-side gate edge and CTs have nearly the same shape and are well-fit with two exponentials having room-temperature time constants of 4.2 ms and 36 ms, likely indicating emission from two trap species. Kelvin probe force microscopy was used to measure SPTs. Electrostatic simulations of SPT amplitudes, which account for the measured probe/sample geometry, are consistent with a uniform trapped surface charge density of 7 × 1012 electrons/cm2 extending 200 nm from the drain-side gate edge.
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85.30.Tv Field effect devices

Encapsulating light-emitting electrochemical cells for improved performance

Amir Asadpoordarvish, Andreas Sandström, Shi Tang, Jimmy Granström, and Ludvig Edman

Appl. Phys. Lett. 100, 193508 (2012); http://dx.doi.org/10.1063/1.4714696 (4 pages) | Cited 3 times

Online Publication Date: 10 May 2012

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We present a functional and scalable encapsulation of light-emitting electrochemical cells (LECs), which results in a measured ambient operation of >400 h at a brightness of >300 cd/m2 with a maximum efficacy of 6 lm/W, and a linearly extrapolated ambient operation of ∼5600 h at >100 cd/m2. Our findings suggest that previous studies have underestimated the practical stability of appropriately encapsulated LECs. We also report that the dominant ambient degradation for non-encapsulated LECs is water-induced delamination of the cathode from the active layer, while encapsulated LECs in contrast are found to decay from spatial variations in the active layer composition.
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85.60.Jb Light-emitting devices

A model determining optimal doping concentration and material’s band gap of tunnel field-effect transistors

William G. Vandenberghe, Anne S. Verhulst, Kuo-Hsing Kao, Kristin De Meyer, Bart Sorée, Wim Magnus, and Guido Groeseneken

Appl. Phys. Lett. 100, 193509 (2012); http://dx.doi.org/10.1063/1.4714544 (4 pages) | Cited 2 times

Online Publication Date: 11 May 2012

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We develop a model for the tunnel field-effect transistor (TFET) based on the Wentzel-Kramer-Brillouin approximation which improves over existing semi-classical models employing generation rates. We hereby introduce the concept of a characteristic tunneling length in direct semiconductors. Based on the model, we show that a limited density of states results in an optimal doping concentration as well as an optimal material’s band gap to obtain the highest TFET on-current at a given supply voltage. The observed optimal-doping trend is confirmed by 2-dimensional quantum-mechanical simulations for silicon and germanium.
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85.30.Tv Field effect devices

Strained In0.53Ga0.47As metal-oxide-semiconductor field-effect transistors with epitaxial based biaxial strain

SangHyeon Kim, Masafumi Yokoyama, Noriyuki Taoka, Ryosho Nakane, Tetsuji Yasuda, Osamu Ichikawa, Noboru Fukuhara, Masahiko Hata, Mitsuru Takenaka, and Shinichi Takagi

Appl. Phys. Lett. 100, 193510 (2012); http://dx.doi.org/10.1063/1.4714770 (3 pages)

Online Publication Date: 11 May 2012

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We have demonstrated epitaxial-based biaxially strained In0.53Ga0.47As metal-oxide-semiconductor field-effect transistors (MOSFETs). Tensile strained In0.53Ga0.47As MOSFETs shows a high peak mobility of 2150 cm2/Vs with the enhancement factor of 3.7 against Si MOSFETs. Furthermore, we have investigated the mobility enhancement mechanisms in the tensile strained In0.53Ga0.47As MOSFETs. It has been found that biaxial tensile strain is effective to enhance the electron mobility in InGaAs MOSFETs by an increase of inversion carrier density, which is caused by the modulation of conduction band minimum.
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85.30.Tv Field effect devices
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