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7 Nov 2011

Volume 99, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 99, 193101 (2011); http://dx.doi.org/10.1063/1.3657777 (3 pages)

Sungwook Chung, Jonathan R. Felts, Debin Wang, William P. King, and James J. De Yoreo
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NpN-GaN/InxGa1−xN/GaN heterojunction bipolar transistor on free-standing GaN substrate

Zachary Lochner, Hee Jin Kim, Yi-Che Lee, Yun Zhang, Suk Choi, Shyh-Chiang Shen, P. Doug Yoder, Jae-Hyun Ryou, and Russell D. Dupuis

Appl. Phys. Lett. 99, 193501 (2011); http://dx.doi.org/10.1063/1.3659475 (3 pages) | Cited 1 time

Online Publication Date: 7 November 2011

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Data and analysis are presented for NpN-GaN/InGaN/GaN double-heterojunction bipolar transistors (HBTs) grown and fabricated on a free-standing GaN (FS-GaN) substrate in comparison to that on a sapphire substrate to investigate the effect of dislocations in III-nitride HBT epitaxial structures. The performance characteristics of HBTs on FS-GaN exhibit a maximum collector current density of ∼12.3 kA/cm2, dc current gain of ∼90, and maximum differential gain of ∼120 without surface passivation, representing a substantial improvement over similar devices grown on sapphire. This is attributed to the reduction in threading dislocation density afforded by using a homoepitaxial growth on a high-crystalline-quality substrate. The minority carrier diffusion length increases significantly owing to not only a mitigated carrier trap effect via fewer dislocations, but also possibly reduced microscopic localized states.
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85.30.Pq Bipolar transistors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Junctionless in-plane-gate transparent thin-film transistors

Jie Jiang, Jia Sun, Wei Dou, Bin Zhou, and Qing Wan

Appl. Phys. Lett. 99, 193502 (2011); http://dx.doi.org/10.1063/1.3659478 (3 pages)

Online Publication Date: 7 November 2011

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Junctionless transparent electric-double-layer thin-film transistors with an in-plane-gate figure are fabricated on glass substrates at room temperature. The unique feature of such junctionless transistors is that the channel and source/drain electrodes are the same thin indium-tin-oxide film without any source/drain junction. Effective field-effect modulation of drain current can be obtained when the indium-tin-oxide thickness is reduced to 20 nm. Such junctionless transparent thin-film transistors exhibit a good electrical performance with a small subthreshold swing (<0.2 V/decade), a high mobility (∼20 cm2/Vs), and a large on/off ratio (>106), respectively. A serial-capacitor model is proposed to understand the operation mechanism.
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85.30.Tv Field effect devices

Dirac voltage tunability by Hf1−xLaxO gate dielectric composition modulation for graphene field effect devices

Joong Gun Oh, Yunsang Shin, Woo Cheol Shin, Onejae Sul, and Byung Jin Cho

Appl. Phys. Lett. 99, 193503 (2011); http://dx.doi.org/10.1063/1.3659691 (3 pages)

Online Publication Date: 7 November 2011

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We report that the Dirac voltage of graphene field effect transistors (FETs) can be tuned by controlling the composition of hafnium lanthanum oxide (HfLaO) gate dielectrics. As the lanthanum percentage is increased in the HfLaO film, the charge neutrality point of the graphene FET is gradually shifted in the negative direction. The origin of this tuning is attributed to the hygroscopic nature of the lanthanum oxide, as it is found that lanthanum oxide in the HfLaO film absorbs water molecules below the graphene channel, resulting in the suppression of the p-doping in graphene.
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85.30.Tv Field effect devices

Presence and origin of interface charges at atomic-layer deposited Al2O3/III-nitride heterojunctions

Satyaki Ganguly, Jai Verma, Guowang Li, Tom Zimmermann, Huili Xing, and Debdeep Jena

Appl. Phys. Lett. 99, 193504 (2011); http://dx.doi.org/10.1063/1.3658450 (3 pages) | Cited 10 times

Online Publication Date: 9 November 2011

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Unlike silicon and traditional III-V semiconductors, the III-nitrides exhibit high spontaneous and piezoelectric polarization charges at epitaxial polar heterojunctions. In the process of investigating scaling properties of gate-stacks consisting atomic-layer deposited Al2O3/III-Nitride heterojunctions, we find interface charges that appear closely linked to the polarization charges of the underlying nitride substrate. Through capacitance-voltage measurement on a series of samples of varying dielectric thicknesses, we find the presence and propose an origin of benign donor-type interface charges (Qit ∼6 × 1013 cm−2) at the AlN/Al2O3 junction. This interface charge is almost equal to the net polarization charge in AlN. The polarization-related dielectric/AlN interface charge and the role of oxygen in the dielectric as a possible modulation dopant potentially offer opportunities for various device applications.
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85.30.Tv Field effect devices
85.40.Sz Deposition technology
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Reconstruction dependent reactivity of As-decapped In0.53Ga0.47As(001) surfaces and its influence on the electrical quality of the interface with Al2O3 grown by atomic layer deposition

A. Molle, L. Lamagna, C. Grazianetti, G. Brammertz, C. Merckling, M. Caymax, S. Spiga, and M. Fanciulli

Appl. Phys. Lett. 99, 193505 (2011); http://dx.doi.org/10.1063/1.3659688 (3 pages) | Cited 3 times

Online Publication Date: 9 November 2011

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Tuning the desorption temperature of an As cap layer allows to achieve In0.53Ga0.47As(001) surfaces with (2 × 4) and (4 × 2) reconstructions which exhibit different chemical reactivity upon exposure in atmospheric pressure. Trimethyl-Al based atomic layer deposition of Al2O3 films on the two exposed surfaces causes a non-equivalent interface composition. This behavior is associated with a worse electrical quality of the interface with the exposed (4 × 2) In0.53Ga0.47As reconstruction.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
82.45.Jn Surface structure, reactivity and catalysis
84.32.Tt Capacitors
85.30.Tv Field effect devices
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.40.Ns Metal-nonmetal contacts

Super-radiant Cherenkov backward-wave oscillator with cyclotron absorption

I. V. Bandurkin and A. V. Savilov

Appl. Phys. Lett. 99, 193506 (2011); http://dx.doi.org/10.1063/1.3659693 (3 pages) | Cited 1 time

Online Publication Date: 9 November 2011

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The use of the resonance cyclotron absorption in the Cherenkov electron oscillator, which operates in the non-stationary regime of the super-radiation of short powerful rf pulses, is proposed. Due to a non-linear character of the absorption, it suppresses spurious oscillations at a small-signal stage, but almost does not affect the non-linear process of the super-radiant generation. This provides a possibility for a significant increase of the peak power of the super-radiant rf pulse.
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84.30.Ng Oscillators, pulse generators, and function generators
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

A broadband acoustic omnidirectional absorber comprising positive-index materials

Rui-Qi Li, Xue-Feng Zhu, Bin Liang, Yong Li, Xin-Ye Zou, and Jian-Chun Cheng

Appl. Phys. Lett. 99, 193507 (2011); http://dx.doi.org/10.1063/1.3659690 (3 pages) | Cited 6 times

Online Publication Date: 10 November 2011

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We propose a broadband acoustic omnidirectional absorber (AOA) made of acoustic metamaterials having a positive index, which guides an incident acoustic wave into a central cavity spirally without backscattering. Numerical simulations show that the AOA has an absorption cross section remarkably larger than its cavity within a broad band, which is of potential practical significance to various applications such as sound absorption and noise control. A possible scheme for the practical realization of the AOA is also briefly discussed.
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43.20.-f General linear acoustics
43.50.-x Noise: its effects and control

III-V Nitride based piezoresistive microcantilever for sensing applications

Muhammad Qazi, Nicholas DeRoller, Abdul Talukdar, and Goutam Koley

Appl. Phys. Lett. 99, 193508 (2011); http://dx.doi.org/10.1063/1.3657467 (3 pages) | Cited 3 times

Online Publication Date: 11 November 2011

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III-V Nitride based microcantilevers, with AlGaN/GaN heterostructure field effect transistor as the piezoresistive deflection transducer, have been investigated under steady state, transient, ac, and UV illuminated conditions and compared to theoretical calculations. The steady state transverse gauge factor (GFt) was found to be much larger than theoretical estimates and increased regularly with more negative gate bias. Transient GFt demonstrated opposite sign but similar gate bias dependence and was measured as high as ∼860. Measurements under ac biasing conditions and UV illumination resulted in a lower GFt of ∼13, which agrees with theoretical calculations owing to elimination of charge trapping effects.
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07.10.Cm Micromechanical devices and systems
85.30.Tv Field effect devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
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