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15 Aug 2005

Volume 87, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 87, 073101 (2005); http://dx.doi.org/10.1063/1.2010598 (3 pages)

Ji Ung Lee
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Coherent control of a flux qubit by phase-shifted resonant microwave pulses

Tatsuya Kutsuzawa, Hirotaka Tanaka, Shiro Saito, Hayato Nakano, Kouichi Semba, and Hideaki Takayanagi

Appl. Phys. Lett. 87, 073501 (2005); http://dx.doi.org/10.1063/1.2010610 (3 pages) | Cited 9 times

Online Publication Date: 9 August 2005

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The quantum state of a flux qubit was successfully pulse controlled by using a resonant microwave. We observed Ramsey fringes by applying a pair of phase-shifted π/2 microwave pulses without introducing detuning. With this method, the qubit state can be rotated on an arbitrary axis in the x‐y plane of the Bloch sphere in a rotating frame. We successfully observed qubit Larmor precession stroboscopically with an angular velocity of 2π×11.4G rad/s. In combination with Rabi pulses, this method enables us to achieve full control of single qubit rotation with shorter operation time.
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03.67.Lx Quantum computation architectures and implementations
85.25.Cp Josephson devices
85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits

Sidewalls contribution in integrated three-dimensional Sr0.8Bi2.2Ta2O9-based ferroelectric capacitors

N. Menou, Ch. Turquat, V. Madigou, Ch. Muller, L. Goux, J. Lisoni, M. Schwitters, and D. J. Wouters

Appl. Phys. Lett. 87, 073502 (2005); http://dx.doi.org/10.1063/1.2010612 (3 pages) | Cited 8 times

Online Publication Date: 9 August 2005

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As compared to usual planar capacitors, three-dimensional (3D) ferroelectric capacitors display a large polarization increase due to the additional electrical contribution of the capacitor sidewalls. However, in 3D capacitors the polarization increase with respect to the planar geometry is lower than expected. To uncover the origin of this discrepancy, the microstructure of 3D Sr0.8Bi2.2Ta2O9-based (SBT) capacitors was studied. First, high-resolution synchrotron x-ray diffraction has found a unit cell expansion of the SBT phase in the capacitor sidewalls. From local chemical analyses, this lattice distortion has been correlated to composition variations in this region. These microstructural changes are due to the peculiar topography of the etched bottom electrode and to the variety of layers in contact with the SBT film, which can explain the nonoptimized polarization in 3D capacitors.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Open circuit voltage improvement of high-deposition-rate microcrystalline silicon solar cells by hot wire interface layers

Y. Mai, S. Klein, R. Carius, H. Stiebig, X. Geng, and F. Finger

Appl. Phys. Lett. 87, 073503 (2005); http://dx.doi.org/10.1063/1.2011771 (3 pages) | Cited 34 times

Online Publication Date: 9 August 2005

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Significant improvement in open circuit voltage and fill factor was achieved for microcrystalline silicon (μc‐Si:H) solar cells deposited by plasma-enhanced chemical vapor deposition (PECVD) by the incorporation of an intrinsic μc‐Si:H p/i buffer layer fabricated by hot-wire (HW) CVD. The improved p/i interface quality, likely due to the ion-free deposition on the p layers in the HWCVD process, was concluded from a considerably enhanced blue light response in such solar cells. Using this buffer layer concept allows the authors to apply high deposition rate PECVD processes for the μc‐Si:H i layer material, yielding a high efficiency of 10.3% for a single junction μc‐Si:H solar cell.
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84.60.Jt Photoelectric conversion
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

High drain current density and reduced gate leakage current in channel-doped AlGaN/GaN heterostructure field-effect transistors with Al2O3/Si3N4 gate insulator

Narihiko Maeda, Chengxin Wang, Takatomo Enoki, Toshiki Makimoto, and Takehiko Tawara

Appl. Phys. Lett. 87, 073504 (2005); http://dx.doi.org/10.1063/1.2012535 (3 pages) | Cited 12 times

Online Publication Date: 9 August 2005

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Channel-doped AlGaN/GaN heterostructure field-effect transistors (HFETs) with metal-insulator-semiconductor (MIS) structures have been fabricated to obtain the high drain current density and reduced gate leakage current. A thin bilayer dielectric of Al2O3(4 nm)/Si3N4(1 nm) was used as the gate insulator, to simultaneously take advantage of the high-quality interface between Si3N4 and AlGaN, and high resistivity and a high dielectric constant of Al2O3. A MIS HFET with a gate length of 1.5 μm has exhibited a record high drain current density of 1.87 A/mm at a gate voltage (Vg) of +3 V, which is ascribed to a high applicable Vg and a very high two-dimensional electron gas (2DEG) density of 2.6×1013 cm−2 in the doped channel. The gate leakage current was reduced by two or three orders of magnitude, compared with that in normal HFETs without a gate insulator. The transconductance (gm) was 168 mS/mm, which is high in the category of the MIS structure. Channel-doped MIS HFETs fabricated have thus been proved to exhibit the high current density, reduced gate leakage current, and relatively high transconductance, hence, promising for high-power applications.
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85.30.Tv Field effect devices
77.22.Ch Permittivity (dielectric function)

Suppression of DC bias stress-induced degradation of organic field-effect transistors using postannealing effects

Tsuyoshi Sekitani, Shingo Iba, Yusaku Kato, Yoshiaki Noguchi, Takao Someya, and Takayasu Sakurai

Appl. Phys. Lett. 87, 073505 (2005); http://dx.doi.org/10.1063/1.2031932 (3 pages) | Cited 41 times

Online Publication Date: 9 August 2005

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We fabricate pentacene field-effect transistors (FETs) showing a very small degradation in performance under a continuous DC bias stress. Pentacene FETs are manufactured on polyimide films with polyimide gate dielectric layers, and then encapsulated by poly-chloro-para-xylylene passivation layers, resulting in very flexible and heat-resistant devices. When such devices are annealed at 140 °C for 12 h in a nitrogen environment, the change in their source-drain current is 3±1% even after the application of continuous DC voltage biases of VDS = VGS = −40 V for 11 h. Furthermore, their mobility is increased by postannealing effects from 0.27 cm2/V sto 0.36 cm2/V s and their on/off ratio is also increased from 103 to 106.
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85.60.Jb Light-emitting devices
61.72.Cc Kinetics of defect formation and annealing

Physical and electrical properties of lanthanide-incorporated tantalum nitride for n-channel metal-oxide-semiconductor field-effect transistors

C. Ren, D. S. H. Chan, X. P. Wang, B. B. Faizhal, M.-F. Li, Y.-C. Yeo, A. D. Trigg, A. Agarwal, N. Balasubramanian, J. S. Pan, P. C. Lim, A. C. H. Huan, and D.-L. Kwong

Appl. Phys. Lett. 87, 073506 (2005); http://dx.doi.org/10.1063/1.1947901 (3 pages) | Cited 9 times

Online Publication Date: 10 August 2005

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Lanthanide-incorporated tantalum nitride (TaN) is studied as a potential metal gate candidate for n-channel metal-oxide-semiconductor field-effect transistors (n-MOSFETs). Lanthanides such as terbium (Tb), erbium (Er), and ytterbium (Yb) are introduced into TaN to form Ta1−xTbxNy, Ta1−xErxNy, and Ta1−xYbxNy metal gates, respectively, on SiO2 dielectric. The resistivity, crystallinity, film composition, and work function of Ta1−xTbxNy, Ta1−xErxNy, and Ta1−xYbxNy films were investigated at different post-metal-anneal temperatures and for different lanthanide concentrations. It was found that the work function of lanthanide-incorporated TaN can be effectively tuned by increasing the concentration of lanthanide. Work functions of about 4.2–4.3 eV can be achieved even after a 1000 °C rapid thermal anneal, making lanthanide-incorporated TaN a promising metal gate candidate for n-MOSFETs. The enhanced nitrogen concentration and the possible presence of lanthanide-N or Ta-N-lanthanide compounds in lanthanide-incorporated TaN film could be responsible for its chemical-thermal stability on SiO2.
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73.61.-r Electrical properties of specific thin films
68.55.-a Thin film structure and morphology
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.Cc Kinetics of defect formation and annealing
85.30.Tv Field effect devices

GaN resistive hydrogen gas sensors

Feng Yun, Serguei Chevtchenko, Yong-Tae Moon, Hadis Morkoç, Timothy J. Fawcett, and John T. Wolan

Appl. Phys. Lett. 87, 073507 (2005); http://dx.doi.org/10.1063/1.2031930 (3 pages) | Cited 12 times

Online Publication Date: 10 August 2005

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GaN epilayers grown by organometallic vapor phase epitaxy have been used to fabricate resistive gas sensors with a pair of planar ohmic contacts. Detectible sensitivity to H2 gas for a wide range of gas mixtures in an Ar ambient has been realized; the lowest concentration tested is ∼ 0.1% H2 (in Ar), well below the lower combustion limit in air. No saturation of the signal is observed up to 100% H2 flow. Real-time response to H2 shows a clear and sharp response with no memory effects during the ramping cycles of H2 concentration. The change in current at a fixed voltage to hydrogen was found to change with sensor geometry. This appears to be consistent with a surface-adsorption-induced change of conductivity; a detailed picture of the gas sensing mechanism requires further systematic studies.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Dual-gate organic thin-film transistors

G. H. Gelinck, E. van Veenendaal, and R. Coehoorn

Appl. Phys. Lett. 87, 073508 (2005); http://dx.doi.org/10.1063/1.2031933 (3 pages) | Cited 26 times

Online Publication Date: 10 August 2005

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A dual-gate organic thin-film transistor is realized using solution-processed organic semiconductor and insulator layers. Electrodes are made from gold. Compared to conventional single-gate transistors, this device type has a higher on current and steeper subthreshold slope. We show that the improved performance is the result of a nonconstant threshold voltage rather than formation of a second accumulation channel. Formation of a second accumulation channel does occur but the field-effect mobility associated with this channel is a factor 104 lower than the primary channel due to the relatively rough insulator-semiconductor interface.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Improvement of current-control induced by oxide notch in very short field-effect transistor

Nicolas Cavassilas, Marc Bescond, and Jean-Luc Autran

Appl. Phys. Lett. 87, 073509 (2005); http://dx.doi.org/10.1063/1.1994929 (3 pages) | Cited 2 times

Online Publication Date: 10 August 2005

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A two-dimensional quantum ballistic transport model based on the nonequilibrium Green’s function formalism has been used to theoretically investigate the effects induced by an oxide notch in a very short (7 nm) thin-film metal-oxide-semiconductor field-effect transistor. Our investigation shows that a well adjusted notch permits an improvement of on-off current ratio Ion/Ioff of about 244% with no detrimental change in the drive current Ion. This remarkable result is explained by a nontrivial influence of notch on conduction-band structure in thin film. Therefore, a well optimized notch seems to be a good solution to have a much better control of short channel effects in transistor where the transport has a strong quantum behavior.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Charge-trapping memory cell of SiO2/SiN/high‐k dielectric Al2O3 with TaN metal gate for suppressing backward-tunneling effect

Chang-Hyun Lee, Kyu-Charn Park, and Kinam Kim

Appl. Phys. Lett. 87, 073510 (2005); http://dx.doi.org/10.1063/1.2010607 (3 pages) | Cited 18 times

Online Publication Date: 11 August 2005

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We present a device structure of SiO2/SiN/Al2O3 (SANOS) with tantalum nitride (TaN) metal gate. When TaN metal gate is applied for the SANOS structure instead of commonly used n-type poly-silicon, the unwanted backward Fowler–Nordheim tunneling current of electron through the top oxide is significantly suppressed owing to its higher work function and better compatibility with high-k dielectrics. As a result, the program∕erase speed is significantly improved and the erase threshold voltage (VTH) can be obtained to be negative voltage of −3.5 V.
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85.50.Gk Non-volatile ferroelectric memories
84.30.Sk Pulse and digital circuits
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Solid-state current amplifier based on impact ionization

Hong-Wei Lee and Aaron R. Hawkins

Appl. Phys. Lett. 87, 073511 (2005); http://dx.doi.org/10.1063/1.2031929 (3 pages) | Cited 5 times

Online Publication Date: 11 August 2005

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The operation principle, fabrication, and measurement results for a stand-alone amplifier based on impact ionization are reported. The device was built in silicon using standard microelectronic processes. Testing was performed by connecting the device to both silicon and indium-gallium-arsenide photodiodes to demonstrate its compatibility with arbitrary current sources. Preamplified leakage currents of less than 1 nA were measured along with current gains greater than 100.
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85.30.De Semiconductor-device characterization, design, and modeling
84.30.Le Amplifiers
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