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15 Mar 2010

Volume 96, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 96, 111901 (2010); http://dx.doi.org/10.1063/1.3358107 (3 pages)

B. Rožič, S. Krause, H. Finkelmann, G. Cordoyiannis, and Z. Kutnjak
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Scanning gate microscopy of current-annealed single layer graphene

M. R. Connolly, K. L. Chiou, C. G. Smith, D. Anderson, G. A. C. Jones, A. Lombardo, A. Fasoli, and A. C. Ferrari

Appl. Phys. Lett. 96, 113501 (2010); http://dx.doi.org/10.1063/1.3327829 (3 pages) | Cited 16 times

Online Publication Date: 15 March 2010

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We have used scanning gate microscopy to explore the local conductivity of a current-annealed graphene flake. A map of the local neutrality point (NP) after annealing at low current density exhibits micron-sized inhomogeneities. Broadening of the local e-h transition is also correlated with the inhomogeneity of the NP. Annealing at higher current density reduces the NP inhomogeneity, but we still observe some asymmetry in the e-h conduction. We attribute this to a hole-doped domain close to one of the metal contacts combined with underlying striations in the local NP.
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73.61.Wp Fullerenes and related materials
72.80.Vp Electronic transport in graphene
61.72.Cc Kinetics of defect formation and annealing

High-gain integrated inverters based on ZnO metal-semiconductor field-effect transistor technology

H. Frenzel, F. Schein, A. Lajn, H. von Wenckstern, and M. Grundmann

Appl. Phys. Lett. 96, 113502 (2010); http://dx.doi.org/10.1063/1.3339876 (3 pages) | Cited 11 times

Online Publication Date: 15 March 2010

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We report on the design and fabrication of ZnO-based integrated inverters consisting of normally-on metal-semiconductor field-effect transistors and AgxO Schottky diodes as level shifters. The inverters show high gain values up to 197 at 3 V operating voltage and low uncertainty levels in the range of 0.13 V. The influence of the level shifter and the channel material/thickness on the performance of the inverters has been investigated. Using Zn0.997Mg0.003O for the channel thin film leads to high reproducibility (90%) of the devices. A logic NOR-gate has been implemented showing the possibility to fabricate a complete logic.
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85.30.Tv Field effect devices
85.30.Kk Junction diodes
84.30.Sk Pulse and digital circuits
81.05.Dz II-VI semiconductors

Periodic anchoring condition for alignment of a short pitch cholesteric liquid crystal in uniform lying helix texture

Gurumurthy Hegde and Lachezar Komitov

Appl. Phys. Lett. 96, 113503 (2010); http://dx.doi.org/10.1063/1.3357420 (3 pages) | Cited 8 times

Online Publication Date: 15 March 2010

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Due to flexoelectricity, a cholesteric liquid crystal unidirectionally aligned in a sandwich cell, with its helix lying parallel to the confining cell substrates, exhibit a flexoelectro-optic response when subjected to an electric field applied perpendicular to the helix axis. The clarity of the flexoelectro-optic response is dependent on the quality of the uniformly lying helix texture of the cholesteric which often is difficult to achieve. Herein, a method for alignment of a short pitch cholesteric in such a texture by means of a periodic surface anchoring condition with periodicity matching that of the cholesteric liquid crystal is described.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
78.15.+e Optical properties of fluid materials, supercritical fluids and liquid crystals
77.65.Bn Piezoelectric and electrostrictive constants
78.20.Jq Electro-optical effects
42.70.Df Liquid crystals

High-performance CF4 plasma treated polycrystalline silicon thin-film transistors using a high-k Tb2O3 gate dielectric

Tung-Ming Pan and Zhi-Hong Li

Appl. Phys. Lett. 96, 113504 (2010); http://dx.doi.org/10.1063/1.3357428 (3 pages) | Cited 3 times

Online Publication Date: 15 March 2010

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In this letter, we have developed a high-k Tb2O3 gate dielectric polycrystalline silicon (poly-Si) thin-film transistors (TFTs) prepared under a CF4 plasma treatment. A high-performance TFT device that has a low threshold voltage of 0.89 V, a high effective carrier mobility of 59.6 cm2/V s, a small subthreshold swing of 212 mV/dec, and a high ION/IOFF current ratio of 8.15×106 can be achieved. This phenomenon is attributed to fluorine atoms into poly-Si films can effectively passivate the trap states near the Tb2O3/poly-Si interface. The fluorine incorporation also enhanced electrical reliability of the Tb2O3 poly-Si TFT. All of these results suggest that the CF4 plasma-treated poly-Si Tb2O3 TFT is a good candidate for high-performance TFTs.
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85.30.Tv Field effect devices
77.55.df For silicon electronics
72.20.Fr Low-field transport and mobility; piezoresistance
73.20.-r Electron states at surfaces and interfaces
81.65.Rv Passivation

Polarizer-free and fast response microlens arrays using polymer-stabilized blue phase liquid crystals

Yi-Hsin Lin, Hung-Shan Chen, Hung-Chun Lin, Yu-Shih Tsou, Hsu-Kuan Hsu, and Wang-Yang Li

Appl. Phys. Lett. 96, 113505 (2010); http://dx.doi.org/10.1063/1.3360860 (3 pages) | Cited 25 times

Online Publication Date: 15 March 2010

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We demonstrate polarizer-free and fast response microlens arrays based on optical phase modulation of polymer-stabilized blue phase liquid crystal (PSBP-LC). Polarization-independent optical phase shift is because the propagation of an incident light is along the optic axis of PSBP-LC, and birefringence of PSBP-LC induced by Kerr effect results in electrically tunable optical phase shift. The measured optical phase shift of a PSBP-LC phase modulation is around π radian at 150 Vrms for the cell gap of 7 μ. The response time is about 3 ms. The focal length is around 13.1 cm at 100 Vrms.
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42.79.Bh Lenses, prisms and mirrors
42.70.Df Liquid crystals
42.79.Hp Optical processors, correlators, and modulators
42.25.Lc Birefringence
42.25.Dd Wave propagation in random media
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Modeling and characterization of metal-semiconductor-metal-based source-drain contacts in amorphous InGaZnO thin film transistors

Sangwon Lee, Jun-Hyun Park, Kichan Jeon, Sungchul Kim, Yongwoo Jeon, Dae Hwan Kim, Dong Myong Kim, Jae Chul Park, and Chang Jung Kim

Appl. Phys. Lett. 96, 113506 (2010); http://dx.doi.org/10.1063/1.3364134 (3 pages) | Cited 10 times

Online Publication Date: 15 March 2010

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Due to the inherent property of large contact and parasitic resistances in amorphous InGaZnO (a-IGZO) thin film transistors (TFTs), a metal-semiconductor-metal (MSM) structure is a key element in a-IGZO TFTs. Therefore, voltage drops across resistances and MSM structure should be fully considered in the modeling and characterization of a-IGZO TFTs. A physics-based semiempirical model for the current-voltage characteristics of the MSM structure for the source-channel-drain contact in a-IGZO TFTs is proposed and verified with experimental results. The proposed model for the current in a-IGZO MSM structures includes a thermionic field emission [JTFE∝exp(VR,Schottky/Vo)] and trap-assisted generation (Jgen∝math) in addition to the thermionic emission current (JS: Independent of the bias) under reverse bias. Experimental result suggests that electrical characteristics of the MSM structure depend not only on the Schottky barrier but also on the bulk property of the a-IGZO active layer.
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85.30.Tv Field effect devices
81.05.Gc Amorphous semiconductors
79.40.+z Thermionic emission
85.30.De Semiconductor-device characterization, design, and modeling

Hyper-interface, the bridge between radiative wave and evanescent wave

Zheng Liu, Zixian Liang, Xunya Jiang, Xinhua Hu, Xin Li, and Jian Zi

Appl. Phys. Lett. 96, 113507 (2010); http://dx.doi.org/10.1063/1.3280383 (3 pages) | Cited 5 times

Online Publication Date: 16 March 2010

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We investigate optical properties of the interface between the anisotropic metamaterial with hyperbolic dispersion and the isotropic dielectric. With material dispersion, a comprehensive theory is constructed, and the hyper-lens effect that the evanescent wave can be converted into the radiative wave is confirmed. At the inverse process of hyper-lens, we find a mechanism to compress and stop (slow) light at wide frequency range, which can be used as a removable memory or a light trap. All theoretical results are demonstrated by finite-difference time-domain simulation.
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42.70.-a Optical materials
02.70.Bf Finite-difference methods
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

Strain evolution during the silicidation of nanometer-scale SiGe semiconductor devices studied by dark field electron holography

David Cooper, Armand Béché, Jean-Michel Hartmann, Véronique Carron, and Jean-Luc Rouvière

Appl. Phys. Lett. 96, 113508 (2010); http://dx.doi.org/10.1063/1.3358149 (3 pages) | Cited 10 times

Online Publication Date: 16 March 2010

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SiGe is routinely used to induce strain in modern semiconductors in order to improve the mobility of the carriers in the channel. Due to the absence of a technique that can accurately measure the strain in these devices with nanometer-scale resolution it has been difficult to assess the effects of processing such as silicidation on the compressive strain in the conduction channel. Here we show that by using dark field electron holography, the strain evolution at various stages of the device processing can be observed, showing that the silicidation process does in fact significantly reduce the strain in the conduction channel.
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85.30.De Semiconductor-device characterization, design, and modeling
85.35.-p Nanoelectronic devices

Physics of base charge dynamics in the three port transistor laser

H. W. Then, M. Feng, and N. Holonyak

Appl. Phys. Lett. 96, 113509 (2010); http://dx.doi.org/10.1063/1.3364143 (3 pages) | Cited 2 times

Online Publication Date: 17 March 2010

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The base charge dynamics of the quantum-well (QW) transistor laser (TL) is analyzed by constructing a model based on earlier incomplete charge control analysis. We extend Kirchhoff’s Law to include electrical and consistently “optical” elements. The model yields, via microwave measurements (and resolvable picosecond responses), physical quantities associated with TL base-charging, permitting the extraction of a base QW charge density, nQW = 2×1016 cm−3, consistent with calculation by current continuity. The low density implies quasi-Fermi level discontinuity in the TL base, and indicates that the base QW charge level is not as important as the current driving the QW and supplying electron-hole recombination.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Thermal stability of TiN metal gate prepared by atomic layer deposition or physical vapor deposition on HfO2 high-K dielectric

L. Wu, H. Y. Yu, X. Li, K. L. Pey, J. S. Pan, J. W. Chai, Y. S. Chiu, C. T. Lin, J. H. Xu, H. J. Wann, X. F. Yu, D. Y. Lee, K. Y. Hsu, and H. J. Tao

Appl. Phys. Lett. 96, 113510 (2010); http://dx.doi.org/10.1063/1.3365241 (3 pages) | Cited 10 times

Online Publication Date: 18 March 2010

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In this paper, the thermal stability of TiN metal gate with various composition prepared by different preparation technology [(e.g., atomic layer deposition (ALD) or physical vapor deposition (PVD)] on HfO2 high-K dielectric is investigated and compared by physical and electrical analysis. After annealing of the TiN/HfO2 stack at 1000 °C for 30 s, it is observed that: (1) Nitrogen tends to out-diffuse from TiN for all the samples; (2) Oxygen from the interfacial layer (IL) between HfO2 and Si tends to diffuse toward TiN. PVD Ti-rich TiN shows a wider oxygen distribution in the gate stack, and a thinner IL than the N-rich sample. Ti penetration into HfO2 is also observed in the Ti-rich sample, which can potentially lead to the dielectric break-down. Besides, the oxygen out-diffusion can be significantly suppressed for ALD TiN compared to the PVD TiN samples.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.22.Jp Dielectric breakdown and space-charge effects
81.40.Gh Other heat and thermomechanical treatments
79.60.Dp Adsorbed layers and thin films
68.55.ag Semiconductors
77.55.D- High-permittivity gate dielectric films

Minimizing the scattering of a nonmagnetic cloak

Jingjing Zhang, Yu Luo, and Niels Asger Mortensen

Appl. Phys. Lett. 96, 113511 (2010); http://dx.doi.org/10.1063/1.3366726 (3 pages) | Cited 10 times

Online Publication Date: 19 March 2010

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Nonmagnetic cloak offers a feasible way to achieve invisibility at optical frequencies using materials with only electric responses. In this letter, we suggest an approximation of the ideal nonmagnetic cloak and quantitatively study its electromagnetic characteristics using a full-wave scattering theory. It is demonstrated that the forward scattering of the impedance matched cloak increases dramatically as the thickness of the cloak decreases. Nevertheless, it is still possible to effectively reduce the total scattering cross section with a very thin cloak whose impedance is not matched to the surrounding material at the outer boundary. Our analysis also provides the flexibility of reducing the scattering in an arbitrary direction.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
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