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17 Oct 2011

Volume 99, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 99, 163301 (2011); http://dx.doi.org/10.1063/1.3651509 (3 pages)

Jonathan E. Allen, Kevin G. Yager, Htay Hlaing, Chang-Yong Nam, Benjamin M. Ocko, and Charles T. Black
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Fractal phononic crystals in aluminum nitride: An approach to ultra high frequency bandgaps

Nai-Kuei Kuo and Gianluca Piazza

Appl. Phys. Lett. 99, 163501 (2011); http://dx.doi.org/10.1063/1.3651760 (3 pages) | Cited 5 times

Online Publication Date: 18 October 2011

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This letter reports on the design and experimental demonstration of a microscale fractal-like phononic bandgap (PBG) structure in aluminum nitride (AlN). The micro-fabricated fractal phononic crystals (PnCs) exhibit two frequency stop bands for symmetric lamb waves in the Γ-Χ direction centered about 900 MHz (bandwidth of 11.1%) and 1.10 GHz (bandwidth of 9.1%) with maximum acoustic rejection of 40 dB. Differently from the conventional phononic bandgap designs, the unit cell consists of a center air square scatterer with four side air square scatterers repeating at its corners. The presence of these side squares essentially shortens the scattering distance between the unit cells and translates into the suppression of higher frequency vibrational modes. In other words, this design is capable of extending the frequency of operation of the PBGs for a given unit cell and minimum feature size. For the purpose of the demonstration, AlN lamb wave transducers were utilized to launch symmetric lamb waves into the PBG structure. The evidence of direct in-plane integration between the transducers and the PnC structure operating in the ultra high frequency range lays the foundation for the development of ultrasonic devices based on PBGs.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Qs Photonic bandgap materials
05.45.Df Fractals

Calculation of the capacitance-voltage characteristic of GaAs, In0.53Ga0.47As, and InAs metal-oxide-semiconductor structures

T. P. O’Regan and P. K. Hurley

Appl. Phys. Lett. 99, 163502 (2011); http://dx.doi.org/10.1063/1.3652699 (3 pages) | Cited 4 times

Online Publication Date: 18 October 2011

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The capacitance-voltage characteristic of GaAs, In0.53Ga0.47As, and InAs metal-oxide-semiconductor capacitors (MOSCAPs) is calculated in three cases. First, quantization is not considered, then quantization of the Γ-valley is included, and finally quantization of the Γ-, X-, and L-valleys is included. The choice of valley energy-minima is shown to determine the onset of occupation of the satellite valleys and corresponding increase in total capacitance. An equivalent-oxide-thickness correction is defined and used as a figure-of-merit to compare III-V to Si MOSCAPs and as a metric for the density-of-states bottleneck.
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84.32.Tt Capacitors

Designing acoustic transformation devices using fluid homogenization of an elastic substructure

Christopher N. Layman, Theodore P. Martin, Kimberly M. Moore, David C. Calvo, and Gregory J. Orris

Appl. Phys. Lett. 99, 163503 (2011); http://dx.doi.org/10.1063/1.3652914 (3 pages) | Cited 3 times

Online Publication Date: 18 October 2011

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The design of devices using finite embedded coordinate transformations presents an unique approach to control acoustic waves. Though combining the use of conformal mappings may provide a pathway to more realizable material properties, many device geometries still require combinations of density and sound speed which are unavailable in isotropic materials. Here, we present a design strategy based on a multiple scattering homogenization method to approximate the unique values required within such a device. We apply the method, using full-wave simulations, to the design of an aqueous cylindrical-to-plane wave lens, which can be constructed from simple materials.
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43.38.-p Transduction; acoustical devices for the generation and reproduction of sound

Terahertz instability of field effect transistor in quantum regime

Li-Ping Zhang and Ju-Kui Xue

Appl. Phys. Lett. 99, 163504 (2011); http://dx.doi.org/10.1063/1.3655200 (3 pages)

Online Publication Date: 19 October 2011

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The current-carrying state of a field effect transistor (FET) with asymmetric source and drain boundary conditions may become unstable and lead to generation of terahertz radiation. While previous studies of this instability are limited to the classical case, we extend this analysis to the nanometer FET with quantum effects. We find that quantum effects broaden the instability range of the drift velocity and enhance the radiation frequencies and the output power. These properties could make the nanometer FET advantageous for realization of practical terahertz oscillations.
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85.30.Tv Field effect devices

Side-gate effects on the direct current and radio frequency characteristics of AlGaN/GaN high-electron-mobility transistor on Si

Hong Zhou, Geok Ing Ng, Zhi Hong Liu, and Subramaniam Arulkumaran

Appl. Phys. Lett. 99, 163505 (2011); http://dx.doi.org/10.1063/1.3655350 (3 pages)

Online Publication Date: 21 October 2011

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The influence of the side-gate bias on the direct current and radio frequency characteristics for a GaN high electron mobility transistor is studied. When the side-gate is biased at large negative bias (VSG = −100 V), the maximum drain current density (Idmax), maximum extrinsic transconductance (gmmax), cut-off frequency (fT), and maximum oscillation frequency (fmax) of the device are reduced and the threshold voltage (Vth) is positively shifted. The drain leakage current under pinch-off is decreased. In contrast, when VSG is positive, there are only small changes for the fT, fmax, Idmax, gmmax, and Vth. The drain leakage current under pinch-off condition is increased at VSG = +100 V. It is believed that the electrical field effect and buffer depletion caused by the additional side gate voltage contribute to those changes.
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85.30.Tv Field effect devices

Electron holography characterization of the electrostatic potential of thin high-κ dielectric film embedded in gate stack

Y. Yao (姚湲), Y. Yang (杨阳), X. F. Duan (段晓峰), Y. G. Wang (王岩国), R. C. Yu (禹日成), and Q. X. Xu (徐秋霞)

Appl. Phys. Lett. 99, 163506 (2011); http://dx.doi.org/10.1063/1.3652770 (3 pages)

Online Publication Date: 21 October 2011

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The electrostatic potential of the thin high-κ dielectric film and related interfaces embedded in the gate stack can be profiled in high spatial resolution in the wedge-shape sample. The retrieved potential uncovers the uneven distribution with a maximum 15.6 ± 0.7 V in HfLaON dielectric film. It implies the non-uniform material distribution in high-κ thin film and physical parameter of the film, such as permittivity, should not be considered as the constant.
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77.55.df For silicon electronics
77.22.Ch Permittivity (dielectric function)
73.61.Ng Insulators
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